Eliminating Code Overhead (Square HQ 2015)

The CPU, RAM, and disk are finite resources that are often taken for granted as unbounded. Not only is this obviously untrue, but the use of these resources directly affects the most important resource on a mobile device: the battery. This talk will focus on techniques that both libraries and applications can implement to ensure their effect is in general without overhead.

Video: https://youtu.be/b6zKBZcg5fk

Transcript

1. Eliminating Code Overhead
   Jake Wharton
   

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2. CPU
   

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3. Memory
   CPU
   

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4. Memory
   CPU
   I/O
   

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5. Memory
   CPU
   I/O
   Battery
   

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6. Battery
   Memory
   CPU
   I/O
   

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7. Battery
   Battery
   Memory
   CPU
   I/O
   

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8. Battery
   Battery
   Memory
   CPU
   I/O
   

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9. Battery
   Battery
   Memory
   CPU
   I/O
   

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10. Battery
    Battery
    Battery
    Memory
    CPU
    I/O
    

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11. Battery
    Battery
    Battery
    Memory
    CPU
    I/O
    

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12. Battery
    Battery
    Battery
    Memory
    CPU
    I/O
    

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13. Memory
    CPU
    I/O
    

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14. Memory
    CPU
    I/O
    

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15. • Do not nest multi-pass layouts
    • Lazily compute complex data when needed
    • Cache heavy computational results for re-use
    • Consider RenderScript for performance
    • Keep work off of the main thread
    Memory
    CPU
    I/O
    

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16. • Use object pools and caches to reduce churn
    • Be mindful of the overhead of enums
    • Do not allocate inside the draw path
    • Use specialized collections instead of JDK
    collections when appropriate (SparseArray)
    Memory
    CPU
    I/O
    

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17. Memory
    CPU
    I/O
    • Batch operations with reasonable back-off
    policies
    • Use gzip or binary serialization format
    • Cache data offline with TTLs for reloading
    • Use JobScheduler API to batch across OS
    

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18. I/O
    Memory
    CPU
    What's next after macro?
    

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19. I/O
    Memory
    CPU
    What's next after macro?
    • Move on to so-called micro
    

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20. I/O
    Memory
    CPU
    What's next after macro?
    • Move on to so-called micro
    • Spectrum of optimizations, not binary
    

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21. I/O
    Memory
    CPU
    What's next after macro?
    • Move on to so-called micro
    • Spectrum of optimizations, not binary
    • Do not blindly apply to everything, only when appropriate
    

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22. I/O
    Memory
    CPU
    What's next after macro?
    • Move on to so-called micro
    • Spectrum of optimizations, not binary
    • Do not blindly apply to everything, only when appropriate
    • Multiple micro-optimizations can improve like a macro
    

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23. public List names(List users) {

    List names = new ArrayList<>();

    for (User user : users) {

    names.add(user.name);

    }

    return unmodifiableList(names);

    }
    

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24. public List names(List users) {

    List names = new ArrayList<>();

    for (User user : users) {

    names.add(user.name);

    }

    return unmodifiableList(names);

    }
    

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25. public List names(List users) {

    List names = new ArrayList<>();

    for (User user : users) {

    names.add(user.name);

    }

    return unmodifiableList(names);

    }
    

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26. public List names(List users) {

    List names = new ArrayList<>();

    for (User user : users) {

    names.add(user.name);

    }

    return unmodifiableList(names);

    }
    

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27. public List names(List users) {

    List names = new ArrayList<>();

    for (User user : users) {

    names.add(user.name);

    }

    return unmodifiableList(names);

    }
    

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28. public List names(List users) {

    List names = new ArrayList<>();

    for (User user : users) {

    names.add(user.name);

    }

    return unmodifiableList(names);

    }
    

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29. public List names(List users) {

    List names = new ArrayList<>();

    for (User user : users) {

    names.add(user.name);

    }

    return unmodifiableList(names);

    }
    

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30. public List names(List users) {

    List names = new ArrayList<>();

    for (User user : users) {

    names.add(user.name);

    }

    return unmodifiableList(names);

    }
    

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31. public List names(List users) {

    List names = new ArrayList<>();

    for (User user : users) {

    names.add(user.name);

    }

    return unmodifiableList(names);

    }
    

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32. public List names(List users) {

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    return unmodifiableList(names);

    }
    

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33. public List names(List users) {

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    return unmodifiableList(names);

    }
    

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34. public List names(List users) {

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    }
    

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35. public List names(List users) {

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36. public List names(List users) {

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37. public List names(List users) {

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38. public List names(List users) {

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    }
    

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39. public List names(List users) {

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    }X
    

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40. public List names(List users) {

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41. public List names(List users) {

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42. public List names(List users) {

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43. public List names(List users) {

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44. public List names(List users) {

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45. public List names(List users) {

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46. public List names(List users) {

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47. public List names(List users) {

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48. public List names(List users) {

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49. public List names(List users) {

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50. public List names(List users) {

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51. public List names(List users) {

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52. public List names(List users) {

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53. public List names(List users) {

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54. public List names(List users) {

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55. public List names(List users) {

