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Home ‣ Java Programming ‣ Garbage Collections See What Others Are Saying!
  • Question

  • When is the Demo object eligible for garbage collection? 
    class Test 
{  
    private Demo d; 
    void start() 
    {  
        d = new Demo(); 
        this.takeDemo(d); /* Line 7 */
    } /* Line 8 */
    void takeDemo(Demo demo) 
    { 
        demo = null;  
        demo = new Demo(); 
    } 
}


  • Options
  • A. After line 7
  • B. After line 8
  • C. After the start() method completes
  • D. When the instance running this code is made eligible for garbage collection.

  • Correct Answer
  • When the instance running this code is made eligible for garbage collection. 

    Explanation
    Option D is correct. By a process of elimination.

    Option A is wrong. The variable d is a member of the Test class and is never directly set to null.

    Option B is wrong. A copy of the variable d is set to null and not the actual variable d.

    Option C is wrong. The variable d exists outside the start() method (it is a class member). So, when the start() method finishes the variable d still holds a reference.

    • More questions

    • 1. What will be the output of the program? 
      class Super
{ 
    public int i = 0; 

    public Super(String text) /* Line 4 */
    {
        i = 1; 
    } 
} 

class Sub extends Super
{
    public Sub(String text)
    {
        i = 2; 
    } 

    public static void main(String args[])
    {
        Sub sub = new Sub("Hello"); 
        System.out.println(sub.i); 
    } 
}

    • Options
    • A. 0
    • B. 1
    • C. 2
    • D. Compilation fails.
      • Discuss
    • 2. What will be the output of the program (in jdk1.6 or above)? 
      public class BoolTest 
{
    public static void main(String [] args) 
    {
        Boolean b1 = new Boolean("false");
        boolean b2;
        b2 = b1.booleanValue();
        if (!b2) 
        {
            b2 = true;
            System.out.print("x ");
        }
        if (b1 & b2) /* Line 13 */
        {
            System.out.print("y ");
        }
        System.out.println("z");
    }
}

    • Options
    • A. z
    • B. x z

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