Constructors Practice

Sample questions

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1. Sample 1difficulty 2/5

   public class Counter {
       private int count;
       public Counter() { count = 0; }
       public void inc() { count++; }
       public int getCount() { return count; }
   }
   // ...
   Counter c = new Counter();
   c.inc(); c.inc(); c.inc();
   System.out.println(c.getCount());

   What is printed?

   • A

     3

     check_circle
   • B

     0

   • C

     1

   • D

     Compile-time error

   Why

   The default constructor sets count to 0; inc() is called three times, so count becomes 3.

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2. Sample 2difficulty 2/5

   public class Foo {
       public void Foo() {
           System.out.println("ctor?");
       }
   }
   // ...
   Foo f = new Foo();

   What happens?

   • A

     Nothing is printed; Java's default constructor was used

     check_circle
   • B

     Run-time error

   • C

     Compile-time error

   • D

     ctor? is printed

   Why

   Foo here is a regular method (it has return type void), not a constructor; the implicit default constructor runs and produces no output.

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3. Sample 3difficulty 2/5

   public class Greeter {
       private String greeting;
       public Greeter() { greeting = "Hello"; }
       public Greeter(String g) { greeting = g; }
       public String say() { return greeting; }
   }
   // ...
   Greeter g = new Greeter("Hola");
   System.out.println(g.say());

   What is printed?

   • A

     Hola

     check_circle
   • B

     Hello

   • C

     null

   • D

     Compile-time error

   Why

   The String-parameter constructor sets greeting to "Hola".

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4. Sample 4difficulty 2/5

   public class Point {
       private int x, y;
       public Point(int x, int y) {
           this.x = x;
           this.y = y;
       }
       public int getX() { return x; }
       public int getY() { return y; }
   }
   // ...
   Point p = new Point(4, 7);
   System.out.println(p.getX() + "," + p.getY());

   What is printed?

   • A

     Compile-time error

   • B

     7,4

   • C

     0,0

   • D

     4,7

     check_circle

   Why

   The constructor uses this.x = x and this.y = y to assign instance variables, so getX returns 4 and getY returns 7.

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5. Sample 5difficulty 2/5

   public class Item {
       private String name;
       private double price;
       public Item() { name = "?"; price = 0.0; }
       public Item(String n, double p) { name = n; price = p; }
       public String getName() { return name; }
   }
   // ...
   Item i = new Item();
   System.out.println(i.getName());

   What is printed?

   • A

     0.0

   • B

     null

   • C

     ?

     check_circle
   • D

     Compile-time error

   Why

   The no-argument constructor sets name to "?" and price to 0.0.

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