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56. public List names(List users) {

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58. public List names(List users) {

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59. public List names(List users) {

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63. public List names(List users) {

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64. public List names(List users) {

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69. public List names(List users) {

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73. public List names(List users) {

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80. public String names(List users) {

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82. public String names(List users) {

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90. Jimmy•McNulty
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    Jimmy•McNulty,•
    

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91. public String names(List users) {

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92. public String names(List users) {

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    Stringer•Bell
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93. public String names(List users) {

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94. public String names(List users) {

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    Jimmy•McNulty,•
    Stringer•Bell
    Jimmy•McNulty,•
    

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95. public String names(List users) {

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    Jimmy•McNulty,•
    

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96. public String names(List users) {

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    Stringer•Bell
    Jimmy•McNulty,•
    

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97. public String names(List users) {

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    Stringer•Bell
    Jimmy•McNulty,•
    

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98. public String names(List users) {

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    Jimmy•McNulty,•Stringer•Bell
    

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99. public String names(List users) {

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    Jimmy•McNulty,•Stringer•Bell
    

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100. public String names(List users) {

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     Jimmy•McNulty,•Stringer•Bell
     

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101. public String names(List users) {

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     builder.append(user.name);

     }X

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     Jimmy•McNulty,•Stringer•Bell
     Jimmy•McNulty,•Stringer•Bell,•
     

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102. public String names(List users) {

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     if (builder.length() > 0) builder.append(", ");

     builder.append(user.name);

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     return builder.toString();

     }X
     Jimmy•McNulty,•Stringer•Bell,•
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103. public String names(List users) {

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     return builder.toString();

     }X
     Jimmy•McNulty,•Stringer•Bell,•
     Bunk•Moreland
     Jimmy•McNulty,•Stringer•Bell,•
     

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104. public String names(List users) {

     StringBuilder builder = new StringBuilder();

     for (User user : users) {

     if (builder.length() > 0) builder.append(", ");

     builder.append(user.name);

     }X

     return builder.toString();

     }X
     Jimmy•McNulty,•Stringer•Bell,•
     Bunk•Moreland
     Jimmy•McNulty,•Stringer•Bell,•
     

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105. public String names(List users) {

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     Jimmy•McNulty,•Stringer•Bell,•
     Bunk•Moreland
     Jimmy•McNulty,•Stringer•Bell,•
     

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106. public String names(List users) {

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     if (builder.length() > 0) builder.append(", ");

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     Jimmy•McNulty,•Stringer•Bell,•
     

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107. public String names(List users) {

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     if (builder.length() > 0) builder.append(", ");

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     Jimmy•McNulty,•Stringer•Bell,•
     

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108. public String names(List users) {

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     if (builder.length() > 0) builder.append(", ");

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     Bunk•Moreland
     Jimmy•McNulty,•Stringer•Bell,•
     

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109. public String names(List users) {

     StringBuilder builder = new StringBuilder();

     for (User user : users) {

     if (builder.length() > 0) builder.append(", ");

     builder.append(user.name);

     }X

     return builder.toString();

     }X
     Jimmy•McNulty,•Stringer•Bell,•Bunk•Moreland
     

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110. public String names(List users) {

     StringBuilder builder = new StringBuilder();

     for (User user : users) {

     if (builder.length() > 0) builder.append(", ");

     builder.append(user.name);

     }X

     return builder.toString();

     }X
     Jimmy•McNulty,•Stringer•Bell,•Bunk•Moreland
     

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111. public String names(List users) {

     StringBuilder builder = new StringBuilder();

     for (User user : users) {

     if (builder.length() > 0) builder.append(", ");

     builder.append(user.name);

     }X

     return builder.toString();

     }X
     Jimmy•McNulty,•Stringer•Bell,•Bunk•Moreland
     

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112. public String names(List users) {

     StringBuilder builder = new StringBuilder();

     for (User user : users) {

     if (builder.length() > 0) builder.append(", ");

     builder.append(user.name);

     }X

     return builder.toString();

     }X
     Jimmy•McNulty,•Stringer•Bell,•Bunk•Moreland
     Jimmy•McNulty,•Stringer•Bell,•Bunk•Moreland,•
     

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113. public String names(List users) {

     StringBuilder builder = new StringBuilder();

     for (User user : users) {

     if (builder.length() > 0) builder.append(", ");

     builder.append(user.name);

     }X

     return builder.toString();

     }X
     Jimmy•McNulty,•Stringer•Bell,•Bunk•Moreland,•
     

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114. public String names(List users) {

     StringBuilder builder = new StringBuilder();

     for (User user : users) {

     if (builder.length() > 0) builder.append(", ");

     builder.append(user.name);

     }X

     return builder.toString();

     }X
     Jimmy•McNulty,•Stringer•Bell,•Bunk•Moreland,•
     Jimmy•McNulty,•Stringer•Bell,•Bunk•Moreland,•D'Angelo•Barksdale
     

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115. Jimmy•McNulty,•Stringer•Bell,•Bunk•Moreland,•D'Angelo•Barksdale
     public String names(List users) {

     StringBuilder builder = new StringBuilder();

     for (User user : users) {

     if (builder.length() > 0) builder.append(", ");

     builder.append(user.name);

     }X

     return builder.toString();

     }X
     

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116. public String names(List users) {

     StringBuilder builder = new StringBuilder();

     for (User user : users) {

     if (builder.length() > 0) builder.append(", ");

     builder.append(user.name);

     }X

     return builder.toString();

     }X
     

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117. public String names(List users) {

     int avg = 17; // Determined by exact science.

