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Home Java Programming Garbage Collections See What Others Are Saying!
  • Question
  • At what point is the Bar object, created on line 6, eligible for garbage collection?
    class Bar { } 
    class Test 
    {  
        Bar doBar() 
        {
            Bar b = new Bar(); /* Line 6 */
            return b; /* Line 7 */
        } 
        public static void main (String args[]) 
        { 
            Test t = new Test();  /* Line 11 */
            Bar newBar = t.doBar();  /* Line 12 */
            System.out.println("newBar"); 
            newBar = new Bar(); /* Line 14 */
            System.out.println("finishing"); /* Line 15 */
        } 
    }
    


  • Options
  • A. after line 12
  • B. after line 14
  • C. after line 7, when doBar() completes
  • D. after line 15, when main() completes

  • Correct Answer
  • after line 14 

    Explanation
    Option B is correct. All references to the Bar object created on line 6 are destroyed when a new reference to a new Bar object is assigned to the variable newBar on line 14. Therefore the Bar object, created on line 6, is eligible for garbage collection after line 14.

    Option A is wrong. This actually protects the object from garbage collection.

    Option C is wrong. Because the reference in the doBar() method is returned on line 7 and is stored in newBar on line 12. This preserver the object created on line 6.

    Option D is wrong. Not applicable because the object is eligible for garbage collection after line 14.


  • More questions

    • 1. Which three statements are true?
      1. f1 == f2
      2. f1 == f3
      3. f2 == f1[1]
      4. x == f1[0]
      5. f == f1[0]
      import java.awt.Button;
      class CompareReference 
      {
          public static void main(String [] args) 
          {
              float f = 42.0f;
              float [] f1 = new float[2];
              float [] f2 = new float[2];
              float [] f3 = f1;
              long x = 42;
              f1[0] = 42.0f;
          }
      }
      

    • Options
    • A. 1, 2 and 3
    • B. 2, 4 and 5
    • C. 3, 4 and 5
    • D. 1, 4 and 5
    • Discuss
    • 2. Which one create an anonymous inner class from within class Bar?
      class Boo 
      {
          Boo(String s) { }
          Boo() { }
      }
      class Bar extends Boo 
      {
          Bar() { }
          Bar(String s) {super(s);}
          void zoo() 
          {
          // insert code here
          }
      }
      

    • Options
    • A. Boo f = new Boo(24) { };
    • B. Boo f = new Bar() { };
    • C. Bar f = new Boo(String s) { };
    • D. Boo f = new Boo.Bar(String s) { };
    • Discuss
    • 3. Which of the following code fragments inserted, will allow to compile?
      public class Outer 
      { 
          public void someOuterMethod() 
          {
              //Line 5 
          } 
          public class Inner { } 
          
          public static void main(String[] argv) 
          {
              Outer ot = new Outer(); 
              //Line 10
          } 
      } 
      

    • Options
    • A. new Inner(); //At line 5
    • B. new Inner(); //At line 10
    • C. new ot.Inner(); //At line 10
    • D. new Outer.Inner(); //At line 10
    • Discuss
    • 4. What will be the output of the program?
      public class Test178 
      { 
          public static void main(String[] args) 
          {
              String s = "foo"; 
              Object o = (Object)s; 
              if (s.equals(o)) 
              { 
                  System.out.print("AAA"); 
              } 
              else 
              {
                  System.out.print("BBB"); 
              } 
              if (o.equals(s)) 
              {
                  System.out.print("CCC"); 
              } 
              else 
              {
                  System.out.print("DDD"); 
              } 
          } 
      }
      

    • Options
    • A. AAACCC
    • B. AAADDD
    • C. BBBCCC
    • D. BBBDDD
    • Discuss
    • 5. What will be the output of the program?
      int i = (int) Math.random();
      

    • Options
    • A. i = 0
    • B. i = 1
    • C. value of i is undetermined
    • D. Statement causes a compile error
    • Discuss
    • 6. What will be the output of the program?
      class Tree { } 
      class Pine extends Tree { } 
      class Oak extends Tree { } 
      public class Forest1 
      { 
          public static void main (String [] args)
          { 
              Tree tree = new Pine(); 
              if( tree instanceof Pine ) 
                  System.out.println ("Pine"); 
              else if( tree instanceof Tree ) 
                  System.out.println ("Tree"); 
              else if( tree instanceof Oak ) 
                  System.out.println ( "Oak" ); 
              else 
                  System.out.println ("Oops "); 
          } 
      }
      

    • Options
    • A. Pine
    • B. Tree
    • C. Forest
    • D. Oops
    • Discuss
    • 7. What will be the output of the program?
      public class StringRef 
      {
          public static void main(String [] args) 
          {
              String s1 = "abc";
              String s2 = "def";
              String s3 = s2;   /* Line 7 */
              s2 = "ghi";
              System.out.println(s1 + s2 + s3);
          }
      }
      

    • Options
    • A. abcdefghi
    • B. abcdefdef
    • C. abcghidef
    • D. abcghighi
    • Discuss
    • 8. What will be the output of the program?
      public class ObjComp 
      {
          public static void main(String [] args ) 
          {
              int result = 0;
              ObjComp oc = new ObjComp();
              Object o = oc;
      
              if (o == oc)  
                  result = 1;
              if (o != oc)  
                  result = result + 10;
              if (o.equals(oc) )  
                  result = result + 100;
              if (oc.equals(o) )  
                  result = result + 1000;
      
              System.out.println("result = " + result);
          }
      }
      

    • Options
    • A. 1
    • B. 10
    • C. 101
    • D. 1101
    • Discuss
    • 9. What will be the output of the program?
      String d = "bookkeeper";
      d.substring(1,7);
      d = "w" + d;
      d.append("woo");  /* Line 4 */
      System.out.println(d);
      

    • Options
    • A. wookkeewoo
    • B. wbookkeeper
    • C. wbookkeewoo
    • D. Compilation fails.
    • Discuss
    • 10. What will be the output of the program?
      interface Count 
      {
          short counter = 0;
          void countUp();
      }
      public class TestCount implements Count 
      {
          public static void main(String [] args) 
          {
              TestCount t = new TestCount();
              t.countUp();
          }
          public void countUp() 
          {
              for (int x = 6; x>counter; x--, ++counter) /* Line 14 */
              {
                  System.out.print(" " + counter);
              }
          }
      }
      

    • Options
    • A. 0 1 2
    • B. 1 2 3
    • C. 0 1 2 3
    • D. 1 2 3 4
    • E. Compilation fails
    • Discuss


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