JavaProgrammingWorld.com

QUESTION : 1

   Any class that implements the Runnable interface
   has to provide the implementation for the following methods
    public void start();
    public void run();

1. True.
2. False.

ANS : 2

QUESTION : 2

     True or false ?      

       A thread that has called the wait() method of an  object
    still owns the lock of the object.

1. True
2. False

ANS : 2

QUESTION : 3

      A number of threads of the same priority  have relinquished the lock
    on a monitor and are in a waiting state after having called the wait()
    method of the object. A new thread enters the monitor and calls the
    notifyAll() method of the meonitor. Which of these threads will be the
    first one to resume? 

1. The thread that has been waiting the longest.
2. The thread that was the last one to to exit the monitor.
3. You can never be sure which thread will get to run first.
4. The the first thread that called the wait() method

ANS : 3

QUESTION : 4

     Which of these are valid contructors of a Thread object.

1. public Thread(Object obj)
2. public Thread(String name)
2. public Thread(Runnable trgt)
4. public Thread(ThreadGroup grp, Runnable trgt, String name)
5. public Thread(ThreadGroup grp, Object ob)

ANS : 2,3,4

QUESTION : 5

    If you call  the interrupted() method of a thread object twice
    the second call will always return false.  

1. True
2. False

ANS : 1

QUESTION : 6

         If you call  the isInterrupted() method of a thread object twice
         the second call will always return false. 

1. True
2. False

ANS : 2

QUESTION : 7

      Which of the following are methods of the Thread class.

1. public void run()
2. public void start()
3. public void exit()
4. public final void setAccess()
5. public final void setPriority(int priNbr)
6. public final int getPriority() 

ANS : 1,2,5,6

QUESTION : 8

   Consider the following class
      public class Test implements Runnable{
      public void run(){}
      }
   True or False ?
   Creating an instance of this class and calling its run() method
   will spawn a new thread.   

1. True
2. False

ANS : 2

QUESTION : 9

       True or false?
       A Thread object has a method called notify().

1. False
2. True

ANS : 2

  The Thread class has a method notify() inherited from Object.  

QUESTION : 10

  Calling the destroy() method of a thread object relases all the locks held by
    the thread ?

1. True
2. False 

ANS : 2

QUESTION : 1

   What is the result of attempting to compile and run the following code?

  public class Test1{
     public static void main(String[] args)
     {
     Integer int1 = new Integer(10);
     Vector vec1 = new Vector();
     LinkedList list = new LinkedList();
     vec1.add(int1);
     list.add(int1);
     if(vec1.equals(list)) System.out.println("equal");
     else  System.out.println("not equal");
      }
  } 

1. The code will fail to compile.
2. Runtime error due to incompatible object comparison
3. Will run and  print "equal".
4. Will run and  print "not equal".

ANS : 3

        correct answer/s : 3 

QUESTION : 2

   What is the result of attempting to compile and run the following code?
           public class Test {

              public static void main(String[] args){
               Integer a = new Integer(4);
               Integer b = new Integer(8);
               Integer c = new Integer(4);
               HashSet hs = new HashSet();
               hs.add(a);
               hs.add(b);
               hs.add(c);
               System.out.println(hs);
              }
         }

1. Will print [8, 4]
2. Will print [4, 8, 4]
3. Will print [8, 4, 4]

ANS : 1

        correct answer/s : 1

QUESTION : 3

   What is the result of attempting to compile and run the following code?
           public class Test {

              public static void main(String[] args){
               Integer a = new Integer(4);
               Integer b = new Integer(8);
               Integer c = new Integer(4);
               TreeSet hs = new TreeSet();
               ts.add(a);
               ts.add(b);
               ts.add(c);
               System.out.println(ts);
              }
         }

1. Will print [8, 4]
2. Will print [4, 8, 4]
3. Will print [8, 4, 4]
4. Will print [4, 8]
5. Will print [4, 4, 8]

ANS : 4

       correct answer/s : 4

QUESTION : 4

     What will this print out ?

           public class Test {

              public static void main(String[] args){
               Integer a = new Integer(8);
               Integer b = new Integer(4);
               Integer c = new Integer(4);
               Vector vec = new Vector();
               Iterator itr;
               vec.add(a);
               vec.add(b);
               vec.add(c);
               itr = vec.iterator();
                  while (itr.hasNext()) {
                   System.out.println("" + itr.next());
                  }
              }
         }

1.  8 , 4 and 4
2.  4 , 4 and 8
3.  8 and 4
4.  4 and 8

ANS : 1

       correct answer/s : 1

QUESTION : 5

   Which of these statements are true?