     StringBuilder builder = new StringBuilder(avg * users.size());

     for (User user : users) {

     if (builder.length() > 0) builder.append(", ");

     builder.append(user.name);

     }X

     return builder.toString();

     }X
     

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118. public String names(List users) {

     int avg = 17; // Determined by exact science.

     StringBuilder builder = new StringBuilder(avg * users.size());

     for (User user : users) {

     if (builder.length() > 0) builder.append(", ");

     builder.append(user.name);

     }X

     return builder.toString();

     }X
     

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119. for (int x = 0; x < valueCount; x++) {

     cleanFiles[x] = new File(directory, key + "." + x);

     dirtyFiles[x] = new File(directory, key + "." + x + ".tmp");

     }X
     

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120. for (int x = 0; x < valueCount; x++) {

     StringBuilder b1 = new StringBuilder();

     b1.append(key);

     b1.append(".");

     b1.append(x);

     cleanFiles[x] = new File(directory, b1.toString());

     StringBuilder b2 = new StringBuilder();

     b2.append(key);

     b2.append(".");

     b2.append(x);

     b2.append(".tmp");

     dirtyFiles[x] = new File(directory, b2.toString());

     }X
     

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121. for (int x = 0; x < valueCount; x++) {

     StringBuilder b1 = new StringBuilder();

     b1.append(key);

     b1.append(".");

     b1.append(x);

     cleanFiles[x] = new File(directory, b1.toString());

     StringBuilder b2 = new StringBuilder();

     b2.append(key);

     b2.append(".");

     b2.append(x);

     b2.append(".tmp");

     dirtyFiles[x] = new File(directory, b2.toString());

     }X
     

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122. for (int x = 0; x < valueCount; x++) {

     StringBuilder b = new StringBuilder();

     b.append(key);

     b.append(".");

     b.append(x);

     cleanFiles[x] = new File(directory, b.toString());

     b.append(".tmp");

     dirtyFiles[x] = new File(directory, b.toString());

     }X
     

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123. for (int x = 0; x < valueCount; x++) {

     StringBuilder b = new StringBuilder();

     b.append(key);

     b.append(".");

     b.append(x);

     cleanFiles[x] = new File(directory, b.toString());

     b.append(".tmp");

     dirtyFiles[x] = new File(directory, b.toString());

     }X
     

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124. StringBuilder b = new StringBuilder();

     b.append(key);

     b.append(".");
     for (int x = 0; x < valueCount; x++) {

     b.append(x);

     cleanFiles[x] = new File(directory, b.toString());

     b.append(".tmp");

     dirtyFiles[x] = new File(directory, b.toString());

     }X
     

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125. StringBuilder b = new StringBuilder();

     b.append(key);

     b.append(".");
     for (int x = 0; x < valueCount; x++) {

     b.append(x);

     cleanFiles[x] = new File(directory, b.toString());

     b.append(".tmp");

     dirtyFiles[x] = new File(directory, b.toString());

     }X
     

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126. StringBuilder b = new StringBuilder();

     b.append(key);

     b.append(".");
     int truncateTo = b.length();
     for (int x = 0; x < valueCount; x++) {

     b.append(x);

     cleanFiles[x] = new File(directory, b.toString());

     b.append(".tmp");

     dirtyFiles[x] = new File(directory, b.toString());

     }X
     

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127. StringBuilder b = new StringBuilder();

     b.append(key);

     b.append(".");
     int truncateTo = b.length();
     for (int x = 0; x < valueCount; x++) {

     b.append(x);

     cleanFiles[x] = new File(directory, b.toString());

     b.append(".tmp");

     dirtyFiles[x] = new File(directory, b.toString());

     }X
     

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128. StringBuilder b = new StringBuilder();

     b.append(key);

     b.append(".");
     int truncateTo = b.length();
     for (int x = 0; x < valueCount; x++) {

     b.append(x);

     cleanFiles[x] = new File(directory, b.toString());

     b.append(".tmp");

     dirtyFiles[x] = new File(directory, b.toString());
     b.setLength(truncateTo);

     }X
     

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129. StringBuilder b = new StringBuilder();

     b.append(key);

     b.append(".");
     int truncateTo = b.length();
     for (int x = 0; x < valueCount; x++) {

     b.append(x);

     cleanFiles[x] = new File(directory, b.toString());

     b.append(".tmp");

     dirtyFiles[x] = new File(directory, b.toString());
     b.setLength(truncateTo);

     }X
     

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130. StringBuilder b = new StringBuilder(key.length() + 6);

     b.append(key);

     b.append(".");
     int truncateTo = b.length();
     for (int x = 0; x < valueCount; x++) {

     b.append(x);

     cleanFiles[x] = new File(directory, b.toString());

     b.append(".tmp");

     dirtyFiles[x] = new File(directory, b.toString());
     b.setLength(truncateTo);

