Mutator Methods Practice

Sample questions

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1. Sample 1difficulty 2/5

   public class Box {
       private int size;
       public Box() { size = 1; }
       public void setSize(int s) { size = s; }
       public int getSize() { return size; }
   }
   // ...
   Box b = new Box();
   b.setSize(10);
   System.out.println(b.getSize());

   What is printed?

   • A

     1

   • B

     0

   • C

     Compile-time error

   • D

     10

     check_circle

   Why

   The mutator setSize assigns 10 to size, which getSize then returns.

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2. Sample 2difficulty 2/5

   public class Age {
       private int years;
       public void setYears(int y) {
           if (y >= 0) years = y;
       }
       public int getYears() { return years; }
   }
   // ...
   Age a = new Age();
   a.setYears(-3);
   a.setYears(20);
   System.out.println(a.getYears());

   What is printed?

   • A

     -3

   • B

     20

     check_circle
   • C

     0

   • D

     17

   Why

   The negative value is rejected by the validation guard; setting 20 succeeds.

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3. Sample 3difficulty 2/5

   public class Switch {
       private boolean on;
       public void toggle() { on = !on; }
       public boolean isOn() { return on; }
   }
   // ...
   Switch s = new Switch();
   s.toggle(); s.toggle(); s.toggle();
   System.out.println(s.isOn());

   What is printed?

   • A

     Compile-time error

   • B

     false

   • C

     1

   • D

     true

     check_circle

   Why

   Starting from false: toggle to true, toggle to false, toggle to true. Final value true.

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4. Sample 4difficulty 3/5

   public class Stat {
       private int total = 0;
       private int count = 0;
       public void add(int v) {
           total += v;
           count++;
       }
       public double avg() {
           if (count == 0) return 0;
           return (double) total / count;
       }
   }
   // ...
   Stat s = new Stat();
   s.add(2); s.add(4); s.add(6);
   System.out.println(s.avg());

   What is printed?

   • A

     0.0

   • B

     3.0

   • C

     4.0

     check_circle
   • D

     12.0

   Why

   total=12 and count=3; 12.0/3 yields 4.0.

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5. Sample 5difficulty 3/5

   A typical "setter" for <code>private int age;</code>

   • A

     private void setAge(int a) { age = a; }

   • B

     public void setAge(int a) { age = a; }

     check_circle
   • C

     public void setAge() { age = 0; }

   • D

     public int setAge(int a) { age = a; }

   Why

   Setters return void and take a parameter for the new value.

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