1. HashTable is a sub class of Dictionary
2. ArrayList is a sub class of Vector
3. LinkedList is a subclass of ArrayList
4. Stack is a subclass of Vector

ANS : 1,4

       correct answer/s : 1,4

QUESTION : 6

   Which of these statements are true? 

1. LinkedList extends List
2. AbstractSet extends Set
3. HashSet extends AbstractSet
4. WeakHashMap extends HashMap
5. TreeSet extends AbstractSet

ANS : 3,5

       correct answer/s : 3,5

QUESTION : 7

    Which of these statements are true? 

1. A HashSet does not permit duplicates
2. A Vector permits duplicates
3. A TreeSet is an ordered Set
4. A LinkedList is sorted in descending order
5. A LinkedList is sorted in ascending order 

ANS : 1,2,3

       correct answer/s : 1,2,3

QUESTION : 8

      True or False.
     A WeakHashMap is synchronized.

1. True
2. False

ANS : 2

       correct answer/s : 2

QUESTION : 9

      True or False.
     A Set rejects duplicates and is ordered

1. True
2. False

ANS : 2

       correct answer/s : 2

QUESTION : 10

     Select the true statements

1. AbstractSet extends AbstractCollection
2. AbstractList extends AbstractCollection
3. HashSet extends AbstractSet
4. Vector extends AbstractList
5. AbstrctSequentialList extends AbstractList
6. LinkedList extends AbstrctSequentialList

ANS : 1,2,3,4,5,6

       correct answer/s : 1,2,3,4,5,6

QUESTION : 1

  What will be the result of compiling and running the following code?
   import java.awt.*;
   import java.applet.*;
   public class AppletTest extends Applet {
     Label lbl = new Label("hello");
      public void init()
      {
      setSize(200,100);
      setVisible(true);
      lbl.setBackground(new Color(0,100,180));
      setLayout(new GridLayout(1,1));
      add(lbl);
      setLayout(new FlowLayout());
      lbl.setBounds(0,0,100,24);
      }
   }

1. The label will fill half the display area of the applet.
2. The label will be wide enough to display the text "hello"
3. The label will not be visiblle.
4. The label will fill the entire display area of the applet
5. The code will throw a run time error because of the second setLayout() call.

ANS : 2

QUESTION : 2

   What will be the result of compiling and running the following applet?
   import java.awt.*;
   import java.applet.*;
   public class AppletTest extends Applet {
      public void init()
      {
      super.init();
      PanelTest p = new PanelTest();
      p.init();
      setVisible(true);
      setSize(200,100);
      add(p);
   }

   class PanelTest extends Panel{
      Button b1 = new Button("Press me");
      public PanelTest()
      {
      setSize(200,100);
      setVisible(true);
      }
      public void init(){
      super.init();
      add(b1);
      }
     }
   }

1. The button will fill the entire display area of the applet.
2. The code will fail to compile.
3. The button will be just big enough to encompass it's label.
4. The applet's display area will be blank.

ANS : 2

QUESTION : 3
This code compiles without error.
class MyButton extends Button implements MouseListener{
 public MyButton(String lbl) {
   super(lbl);
   addMouseListener(this);
 }
 public void mousePressed(MouseEvent e){
 //do something
  }
}

1. False
2. True

ANS : 1

QUESTION : 4

    Which of the following are valid constructors for a TextField .

1. TextField();
2. TextField(int rows , int cols);
3. TextField(int cols , String txt);
4. TextField(int cols);
5. TextField(String txt , boolean scrollBars);

ANS : 1,4

QUESTION : 5

      True or false?
       void setResizable(boolean) is a member of the Applet class.