     }X
     

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131. StringBuilder b = new StringBuilder(key.length() + 6);

     b.append(key);

     b.append(".");
     int truncateTo = b.length();
     for (int x = 0; x < valueCount; x++) {

     b.append(x);

     cleanFiles[x] = new File(directory, b.toString());

     b.append(".tmp");

     dirtyFiles[x] = new File(directory, b.toString());
     b.setLength(truncateTo);

     }X
     

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132. StringBuilder b = new StringBuilder(key);

     b.append(".");
     int truncateTo = b.length();
     for (int x = 0; x < valueCount; x++) {

     b.append(x);

     cleanFiles[x] = new File(directory, b.toString());

     b.append(".tmp");

     dirtyFiles[x] = new File(directory, b.toString());
     b.setLength(truncateTo);

     }X
     

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133. StringBuilder b = new StringBuilder(key);

     b.append(".");
     int truncateTo = b.length();
     for (int x = 0; x < valueCount; x++) {

     b.append(x);

     cleanFiles[x] = new File(directory, b.toString());

     b.append(".tmp");

     dirtyFiles[x] = new File(directory, b.toString());
     b.setLength(truncateTo);

     }X
     

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134. StringBuilder b = new StringBuilder(key);

     b.append(".");
     int truncateTo = b.length();
     for (int x = 0; x < valueCount; x++) {

     b.append(x);

     cleanFiles[x] = new File(directory, b.toString());

     b.append(".tmp");

     dirtyFiles[x] = new File(directory, b.toString());
     public StringBuilder(String str)
     Constructs a string builder initialized to the contents of the specified string.
     The initial capacity of the string builder is 16 plus the length of the string
     argument.
     

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135. StringBuilder b = new StringBuilder(key);

     b.append(".");
     int truncateTo = b.length();
     for (int x = 0; x < valueCount; x++) {

     b.append(x);

     cleanFiles[x] = new File(directory, b.toString());

     b.append(".tmp");

     dirtyFiles[x] = new File(directory, b.toString());
     public StringBuilder(String str)
     Constructs a string builder initialized to the contents of the specified string.
     The initial capacity of the string builder is 16 plus the length of the string
     argument.
     

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136. StringBuilder b = new StringBuilder(key);

     b.append(".");
     int truncateTo = b.length();
     for (int x = 0; x < valueCount; x++) {

     b.append(x);

     cleanFiles[x] = new File(directory, b.toString());

     b.append(".tmp");

     dirtyFiles[x] = new File(directory, b.toString());
     b.setLength(truncateTo);

     }X
     

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137. StringBuilder b = new StringBuilder(key).append(".");
     int truncateTo = b.length();
     for (int x = 0; x < valueCount; x++) {

     b.append(x);

     cleanFiles[x] = new File(directory, b.toString());
     b.append(".tmp");

     dirtyFiles[x] = new File(directory, b.toString());
     b.setLength(truncateTo);

     }X
     public List names(List users) {

     List names = new ArrayList<>(users.size());

     for (User user : users) {

     names.add(user.name);

     }X

     return unmodifiableList(names);

     }X
     

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138. private int headerOffset;

     private int headerTop;

     private int animationHeight;

     

     @Override protected void onCreate(Bundle bundle) {

     super.onCreate(bundle);

     

     setTitle(getResources().getString(R.id.title));

     getWindow().setStatusBarColor(getResources().getColor(R.color.blue));

     

     headerOffset = getResources()
     .getDimensionPixelSize(R.dimen.header_offset);

     headerTop = getResources()
     .getDimensionPixelSize(R.dimen.header_top);

     animationHeight = getResources()
     .getDimensionPixelSize(R.dimen.animation_height);

     }X
     

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139. private int headerOffset;

     private int headerTop;

     private int animationHeight;

     

     @Override protected void onCreate(Bundle bundle) {

     super.onCreate(bundle);

     Resources res = getResources();

     

     setTitle(getResources().getString(R.id.title));

     getWindow().setStatusBarColor(getResources().getColor(R.color.blue));

     

     headerOffset = getResources()
     .getDimensionPixelSize(R.dimen.header_offset);

     headerTop = getResources()
     .getDimensionPixelSize(R.dimen.header_top);

     animationHeight = getResources()
     .getDimensionPixelSize(R.dimen.animation_height);

     }X
     

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140. private int headerOffset;

     private int headerTop;

     private int animationHeight;

     

     @Override protected void onCreate(Bundle bundle) {

     super.onCreate(bundle);

     Resources res = getResources();

     

     setTitle(res.getString(R.id.title));

     getWindow().setStatusBarColor(res.getColor(R.color.blue));

     

     headerOffset = res.getDimensionPixelSize(R.dimen.header_offset);

     headerTop = res.getDimensionPixelSize(R.dimen.header_top);

     animationHeight = res.getDimensionPixelSize(R.dimen.animation_height);

     }X
     

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141. private int headerOffset;

     private int headerTop;

     private int animationHeight;

