CSE110 Lecture 10

Principles of Programming with Java
switch Statement and Operator ?
(202005)

Transcript

1. CSE110
   Principles of Programming
   with Java
   Lecture 10:
   switch Statement and Operator ?
   Javier Gonzalez-Sanchez
   javiergs@asu.edu
   javiergs.engineering.asu.edu | javiergs.com
   Office Hours: By appointment
   

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2. switch Statement
   

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3. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 3
   The switch Statement
   • The switch statement provides another means to
   decide which statement to execute next
   • The switch statement evaluates an expression, then
   attempts to match the result to one of several
   possible cases
   • Each case contains a value and a list of statements
   • The flow of control transfers to statement associated
   with the first value that matches
   

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4. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 4
   The switch Statement
   • The general syntax of a switch statement is
   

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5. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 5
   Example 1A
   String s = JOptionPane.showInputDialog(“Write a number”):
   int option = Integer.parseInt(s);
   switch (option) {
   case 1: System.out.println(“Phoenix”); break;
   case 2: System.out.println(“NY”); break;
   case 3: System.out.println(“Seattle”); break;
   default: System.out.println(“Error”); break;
   }
   System.out.println(“Bye.”);
   

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6. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 6
   Example 1B
   String s = JOptionPane.showInputDialog(“Write a number”):
   int option = Integer.parseInt(s);
   switch (option) {
   case 1: System.out.println(“Phoenix”); break;
   case 2: System.out.println(“NY”); break;
   case 3: System.out.println(“Seattle”); break;
   }
   System.out.println(“Bye.”);
   

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7. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 7
   Example 1C
   String s = JOptionPane.showInputDialog(“Write a number”):
   int option = Integer.parseInt(s);
   switch (option) {
   case 1: System.out.println(“Phoenix”);
   case 2: System.out.println(“NY”);
   case 3: System.out.println(“Seattle”);
   default: System.out.println(“Error”);
   }
   System.out.println(“Bye.”);
   

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8. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 8
   Example 1D
   String s = JOptionPane.showInputDialog(“Write a number”):
   int option = Integer.parseInt(s);
   switch (option) {
   case 1: System.out.println(“Phoenix”); break;
   case 2: System.out.println(“NY”); break;
   case 3: System.out.println(“Seattle”); break;
   default: System.out.println(“Error”);
   }
   System.out.println(“Bye.”);
   

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9. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 9
   The switch Statement
   • The expression of a switch statement must result in
   an int or a char
   • It cannot be a boolean value, a floating-point value
   (float or double)
   • A switch statement tries to match the expression
   with a value
   • You cannot perform relational checks with a switch
   statement
   

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10. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 10
    break
    • Often a break statement is used as the last
    statement in each case's statement list
    • A break statement causes control to transfer to the
    end of the switch statement
    • If a break statement is not used, the flow of control
    will continue into the next case
    

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11. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 11
    default
    • A switch statement can have an optional default case
    • The default case has no associated value and simply
    uses the reserved word default
    • If the default case is present, control will transfer to it if no
    other case value matches
    • Though the default case can be positioned anywhere in
    the switch, usually it is placed at the end
    • If there is no default case, and no other value matches,
    control falls through to the statement after the switch
    

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12. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 12
    Example 2 | using char
    String s = JOptionPane.showInputDialog(“Write a letter”):
    char letter = s.charAt(0);
    switch (letter) {
    case 'A':
    System.out.println("It is an A");
    break;
    case 'B':
    System.out.println("It is a B");
    break;
    case 'C':
    System.out.println("It is a C");
    break;
    default:
    System.out.println("Invalid option");
    }
    

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13. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 13
    Example 3
    String s = JOptionPane.showInputDialog(“Write your grade”);
    int grade = Integer.parseInt(s);
    switch (grade) {
    case 100: System.out.println(“A+”); break;
    case 95:
    case 90: System.out.println(“A”); break;
    case 85:
    case 80: System.out.println(“B”); break;
    default: System.out.println(“C”);
    }
    System.out.println(“Bye.”);
    // What is the result for grade = 97 ?
    

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14. The operator ?
    

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15. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 15
    The Conditional Operator
    • Java has a conditional operator that evaluates a
    boolean condition that determines which of two
    other expressions is evaluated
    • The result of the chosen expression is the result of
    the entire conditional operator
    • Its syntax is:
    condition ? expression1 : expression2
    • If the condition is true, expression1 is evaluated; if it
    is false, expression2 is evaluated
    

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16. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 16
    The Conditional Operator
    • The conditional operator is similar to an if-else
    statement, except that it forms an expression that
    returns a value
    • For example:
    larger = ((num1 > num2) ? num1 : num2);
    • If num1 is greater that num2, then num1 is assigned
    to larger; otherwise,num2 is assigned to larger
    • The conditional operator is ternary because it
    requires three operands
    

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17. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 17
    Example
    System.out.println ("Your change is "
    + count
    + ((count == 1) ? "Dime" : "Dimes"));
    • If count equals 1, then "Dime" is printed
    • If count is anything other than 1, then "Dimes" is
    printed
    

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18. CSE110 - Principles of Programming
    Javier Gonzalez-Sanchez
    javiergs@asu.edu
    Summer 2020
    Disclaimer. These slides can only be used as study material for the class CSE110 at ASU. They cannot be distributed or used for another purpose.
    

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