1. True
2. False

ANS : 2

QUESTION : 6

   What is the result of attempting to compile and run the following.
     import java.awt.*;
     import java.awt.event.*;
     class FrameTest extends Frame{
        Label lblTest  = new Label("TEST");
        Button btnTest = new Button(" TEST ");
        public static void main(String[] args){
          FrameTest ft = new FrameTest();
          ft.setLayout(new FlowLayout());
          ft.add(ft.lblTest);
          ft.add(ft.btnTest);
          ft.setSize(200,100);
          ft.setVisible(true);
          ft.enableEvents(AWTEvent.ACTION_EVENT_MASK);
        }
       public void processActionEvent(ActionEvent event){
          super.processActionEvent(event);
            if(event.getID() == AWTEvent.ACTION_EVENT_MASK){
              if(event.getSource() instanceof Button){
               lblTest.setText("OK");
               }
            }
        }
     }

1. The code will not compile
2. There will be a runtime error
3. The frame wil not be visible
4. Nothing happens when you click the button
5. The label's caption changes to "OK" when you click the button

ANS : 1

QUESTION : 7

  What is the default layout for a Dialog ?

1. FlowLayout
2. GridLayout
3. CardLayout
4. BorderLayout
5. GridBagLayout

ANS : 4

QUESTION : 8

     True or false.
      A Dialog is a subclass of Frame. 

1. True
2. False

ANS : 2

QUESTION : 9

  Which of the following are valid constructors for a MenuItem ?

1. MenuItem()
2. MenuItem(String name)
3. MenuItem(String name , boolean removable)
4. MenuItem(String name , MenuShortcut sc)
5. MenuItem(boolean check)

ANS : 1,2,4

QUESTION : 10

      What will this draw ?
     public class AppletTest extends Applet{
     public void init(){
     setVisible(true);
     setSize(200,200);
     }
     public void paint(Graphics g){
     g.setColor(new Color(0,0,255));
     g.drawRect(50, 100 , 100, 50);
     }
    }

1. A rectangle 50 pixels wide with top left corner at 100, 50.
2. A rectangle 50 pixels wide with top left corner at 50,100.
3. A rectangle 100 pixels wide with top left corner at 50,100.
4. A rectangle 100 pixels high with top left corner at 50,100.
5. A rectangle 100 pixels high with top left corner at 100,50. 

ANS : 3

QUESTION : 1

 What is the result of compiling and running this program?

      class Mammal{
         void eat(Mammal m){
         System.out.println("Mammal eats food");
         }
      }
      class Cattle extends Mammal{
         void eat(Cattle c){
         System.out.println("Cattle eats hay");
         }
      }

      class Horse extends Cattle{
          void eat(Horse h){
          System.out.println("Horse eats hay");
          }
      }
      public class Test{
        public static void main(String[] args){
          Mammal h = new Horse();
          Cattle c = new Horse();
          c.eat(h);
        }
      }

1. prints "Mammal eats food"
2. prints "Cattle eats hay"
3. prints "Horse eats hay"
4. Class cast Exception at runtime.

ANS : 1

    The method that will be called is the one
    from class Mammal. The reasons are quite obvious.

QUESTION : 2

 Comsider the following class hierarchy.
1. interface A{
2. public void method1();
3. }
4. class One implements A{
5. public void method1(){
6. System.out.println("hello");
7. }
8. }
9. class Two extends One{}
10. public class Test extends Two{
11. public static void main(String[] args)
12. {
13. A a;
14. Two t = new Two();
15. a = t;
16. a.method1();
17. }
18. }
What will be the outcome on attempting to compile and run this ?

1. Compiles and runs printing out "hello".
2. Compilation error at line 16.
3. The compiler raises an objection to the assignment at line 15.
4. Throws a NoSuchMethodException at runtime.  

ANS : 1

    Object reference conversion is possible here.
    The old type which is class can be assigned
    to an interface type as long as the class implements
    that interface.

QUESTION : 3
  What will happen if you try to compile and run this ?
 interface A{
 public void innerMeth();
 }
        public class Test {
   A a;
   int memVar = 1;
          void aMethod(){
                 a = new A(){
                 public void innerMeth(){
                 System.out.println(memVar);
                 } };
    }

           public static void main(String[] args){
            Test t = new Test();
             t.a.innerMeth();
            }
          }

1. Compiler error.
2. NoSuchMethodException at runtime.
3. Compiles and runs printing 1
4. Throws a NullPointerException at runtime.