     

     @Override protected void onCreate(Bundle bundle) {

     super.onCreate(bundle);

     Resources res = getResources();

     

     setTitle(res.getString(R.id.title));

     getWindow().setStatusBarColor(res.getColor(R.color.blue));

     

     headerOffset = res.getDimensionPixelSize(R.dimen.header_offset);

     headerTop = res.getDimensionPixelSize(R.dimen.header_top);

     animationHeight = res.getDimensionPixelSize(R.dimen.animation_height);

     }
     

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142. public boolean validIndices(int[] indices, String string) {

     for (int index : indices) {

     if (index < 0 && index >= string.length()) {

     return false;

     }X

     }X

     return true;

     }X
     

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143. public boolean validIndices(int[] indices, String string) {

     int len = string.length();

     for (int index : indices) {

     if (index < 0 && index >= len) {

     return false;

     }X

     }X

     return true;

     }X
     

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144. public boolean validIndices(int[] indices, String string) {

     int len = string.length();

     for (int index : indices) {

     if (index < 0 && index >= len) {

     return false;

     }X

     }X

     return true;

     }X
     

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145. public boolean firstShorterThan(List strings, int max) {

     for (int i = 0; i < strings.size(); i++) {

     if (strings.get(i).length() > max) {

     return i;

     }X

     }X

     return -1;

     }X
     

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146. public boolean firstShorterThan(List strings, int max) {

     int i = 0;

     while (i < strings.size()) {X

     if (strings.get(i).length() > max) {Y

     return i;

     }X

     i++;

     }X

     return -1;

     }X
     

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147. public boolean firstShorterThan(List strings, int max) {

     int i = 0;

     while (true) {X

     if (!(i < strings.size())) {

     break;

     }Y

     if (strings.get(i).length() > max) {Y

     return i;

     }X

     i++;

     }X

     return -1;

     }X
     

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148. public boolean firstShorterThan(List strings, int max) {

     for (int i = 0;ciyif (strings.get(i).length() > max) {

     return i;

     }X

     }X

     return -1;

     }X
     

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149. public boolean firstShorterThan(List strings, int max) {

     int size =sstrings.size();
     for (int i = 0;ciy< size;xi++) {

     if (strings.get(i).length() > max) {

     return i;

     }X

     }X

     return -1;

     }X
     

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150. public boolean firstShorterThan(List strings, int max) {

     int size =sstrings.size();
     for (int i = 0;ciy< size;xi++) {

     if (strings.get(i).length() > max) {

     return i;

     }X

     }X

     return -1;

     }X
     

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151. public boolean firstShorterThan(List strings, int max) {

     for (int i = 0, size = strings.size();ciy< size;xi++) {

     if (strings.get(i).length() > max) {

     return i;

     }X

     }X

     return -1;

     }X
     

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152. public boolean firstShorterThan(List strings, int max) {

     for (int i = 0, size = strings.size();ciy< size;xi++) {

     if (strings.get(i).length() > max) {

     return i;

     }X

     }X

     return -1;

     }X
     

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153. View Slide

154. invokestatic
     static methods
     

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155. invokestatic
     static methods
     class Test {

     public static void main(String... args) {

     staticMethod();

     }
     

     public static void staticMethod() {

     System.out.println("Hello, static method!");

     }

     }
     

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156. invokestatic
     static methods
     public static void main(java.lang.String...);
     Code:
     0: invokestatic #2 // Method staticMethod:()V
     3: return
     

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157. invokestatic
     static methods
     invokespecial
     constructors
     private methods
     super methods
     

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158. invokestatic
     static methods
     invokespecial
     constructors
     private methods
     super methods
     Test();
     Code:
     0: aload_0
     1: invokespecial #1 // Method java/lang/Object."":()V
     4: return
     

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159. invokestatic
     static methods
     invokespecial
     constructors
     private methods
     super methods
     invokevirtual
     other class
     methods
     

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160. invokestatic
     static methods
     invokespecial
     constructors
     private methods
     super methods
     invokevirtual
     other class
     methods
     class Test {

     public static void main(String... args) {

     new Test().method();

     }

     

     public void method() {

     System.out.println("Hello, method!");

     }

     }
     

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161. invokestatic
     static methods
     invokespecial
     constructors
     private methods
     super methods
     invokevirtual
     other class
     methods
     public static void main(java.lang.String...);
     Code:
     ...
     8: aload_1
     9: invokevirtual #4 // Method method:()V
     

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162. invokestatic
     static methods
     invokespecial
     constructors
     private methods
     super methods
     invokevirtual
     other class
     methods
     invokeinterface
     interface
     methods
     

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163. invokestatic
     static methods
     invokespecial
     constructors
     private methods
     super methods
     invokevirtual
     other class
     methods
     invokeinterface
     interface
     methods
     class Test {

     public static void main(String... args) {

     List names = Arrays.asList("Alice", "Bob", "Eve");

     int size = names.size();

     System.out.println(size);

     }

     }
     

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164. invokestatic
     static methods
     invokespecial
     constructors
     private methods
     super methods
     invokevirtual
     other class
     methods
     invokeinterface
     interface
     methods
     public static void main(java.lang.String...);
     Code:
     ...
     23: aload_1
     24: invokeinterface #7, 1 // InterfaceMethod java/util/List.size:()I
     

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165. public class MyActivity extends Activity {
     @Override protected void onCreate(Bundle bundle) {

     super.onCreate(bundle);

     Resources res = getResources();
     // ...

