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  • Question
  • What will be the output of the program?
    class A 
    { 
        public A(int x){} 
    } 
    class B extends A { } 
    public class test 
    { 
        public static void main (String args []) 
        {
            A a = new B(); 
            System.out.println("complete"); 
        } 
    }
    


  • Options
  • A. It compiles and runs printing nothing
  • B. Compiles but fails at runtime
  • C. Compile Error
  • D. Prints "complete"

  • Correct Answer
  • Compile Error 

    Explanation
    No constructor has been defined for class B therefore it will make a call to the default constructor but since class B extends class A it will also call the Super() default constructor.

    Since a constructor has been defined in class A java will no longer supply a default constructor for class A therefore when class B calls class A's default constructor it will result in a compile error.


    More questions

    • 1. Which one is a valid declaration of a boolean?

    • Options
    • A. boolean b1 = 0;
    • B. boolean b2 = 'false';
    • C. boolean b3 = false;
    • D. boolean b4 = Boolean.false();
    • E. boolean b5 = no;
    • Discuss
    • 2. What will be the output of the program?
      String a = "ABCD"; 
      String b = a.toLowerCase(); 
      b.replace('a','d'); 
      b.replace('b','c'); 
      System.out.println(b);
      

    • Options
    • A. abcd
    • B. ABCD
    • C. dccd
    • D. dcba
    • Discuss
    • 3. What will be the output of the program?
      class Q207 
      { 
          public static void main(String[] args) 
          {
              int i1 = 5; 
              int i2 = 6; 
              String s1 = "7"; 
              System.out.println(i1 + i2 + s1); /* Line 8 */
          } 
      }
      

    • Options
    • A. 18
    • B. 117
    • C. 567
    • D. Compiler error
    • Discuss
    • 4. In the given program, how many lines of output will be produced?
      public class Test 
      {
          public static void main(String [] args) 
          {
          int [] [] [] x = new int [3] [] [];
          int i, j;
          x[0] = new int[4][];
          x[1] = new int[2][];
          x[2] = new int[5][];
          for (i = 0; i < x.length; i++)
          {
              for (j = 0; j < x[i].length; j++) 
              {
                  x[i][j] = new int [i + j + 1];
                  System.out.println("size = " + x[i][j].length);
              }
          }
          }
      }
      

    • Options
    • A. 7
    • B. 9
    • C. 11
    • D. 13
    • E. Compilation fails
    • Discuss
    • 5. Which of the following statements about the hashcode() method are incorrect?

      1. The value returned by hashcode() is used in some collection classes to help locate objects.
      2. The hashcode() method is required to return a positive int value.
      3. The hashcode() method in the String class is the one inherited from Object.
      4. Two new empty String objects will produce identical hashcodes.

    • Options
    • A. 1 and 2
    • B. 2 and 3
    • C. 3 and 4
    • D. 1 and 4
    • Discuss
    • 6. What will be the output of the program?
      public class X 
      {
          public static void main(String [] args) 
          {
              String names [] = new String[5];
              for (int x=0; x < args.length; x++)
                  names[x] = args[x];
              System.out.println(names[2]);
          }
      }
      
      and the command line invocation is

      > java X a b


    • Options
    • A. names
    • B. null
    • C. Compilation fails
    • D. An exception is thrown at runtime
    • Discuss
    • 7. What will be the output of the program?
      class MyThread extends Thread 
      {
          public static void main(String [] args) 
          {
              MyThread t = new MyThread();
              t.start();
              System.out.print("one. ");
              t.start();
              System.out.print("two. ");
          }
          public void run() 
          {
              System.out.print("Thread ");
          }
      }
      

    • Options
    • A. Compilation fails
    • B. An exception occurs at runtime.
    • C. It prints "Thread one. Thread two."
    • D. The output cannot be determined.
    • Discuss
    • 8. What will be the output of the program?
      public class ExamQuestion7 
      {  
          static int j; 
          static void methodA(int i)
          {
              boolean b; 
              do
              { 
                  b = i<10 | methodB(4); /* Line 9 */
                  b = i<10 || methodB(8);  /* Line 10 */
              }while (!b); 
          } 
          static boolean methodB(int i)
          {
              j += i; 
              return true; 
          } 
          public static void main(String[] args)
          {
              methodA(0); 
              System.out.println( "j = " + j ); 
          } 
      }
      

    • Options
    • A. j = 0
    • B. j = 4
    • C. j = 8
    • D. The code will run with no output
    • Discuss
    • 9. The following block of code creates a Thread using a Runnable target:
      Runnable target = new MyRunnable();
      Thread myThread = new Thread(target);
      
      Which of the following classes can be used to create the target, so that the preceding code compiles correctly?

    • Options
    • A. public class MyRunnable extends Runnable{public void run(){}}
    • B. public class MyRunnable extends Object{public void run(){}}
    • C. public class MyRunnable implements Runnable{public void run(){}}
    • D. public class MyRunnable implements Runnable{void run(){}}
    • Discuss
    • 10. What will be the output of the program?
      public class WaitTest 
      {
          public static void main(String [] args) 
          {
              System.out.print("1 ");
              synchronized(args)
              {
                  System.out.print("2 ");
                  try 
                  {
                          args.wait(); /* Line 11 */
                  }
                  catch(InterruptedException e){ }
              }
              System.out.print("3 ");
          }
      }
      

    • Options
    • A. It fails to compile because the IllegalMonitorStateException of wait() is not dealt with in line 11.
    • B. 1 2 3
    • C. 1 3
    • D. 1 2
    • Discuss


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