ANS : 4
     You will get a NullPointerException because the
     inner class object gets assigned to the reference a
     only after the aMethod() runs. You can prevent
     the exception by calling t.aMethod() before the
     inner anonymous class method is called.

QUESTION : 4

       What will happen if you try to compile and run this code.

         class Rectangle{
           public int area(int length , int width) {
             return  length * width;
           }
          }

         class Square extends Rectangle{
            public int area(long length , long width) {
            return  (int) Math.pow(length ,2);
           }
         }
        class Test{
          public static void main(String args[]) {
           Square r = new Square();
           System.out.println(r.area(5 , 4));
          }
        }

1. Will not compile.
2. Will compile and run printing out 20
3. Runtime error
4. Will compile and run printing out 25

ANS : 1

    This code will fail to compile because the
    compiler cannot resolve the method call here.

QUESTION : 5

   What will be the result of attempting to compile and run this.

     class Base{}
     class Derived extends Base{}
     public class Test {
       public static void main(String[] args){
         Derived d = (Derived) new Base();
       }
     }

1. Will not compile
2. Compiles and runs without error.
3. Runtime error

ANS : 3

QUESTION : 6

   What will this program print out ?
      class Base{
        int value = 0;
        Base(){
        addValue();
        }
        void addValue(){
        value += 10;
        }
       int getValue(){
         return value;
       }
     }
    class Derived extends Base{
      Derived(){
       addValue();
      }
     void addValue(){
     value +=  20;
      }
    }
    public class Test {
      public static void main(String[] args){
          Base b = new Derived();
          System.out.println(b.getValue());
      }
    }

1. 10
2. 20
3. 30
4. 40

ANS : 4

QUESTION : 7

   Almost the same code as in the previous question.
   The only difference is the methods are static now.
   What will it print now?

   class Base{
      static  int value = 0;
        Base(){
        addValue();
        }
    static void addValue(){
        value += 10;
        }
       int getValue(){
         return value;
       }
     }
    class Derived extends Base{
      Derived(){
       addValue();
      }
    static void addValue(){
     value +=  20;
      }
    }
    public class Test {
      public static void main(String[] args){
          Base b = new Derived();
          System.out.println(b.getValue());
      }
    }

1. 10
2. 20
3. 30
4. 40

ANS : 3

QUESTION : 8

     What is the result of attempting to compile and run this ?
      interface ITest{
           public void setVal();
      }
      public class Test {
          private String a;
          void aMethod(){
          final String b;
          ITest it = new ITest() {
               public void setVal(){
               a = "Hello";
               b = " World";
               }};
          it.setVal();
          System.out.println(a + b);
          }
          public static void main(String[] args) {
          Test t = new Test();
          t.aMethod();
          }
       }

1. Code will not compile
2. Run time error
3. Will compile and run printing "Hello"
4. Will compile and run without any output

ANS : 1

QUESTION : 9

   What is the result of attempting to compile and run this ?

         class Base{
              String s = "Base";
              String show(){
              return s;
              }
         }
         class Derived extends Base{
              String s = "Derived";
              }
         public class Test {
              void print(Base b){
              System.out.println(b.show());
              }
              void print(Derived d){
              System.out.println(d.show());
              }
              public static void main(String[] args){
              Test t = new Test();
              Base b = new Derived();
              t.print(b);
              }
         }

1. Code will not compile
2. Run time error
3. Will compile and run printing "Derived"
4. Will compile and run printing "Base"

ANS : 4

QUESTION : 10

   What is the result of attempting to compile and run this ?
    interface ITest{
     public void setVal();
    }
    public class Test {
      private String a;
      void aMethod(){
      final String b = " World";
      ITest it = new ITest() {
                   public void setVal(){
                   a = "Hello" + b;
                   }};
      it.setVal();
      System.out.println(a);
      }
      public static void main(String[] args) {
      Test t = new Test();
      t.aMethod();
      }
    }

1. Code will not compile
2. Run time error
3. Will compile and run printing "Hello World"
4. Will compile and run printing "Hello"

ANS : 3

QUESTION1

  You have the following code in a file called Test.java

    class Base{
       public static void main(String[] args){
       System.out.println("Hello");
       }
    }

    public class Test extends Base{}

   What will happen if you try to compile and run this?