     }X
     @Override public String toString() {

     return "MyActivity";

     }X
     }X
     

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166. public class MyActivity extends Activity {
     @Override protected void onCreate(Bundle bundle) {

     super.onCreate(bundle);

     Resources res = getResources();
     // ...

     }X
     @Override public String toString() {

     return "MyActivity";

     }X
     }X
     Method Address
     

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167. public class MyActivity extends Activity {
     @Override protected void onCreate(Bundle bundle) {

     super.onCreate(bundle);

     Resources res = getResources();
     // ...

     }X
     @Override public String toString() {

     return "MyActivity";

     }X
     }X
     Method Address
     MyActivity
     Activity
     ContextThemeWrapper
     Context
     Object
     

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168. public class MyActivity extends Activity {
     @Override protected void onCreate(Bundle bundle) {

     super.onCreate(bundle);

     Resources res = getResources();
     // ...

     }X
     @Override public String toString() {

     return "MyActivity";

     }X
     }X
     Method Address
     MyActivity
     Activity
     ContextThemeWrapper
     Context
     Object
     

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169. public class MyActivity extends Activity {
     @Override protected void onCreate(Bundle bundle) {

     super.onCreate(bundle);

     Resources res = getResources();
     // ...

     }X
     @Override public String toString() {

     return "MyActivity";

     }X
     }X
     Method Address
     Object.toString 101
     MyActivity
     Activity
     ContextThemeWrapper
     Context
     Object
     

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170. public class MyActivity extends Activity {
     @Override protected void onCreate(Bundle bundle) {

     super.onCreate(bundle);

     Resources res = getResources();
     // ...

     }X
     @Override public String toString() {

     return "MyActivity";

     }X
     }X
     Method Address
     Object.toString 101
     Object.hashCode 102
     MyActivity
     Activity
     ContextThemeWrapper
     Context
     Object
     

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171. public class MyActivity extends Activity {
     @Override protected void onCreate(Bundle bundle) {

     super.onCreate(bundle);

     Resources res = getResources();
     // ...

     }X
     @Override public String toString() {

     return "MyActivity";

     }X
     }X
     Method Address
     Object.toString 101
     Object.hashCode 102
     ...
     MyActivity
     Activity
     ContextThemeWrapper
     Context
     Object
     

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172. Method Address
     Object.toString 101
     Object.hashCode 102
     ...
     public class MyActivity extends Activity {
     @Override protected void onCreate(Bundle bundle) {

     super.onCreate(bundle);

     Resources res = getResources();
     // ...

     }X
     @Override public String toString() {

     return "MyActivity";

     }X
     }X
     MyActivity
     Activity
     ContextThemeWrapper
     Context
     Object
     

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173. Method Address
     Object.toString 101
     Object.hashCode 102
     Context.getResources 201
     ...
     public class MyActivity extends Activity {
     @Override protected void onCreate(Bundle bundle) {

     super.onCreate(bundle);

     Resources res = getResources();
     // ...

     }X
     @Override public String toString() {

     return "MyActivity";

     }X
     }X
     MyActivity
     Activity
     ContextThemeWrapper
     Context
     Object
     

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174. public class MyActivity extends Activity {
     @Override protected void onCreate(Bundle bundle) {

     super.onCreate(bundle);

     Resources res = getResources();
     // ...

     }X
     @Override public String toString() {

     return "MyActivity";

     }X
     }X
     MyActivity
     Activity
     ContextThemeWrapper
     Context
     Object
     Method Address
     Object.toString 101
     Object.hashCode 102
     Context.getResources 201
     ...
     

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175. Method Address
     Object.toString 101
     Object.hashCode 102
     ContextTW.getResources 301
     ...
     public class MyActivity extends Activity {
     @Override protected void onCreate(Bundle bundle) {

     super.onCreate(bundle);

     Resources res = getResources();
     // ...

     }X
     @Override public String toString() {

     return "MyActivity";

     }X
     }X
     MyActivity
     Activity
     ContextThemeWrapper
     Context
     Object
     

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176. public class MyActivity extends Activity {
     @Override protected void onCreate(Bundle bundle) {

     super.onCreate(bundle);

     Resources res = getResources();
     // ...

     }X
     @Override public String toString() {

     return "MyActivity";

     }X
     }X
     Method Address
     Object.toString 101
     Object.hashCode 102
     ContextTW.getResources 301
     ...
     MyActivity
     Activity
     ContextThemeWrapper
     Context
     Object
     

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177. public class MyActivity extends Activity {
     @Override protected void onCreate(Bundle bundle) {

     super.onCreate(bundle);

     Resources res = getResources();
     // ...

