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
2. CPU
3. Memory CPU
4. Memory CPU I/O
5. Memory CPU I/O Battery
6. Battery Memory CPU I/O
7. Battery Battery Memory CPU I/O
8. Battery Battery Memory CPU I/O
9. Battery Battery Memory CPU I/O
10. Battery Battery Battery Memory CPU I/O
11. Battery Battery Battery Memory CPU I/O
12. Battery Battery Battery Memory CPU I/O
13. Memory CPU I/O
14. Memory CPU I/O
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
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
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
18. I/O Memory CPU What's next after macro?
19. I/O Memory CPU What's next after macro? • Move on to so-called micro
20. I/O Memory CPU What's next after macro? • Move on to so-called micro • Spectrum of optimizations, not binary
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
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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108. public String names(List<User> users) {
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109. public String names(List<User> users) {
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111. public String names(List<User> users) {
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116. public String names(List<User> users) {
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117. public String names(List<User> users) {
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 StringBuilder builder = new StringBuilder(avg * users.size());
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118. public String names(List<User> 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(", ");
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 }X
 return builder.toString();
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119. for (int x = 0; x < valueCount; x++) {
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 dirtyFiles[x] = new File(directory, key + "." + x + ".tmp");
 }X
120. for (int x = 0; x < valueCount; x++) {
 StringBuilder b1 = new StringBuilder();
 b1.append(key);
 b1.append(".");
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 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
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
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
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
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
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
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
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
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
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
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
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
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
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
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.
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.
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
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<String> names(List<User> users) {
 List<String> names = new ArrayList<>(users.size());
 for (User user : users) {
 names.add(user.name);
 }X
 return unmodifiableList(names);
 }X
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
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
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
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);
 }
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
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
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
145. public boolean firstShorterThan(List<String> strings, int max) {
 for (int i = 0; i < strings.size(); i++) {
 if (strings.get(i).length() > max) {
 return i;
 }X
 }X
 return -1;
 }X
146. public boolean firstShorterThan(List<String> 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
147. public boolean firstShorterThan(List<String> 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
148. public boolean firstShorterThan(List<String> strings, int max) {
 for (int i = 0;ciy<sstrings.size();xi++) {
 if (strings.get(i).length() > max) {
 return i;
 }X
 }X
 return -1;
 }X
149. public boolean firstShorterThan(List<String> 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
150. public boolean firstShorterThan(List<String> 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
151. public boolean firstShorterThan(List<String> 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
152. public boolean firstShorterThan(List<String> 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
154. invokestatic static methods
155. invokestatic static methods class Test {
 public static void main(String... args) {
 staticMethod();
 } 
 public static void staticMethod() {
 System.out.println("Hello, static method!");
 }
 }
156. invokestatic static methods public static void main(java.lang.String...); Code: 0: invokestatic #2 // Method staticMethod:()V 3: return
157. invokestatic static methods invokespecial constructors private methods super methods
158. invokestatic static methods invokespecial constructors private methods super methods Test(); Code: 0: aload_0 1: invokespecial #1 // Method java/lang/Object."<init>":()V 4: return
159. invokestatic static methods invokespecial constructors private methods super methods invokevirtual other class methods
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!");
 }
 }
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
162. invokestatic static methods invokespecial constructors private methods super methods invokevirtual other class methods invokeinterface interface methods
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<String> names = Arrays.asList("Alice", "Bob", "Eve");
 int size = names.size();
 System.out.println(size);
 }
 }
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
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
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
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
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
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
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
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
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
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
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 ...
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
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
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 ...
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 ...
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 ...
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();
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
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
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
184. public boolean firstShorterThan(List<String> 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()
185. public boolean firstShorterThan(List<String> 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()
186. public boolean firstShorterThan(List<String> 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
187. public boolean firstShorterThan(List<String> 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
188. What about JIT & AOT compilers?
189. Resources res = getResources();
190. Resources res = getResources(); public Resources getResources() {
 return mResources;
 }X private Resources mResources;
191. Resources res = mResources; private Resources mResources;
192. Resources res = mResources; private Resources mResources; mResources
193. Resources res = mResources; private Resources mResources; mResources Memory lookup
194. Resources res = mResources; private Resources mResources; mResources Memory lookup Copy to local
195. Resources res = mResources; private Resources mResources; mResources Memory lookup Copy to local mResources mResources mResources mResources
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
197. for (int i = 0; i < strings.size(); i++)
198. for (int i = 0; i < strings.size(); i++) @Override public int size() {
 return ;
 } int size; 
 size
199. for (int i = 0; ix< strings. ;yi++) int size; size
200. for (int i = 0; ix< strings.size;yi++) int size; size
201. for (int i = 0; ix< strings.size;yi++) int size; size Memory lookup Copy to local
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
203. for (int i = 0; ix< strings.size;yi++) int size;
204. for (int i = 0, size = strings.size; ix< size;yi++) int size;
205. for (int i = 0, size = strings.size; ix< size;yi++) int size; Memory lookup Copy to local size
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<String> names(List<User> users) {
 List<String> names = new ArrayList<>(users.size());
 for (User user : users) {
 names.add(user.name);
 }X
 return unmodifiableList(names);
 }X
207. public List<String> names(List<User> users) {
 List<String> names = new ArrayList<>(users.size());
 for (User user : users) {
 names.add(user.name);
 }X
 return unmodifiableList(names);
 }X
208. public List<String> names(List<User> users) {
 List<String> names = new ArrayList<>(users.size());
 for (Iterator<User> iter = users.iterator(); iter.hasNext(); ) {
 User user = iter.next();
 names.add(user.name);
 }X
 return unmodifiableList(names);
 }X
209. public List<String> names(List<User> users) {
 List<String> names = new ArrayList<>(users.size());
 for (Iterator<User> iter = users.iterator(); iter.hasNext(); ) {
 User user = iter.next();
 names.add(user.name);
 }X
 return unmodifiableList(names);
 }X
210. public List<String> names(List<User> users) {
 List<String> names = new ArrayList<>(users.size());
 for (Iterator<User> iter = users.iterator(); iter.hasNext(); ) {
 User user = iter.next();
 names.add(user.name);
 }X
 return unmodifiableList(names);
 }X
211. public List<String> names(List<User> users) {
 List<String> names = new ArrayList<>(users.size());
 for (Iterator<User> iter = users.iterator(); iter.hasNext(); ) {
 User user = iter.next();
 names.add(user.name);
 }X
 return unmodifiableList(names);
 }X
212. public List<String> names(List<User> users) {
 List<String> names = new ArrayList<>(users.size());
 for (Iterator<User> iter = users.iterator(); iter.hasNext(); ) {
 User user = iter.next();
 names.add(user.name);
 }X
 return unmodifiableList(names);
 }X
213. public List<String> names(List<User> users) {
 List<String> names = new ArrayList<>(users.size());
 for (Iterator<User> iter = users.iterator(); iter.hasNext(); ) {
 User user = iter.next();
 names.add(user.name);
 }X
 return unmodifiableList(names);
 }X
214. public List<String> names(List<User> users) {
 List<String> 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
215. public List<String> names(List<User> users) {
 List<String> 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
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
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
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
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
221. jakewharton jakewharton jakewharton twitter.com/ google.com/+ .com Eliminating Code Overhead