1. It will fail to compile.
2. Runtime error
3. Compiles and runs with no output.
4. Compiles and runs printing "Hello"

ANS : 4

 This will compile and print "Hello"
 The entry point for a standalone java program is
 the main method of the class that is being run.
 The java runtime system will look for that method
 in class Test and find that it does have such a method.
 It does not matter whether it is defined in the class itself
 or is inherited from a parent class.   

QUESTION2

         What is the result of trying to compile and run the following code.
         public final static void main(String[] args){
         double d = 10.0 / -0;
          if(d == Double.POSITIVE_INFINITY)
           System.out.println("Positive infinity");
           else
           System.out.println("Negative infinity");
         }

1. output Positive infinity
2. output Negative infinity
3. Will fail to compile
4. Runtime exception

ANS : 1

    There is no such thing as a positive or negative zero.
    Hence the result is always positive infinity.

QUESTION3

   What is the result that will be printed out ?
     void aMethod()
     {
     float f = (1 / 4) * 10;
     int i = Math.round(f);
     System.out.println(i);
     }

1.    2
2.    0
3.    3
4.    2.5
5.    25

ANS : 2

   The result of 1/4 will be zero because integer
   divion is carried out on the operands.
   If you need to obtain a fractional value
   you need to use either a float or double literal
   as in 1F / 4F.

QUESTION4

  Which of the following are valid declarations?

   Note : None of the literals used here
          contain the character O they are all zeroes.

1. int i     = 0XCAFE;
2. boolean b = 0;
3. char c    = 'A';
4. byte b    = 128;
5. char c    = "A";

ANS : 1,3

   1. is correct as it is a valid hexadecimal number.2. is  wrong
   because you can only assign the values true and false to them
   4 is wrong because 128 is beyond the range of a byte. 5is wrong
   because "A" is not a char it is a String. 

QUESTION5

  What is the result of trying to compile and run this program.
    public class Test{
       public static void main(String[] args){
        int[] a = {1};
        Test t = new Test();
        t.increment(a);
        System.out.println(a[a.length - 1]);
       }
       void increment(int[] i){
       i[i.length - 1]++;
       }
    }

1. Compiler error.
2. Compiles and runs printing out 2
3. Compiles and runs printing out 1
4. An ArrayIndexOutOfBounds Exception at runtime

ANS : 2

  You are passing a reference to an array as
  the argument to the method. The method may not
  modify the passed object reference but it can modify
  the object itself.  

QUESTION6

   What will happen if you try to compile and run this ?
   public class Test{
      static{
       print(10);
       }
     static void print(int x){
       System.out.println(x);
       System.exit(0);
      }
    }

1. Compiler error.
2. Will throw a NoSuchMethod error at runtime.
3. It will compile and run printing out "10"
4. It will run with no output.
5. It will run and print "10" and then crash with an error.      

ANS : 3

    This will run, print a message and terminate gracefully.
    The runtime system needs to load the class before it can look
    for the main method. So the static initializer will run first
    and print "10". Immediately after that System.exit(0) will be called
    terminating the program before an error can be thrown. 

QUESTION7

      Is this legal?
      long longArr[];
      int intArr[] = { 7 ,8 , 9};
      longArr = intArr;

1. Yes
2. No

ANS : 2

   You cannot assign a reference to an array of primitives
   to another unless they contain the same primitive types. 

QUESTION8

   True or False.
   The range of a byte is from  -127 to 128

1. True
2. False

ANS : 2

   Correct answer/s : 2
   The statement is false. The range of an array
   is from  - 128 to 127 

QUESTION9

   Identify the valid assignments.