     }X
     @Override public String toString() {

     return "MyActivity";

     }X
     }X
     MyActivity
     Activity
     ContextThemeWrapper
     Context
     Object
     Method Address
     Object.toString 101
     Object.hashCode 102
     ContextTW.getResources 301
     ...
     

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178. public class MyActivity extends Activity {
     @Override protected void onCreate(Bundle bundle) {

     super.onCreate(bundle);

     Resources res = getResources();
     // ...

     }X
     @Override public String toString() {

     return "MyActivity";

     }X
     }X
     MyActivity
     Activity
     ContextThemeWrapper
     Context
     Object
     Method Address
     MyActivity.toString 501
     Object.hashCode 102
     ContextTW.getResources 301
     ...
     

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179. public class MyActivity extends Activity {
     @Override protected void onCreate(Bundle bundle) {

     super.onCreate(bundle);

     Resources res = getResources();
     // ...

     }X
     @Override public String toString() {

     return "MyActivity";

     }X
     }X
     Method Address
     MyActivity.toString 501
     Object.hashCode 102
     ContextTW.getResources 301
     ...
     

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180. public class MyActivity extends Activity {
     @Override protected void onCreate(Bundle bundle) {

     super.onCreate(bundle);

     Resources res = getResources();
     // ...

     }X
     @Override public String toString() {

     return "MyActivity";

     }X
     }X
     Method Address
     MyActivity.toString 501
     Object.hashCode 102
     ContextTW.getResources 301
     ...
     getResources();
     

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181. public class MyActivity extends Activity {
     @Override protected void onCreate(Bundle bundle) {

     super.onCreate(bundle);

     Resources res = getResources();
     // ...

     }X
     @Override public String toString() {

     return "MyActivity";

     }X
     }X
     Method Address
     MyActivity.toString 501
     Object.hashCode 102
     ContextTW.getResources 301
     ...
     getResources(); Method table lookup
     

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182. public class MyActivity extends Activity {
     @Override protected void onCreate(Bundle bundle) {

     super.onCreate(bundle);

     Resources res = getResources();
     // ...

     }X
     @Override public String toString() {

     return "MyActivity";

     }X
     }X
     Method Address
     MyActivity.toString 501
     Object.hashCode 102
     ContextTW.getResources 301
     ...
     getResources(); Method table lookup Jump
     

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183. public class MyActivity extends Activity {
     @Override protected void onCreate(Bundle bundle) {

     super.onCreate(bundle);

     Resources res = getResources();
     // ...

     }X
     @Override public String toString() {

     return "MyActivity";

     }X
     }X
     Method Address
     MyActivity.toString 501
     Object.hashCode 102
     ContextTW.getResources 301
     ...
     getResources();
     getResources();
     getResources();
     getResources();
     getResources();
     Method table lookup Jump
     Method table lookup Jump
     Method table lookup Jump
     Method table lookup Jump
     Method table lookup Jump
     

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184. public boolean firstShorterThan(List strings, int max) {

     for (int i = 0; i < strings.size(); i++) {

     if (strings.get(i).length() > max) {

     return i;

     }X

     }X

     return -1;

     }X
     

     strings.size()
     

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185. public boolean firstShorterThan(List strings, int max) {

     for (int i = 0; i < strings.size(); i++) {

     if (strings.get(i).length() > max) {

     return i;

     }X

     }X

     return -1;

     }X
     strings.size()
     

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186. public boolean firstShorterThan(List strings, int max) {

     for (int i = 0; i < strings.size(); i++) {

     if (strings.get(i).length() > max) {

     return i;

     }X

     }X

     return -1;

     }X
     strings.size() Class lookup
     

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187. public boolean firstShorterThan(List strings, int max) {

     for (int i = 0; i < strings.size(); i++) {

     if (strings.get(i).length() > max) {

     return i;

     }X

     }X

     return -1;

     }X
     strings.size() Method table lookup Jump
     Class lookup
     

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188. What about JIT & AOT compilers?
     

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189. Resources res = getResources();
     

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190. Resources res = getResources();
     public Resources getResources() {

     return mResources;

     }X
     private Resources mResources;
     

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191. Resources res = mResources;
     private Resources mResources;
     

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192. Resources res = mResources;
     private Resources mResources;
     mResources
     

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193. Resources res = mResources;
     private Resources mResources;
     mResources Memory lookup
     

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194. Resources res = mResources;
     private Resources mResources;
     mResources Memory lookup Copy to local
     

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195. Resources res = mResources;
     private Resources mResources;
     mResources Memory lookup Copy to local
     mResources
     mResources
     mResources
     mResources
     

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196. Resources res = mResources;
     private Resources mResources;
     mResources Memory lookup Copy to local
     mResources
     mResources
     mResources
     mResources
     Memory lookup Copy to local
     Memory lookup Copy to local
     Memory lookup Copy to local
     Memory lookup Copy to local
     

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197. for (int i = 0; i < strings.size(); i++)
     

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198. for (int i = 0; i < strings.size(); i++)
     @Override
     public int size() {

     return ;

     }
     int size;
     

     size
     

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199. for (int i = 0; ix< strings. ;yi++)
     int size;
     size
     

