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Home Java Programming Objects and Collections See What Others Are Saying!
  • Question
  • Which collection class allows you to grow or shrink its size and provides indexed access to its elements, but whose methods are not synchronized?


  • Options
  • A. java.util.HashSet
  • B. java.util.LinkedHashSet
  • C. java.util.List
  • D. java.util.ArrayList

  • Correct Answer
  • java.util.ArrayList 

    Explanation
    All of the collection classes allow you to grow or shrink the size of your collection. ArrayList provides an index to its elements. The newer collection classes tend not to have synchronized methods. Vector is an older implementation of ArrayList functionality and has synchronized methods; it is slower than ArrayList.

    More questions

    • 1. Which of the following is/are legal method declarations?

      1. protected abstract void m1();
      2. static final void m1(){}
      3. synchronized public final void m1() {}
      4. private native void m1();

    • Options
    • A. 1 and 3
    • B. 2 and 4
    • C. 1 only
    • D. All of them are legal declarations.
    • Discuss
    • 2. 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
    • 3. 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
    • 4. 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
    • 5. 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
    • 6. 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
    • 7. 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
    • 8. 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
    • 9. 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
    • 10. 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


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