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Home Java Programming Declarations and Access Control See What Others Are Saying!
  • Question
  • Which two code fragments will compile?
    1. interface Base2 implements Base {}
    2. abstract class Class2 extends Base
      { public boolean m1(){ return true; }}
    3. abstract class Class2 implements Base {}
    4. abstract class Class2 implements Base
      { public boolean m1(){ return (7 > 4); }}
    5. abstract class Class2 implements Base
      { protected boolean m1(){ return (5 > 7) }}
    interface Base 
    {
        boolean m1 ();
        byte m2(short s);
    }
    


  • Options
  • A. 1 and 2
  • B. 2 and 3
  • C. 3 and 4
  • D. 1 and 5

  • Correct Answer
  • 3 and 4 

    Explanation
    (3) is correct because an abstract class doesn't have to implement any or all of its interface's methods. (4) is correct because the method is correctly implemented ((7 > 4) is a boolean).

    (1) is incorrect because interfaces don't implement anything. (2) is incorrect because classes don't extend interfaces. (5) is incorrect because interface methods are implicitly public, so the methods being implemented must be public.


  • More questions

    • 1. What will be the output of the program?
      public class X 
      { 
          public static void main(String [] args) 
          {
              try 
              {
                  badMethod();  
                  System.out.print("A"); 
              }  
              catch (Exception ex) 
              {
                  System.out.print("B"); 
              }  
              finally 
              {
                  System.out.print("C"); 
              }  
              System.out.print("D"); 
          }  
          public static void badMethod() {} 
      } 
      

    • Options
    • A. AC
    • B. BC
    • C. ACD
    • D. ABCD
    • Discuss
    • 2. Which of the following line of code is suitable to start a thread?
      class X implements Runnable 
      { 
          public static void main(String args[]) 
          {
              /* Missing code? */
          } 
          public void run() {} 
      }
      

    • Options
    • A. Thread t = new Thread(X);
    • B. Thread t = new Thread(X); t.start();
    • C. X run = new X(); Thread t = new Thread(run); t.start();
    • D. Thread t = new Thread(); x.run();
    • Discuss
    • 3. What will be the output of the program?
      try 
      {
          Float f1 = new Float("3.0");
          int x = f1.intValue();
          byte b = f1.byteValue();
          double d = f1.doubleValue();
          System.out.println(x + b + d);
      }
      catch (NumberFormatException e) /* Line 9 */
      {
          System.out.println("bad number"); /* Line 11 */
      }
      

    • Options
    • A. 9.0
    • B. bad number
    • C. Compilation fails on line 9.
    • D. Compilation fails on line 11.
    • Discuss
    • 4. What will be the output of the program?
      String a = "newspaper";
      a = a.substring(5,7);
      char b = a.charAt(1);
      a = a + b;
      System.out.println(a);
      

    • Options
    • A. apa
    • B. app
    • C. apea
    • D. apep
    • Discuss
    • 5. Which statement is true?

    • Options
    • A. The notifyAll() method must be called from a synchronized context.
    • B. To call wait(), an object must own the lock on the thread.
    • C. The notify() method is defined in class java.lang.Thread.
    • D. The notify() method causes a thread to immediately release its locks.
    • Discuss
    • 6. Which statement is true?
      class Test1 
      {
          public int value;
          public int hashCode() { return 42; }
      }
      class Test2 
      {
          public int value;
          public int hashcode() { return (int)(value^5); }
      }
      

    • Options
    • A. class Test1 will not compile.
    • B. The Test1 hashCode() method is more efficient than the Test2 hashCode() method.
    • C. The Test1 hashCode() method is less efficient than the Test2 hashCode() method.
    • D. class Test2 will not compile.
    • Discuss
    • 7. Assuming that the equals() and hashCode() methods are properly implemented, if the output is "x = 1111", which of the following statements will always be true?
      x = 0;
      if (x1.hashCode() != x2.hashCode() )  x = x + 1;
      if (x3.equals(x4) )  x = x + 10;
      if (!x5.equals(x6) ) x = x + 100;
      if (x7.hashCode() == x8.hashCode() )  x = x + 1000;
      System.out.println("x = " + x);
      

    • Options
    • A. x2.equals(x1)
    • B. x3.hashCode() == x4.hashCode()
    • C. x5.hashCode() != x6.hashCode()
    • D. x8.equals(x7)
    • Discuss
    • 8. The static method Thread.currentThread() returns a reference to the currently executing Thread object. What is the result of this code?
      class Test 
      {
          public static void main(String [] args) 
          {
              printAll(args);
          }
      
          public static void printAll(String[] lines) 
          {
              for(int i = 0; i < lines.length; i++)
              {
                  System.out.println(lines[i]);
                  Thread.currentThread().sleep(1000);
              }
          }
      }
      

    • Options
    • A. Each String in the array lines will output, with a 1-second pause.
    • B. Each String in the array lines will output, with no pause in between because this method is not executed in a Thread.
    • C. Each String in the array lines will output, and there is no guarantee there will be a pause because currentThread() may not retrieve this thread.
    • D. This code will not compile.
    • Discuss
    • 9. Which answer most closely indicates the behavior of the program?
      public class MyProgram 
      {
          public static void throwit() 
          {
              throw new RuntimeException();
          }
          public static void main(String args[])
          {
              try 
              {
                  System.out.println("Hello world ");
                  throwit();
                  System.out.println("Done with try block ");
              }
              finally 
              {
                  System.out.println("Finally executing ");
              }
          }
      }
      

    • Options
    • A. The program will not compile.
    • B. The program will print Hello world, then will print that a RuntimeException has occurred, then will print Done with try block, and then will print Finally executing.
    • C. The program will print Hello world, then will print that a RuntimeException has occurred, and then will print Finally executing.
    • D. The program will print Hello world, then will print Finally executing, then will print that a RuntimeException has occurred.
    • Discuss
    • 10. Which two code fragments will compile?
      1. interface Base2 implements Base {}
      2. abstract class Class2 extends Base
        { public boolean m1(){ return true; }}
      3. abstract class Class2 implements Base {}
      4. abstract class Class2 implements Base
        { public boolean m1(){ return (7 > 4); }}
      5. abstract class Class2 implements Base
        { protected boolean m1(){ return (5 > 7) }}
      interface Base 
      {
          boolean m1 ();
          byte m2(short s);
      }
      

    • Options
    • A. 1 and 2
    • B. 2 and 3
    • C. 3 and 4
    • D. 1 and 5
    • Discuss


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