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200. for (int i = 0; ix< strings.size;yi++)
     int size;
     size
     

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201. for (int i = 0; ix< strings.size;yi++)
     int size;
     size Memory lookup Copy to local
     

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202. for (int i = 0; ix< strings.size;yi++)
     int size;
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy to local
     size Memory lookup Copy
     size Memory lookup
     ookup Copy to local
     size Memory
     

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203. for (int i = 0; ix< strings.size;yi++)
     int size;
     

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204. for (int i = 0, size = strings.size; ix< size;yi++)
     int size;
     

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205. for (int i = 0, size = strings.size; ix< size;yi++)
     int size;
     Memory lookup Copy to local
     size
     

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206. StringBuilder b = new StringBuilder(key).append(".");
     int truncateTo = b.length();
     for (int x = 0; x < valueCount; x++) {

     b.append(x);

     cleanFiles[x] = new File(directory, b.toString());
     b.append(".tmp");

     dirtyFiles[x] = new File(directory, b.toString());
     b.setLength(truncateTo);

     }X
     public List names(List users) {

     List names = new ArrayList<>(users.size());

     for (User user : users) {

     names.add(user.name);

     }X

     return unmodifiableList(names);

     }X
     

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207. public List names(List users) {

     List names = new ArrayList<>(users.size());

     for (User user : users) {

     names.add(user.name);

     }X

     return unmodifiableList(names);

     }X
     

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208. public List names(List users) {

     List names = new ArrayList<>(users.size());

     for (Iterator iter = users.iterator(); iter.hasNext(); ) {

     User user = iter.next();

     names.add(user.name);

     }X

     return unmodifiableList(names);

     }X
     

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209. public List names(List users) {

     List names = new ArrayList<>(users.size());

     for (Iterator iter = users.iterator(); iter.hasNext(); ) {

     User user = iter.next();

     names.add(user.name);

     }X

     return unmodifiableList(names);

     }X
     

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210. public List names(List users) {

     List names = new ArrayList<>(users.size());

     for (Iterator iter = users.iterator(); iter.hasNext(); ) {

     User user = iter.next();

     names.add(user.name);

     }X

     return unmodifiableList(names);

     }X
     

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211. public List names(List users) {

     List names = new ArrayList<>(users.size());

     for (Iterator iter = users.iterator(); iter.hasNext(); ) {

     User user = iter.next();

     names.add(user.name);

     }X

     return unmodifiableList(names);

     }X
     

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212. public List names(List users) {

     List names = new ArrayList<>(users.size());

     for (Iterator iter = users.iterator(); iter.hasNext(); ) {

     User user = iter.next();

     names.add(user.name);

     }X

     return unmodifiableList(names);

     }X
     

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213. public List names(List users) {

     List names = new ArrayList<>(users.size());

     for (Iterator iter = users.iterator(); iter.hasNext(); ) {

     User user = iter.next();

     names.add(user.name);

     }X

     return unmodifiableList(names);

     }X
     

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214. public List names(List users) {

     List names = new ArrayList<>(users.size());

     for (int x = 0, size = users.size(); x < size; x++) {

     User user = users.get(x);

     names.add(user.name);

     }X

     return unmodifiableList(names);

     }X
     

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215. public List names(List users) {

     List names = new ArrayList<>(users.size());

     for (int x = 0, size = users.size(); x < size; x++) {

     User user = users.get(x);

     names.add(user.name);

     }X

     return unmodifiableList(names);

     }X
     

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216. StringBuilder b = new StringBuilder(key).append(".");
     int truncateTo = b.length();
     for (int x = 0; x < valueCount; x++) {

     b.append(x);

     cleanFiles[x] = new File(directory, b.toString());
     b.append(".tmp");

     dirtyFiles[x] = new File(directory, b.toString());
     b.setLength(truncateTo);

     }X
     

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217. int valueCount = this.valueCount;
     File directory = this.directory;
     File[] cleanFiles = this.cleanFiles;
     File[] dirtyFiles = this.dirtyFiles;
     StringBuilder b = new StringBuilder(key).append(".");
     int truncateTo = b.length();
     for (int x = 0; x < valueCount; x++) {

     b.append(x);

     cleanFiles[x] = new File(directory, b.toString());
     b.append(".tmp");

     dirtyFiles[x] = new File(directory, b.toString());
     b.setLength(truncateTo);

     }X
     

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218. StringBuilder b = new StringBuilder(key).append(".");
     int truncateTo = b.length();
     for (int x = 0; x < valueCount; x++) {

     b.append(x);

     cleanFiles[x] = new File(directory, b.toString());
     b.append(".tmp");

     dirtyFiles[x] = new File(directory, b.toString());
     b.setLength(truncateTo);

     }X
     

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219. What else?
     • Polymorphic virtual method calls
     • Monomorphic vs. bimorphic vs. megamorphic
     • Concurrency implications & locks
     • Read/write when lock, act out of lock
     • synchronized vs. concurrent lock types
     

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220. View Slide

221. jakewharton
     jakewharton
     jakewharton
     twitter.com/
     google.com/+
     .com
     Eliminating Code Overhead
     

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