1. float f  = \u0038;
2. long L2 = 2L;
3. float f  = 1.2;
4. char c = '/u004E';
5. byte b = 100;

ANS : 1,2,4,5

    1 is correct because \u0038 is unicode for nbr 8.
    3 is wrong because 1.2 is a double literal.
    4. is a little sneaky perhaps. The
       unicode escape character is incorrect

QUESTION10

        What is the result of trying to compile and run the following code.
         public static void main(String[] args){
         double d = 10 / 0;
         if(d == Double.POSITIVE_INFINITY)
           System.out.println("Positive infinity");
         else
           System.out.println("Negative infinity");
         }

1. output Positive infinity
2. output Negative infinity
3. Will fail to compile
4. Runtime exception

ANS : 4

   Division by zero on integer literals will throw
   a runtime error.

QUESTION : 1

     What is the result of attempting to compile and run this ?
         public class Test {
              public static void main(String[] args){
              String s = "HelloWorld".substring(5,10);
              System.out.println(s);
              }
         }

1. The code will fail to compile.
2. Compile and run printing out "orld".
3. Compile and run printing out "oworl"
4. Compile and run printing out "World"
5. Run time exception

ANS : 4

QUESTION : 2

  Select one right answer.
  -----------------------
   What is the result of attempting to compile and run this ?
   1.	public class Test {
   2.     public static void main(String[] args){
   3.      Test t = new Test();
   4.      char c = 4 * 4;
   5.      String s = "bead";
   6.      s = t.pearl(s);
   7.      System.out.println(Byte.parseByte(s,c));
          }
   8.     String pearl(String s){
   9.      return s.substring(0,1);
          }
        }

1. Compiler error caused by line 4.
2. Compiler error caused by line 7.
3. Compiler error caused by line 9.
4. Compiles and throws a NumberFormatException at runtime.
5. Compiles and runs printing out a number.
6. Compiles and runs printing out an alphabet.

ANS : 5
   1. Is wrong because it is legal to assign integer
      literal to a char variable as long as the value
      does not exceed the range of a char.
   2. Is wrong because parseByte(String s , int radix)
      will accept any native numeric type that is not
      wider than an int.
   3  and 6 are just nonsense.
   4. Is wrong because the the character b falls within
      the radix range specified by the second parameter.

QUESTION : 3

   What is the value of d that will be printed out.

    public class Test {
      public final static void main(String[] args)
      {
      double d = - 22.22222;
      System.out.println(Math.ceil(d));
      }
    }

1.  22
2.  22.0
3. -22
4. -23
5. -22.0
6.  23.0

ANS : 5

QUESTION : 4

    What is the result of attempting to compile and run this ? 

    public class Test {
      public static void main(String[] args)
      {
      StringBuffer a =  "Hello";
      StringBuffer b = a.append("World");
      System.out.println(a);
      }
    }

1.  It will print "World"
2.  It will print "HelloWorld"
3.  It will print "Hello World"
4.  The code will not compile.
5.  It will print "Hello"
6.  It will throw a runtime exception

ANS : 4

QUESTION : 5

      Which of the follwing are valid methods of the String class.

1. String append(String s);
2. int length();
3. String toString(String str);
4. String trim();
5. int indexOf(int ch);
6. String append(char c);

ANS : 2,4,5

QUESTION : 6

    What is the result of attempting to compile and run this ? 

    public class Test {
      public static void main(String[] args)
      {
      Float f = new Float(32D);
      System.out.println(f);
      }
    }

1. Does not compile
2. Compiles and runs printing out "32"
3. Compiles and runs printing out "32.0"
4. Compiles but throws an error at runtime

ANS : 3

QUESTION : 7

    What is the result of attempting to compile and run this ? 

         public class Test {

              public static void main(String[] args){
               byte a = 10;
               Byte b    = new Byte(a);
               Byte c    = new Byte(11);
               System.out.println(b.compareTo(c));
              }
         }

1. Compiler error
2. Runtime error
3. Runs and prints "false"
4. Runs and prints "0"
5. Runs and prints "1"
6. Runs adn prints "-1"

ANS : 1

       correct answer/s : 1

QUESTION : 8

    What is the result of attempting to compile and run this ?
         public class Test {

              public static void main(String[] args){
               Float f = new Float(16/0);
               System.out.println(f.isNaN());
              }
         }

1. Compiler error
2. Runtime error
3. Runs and prints "false"
4. Runs and prints "true"

ANS : 2

QUESTION : 9
          What is the result of attempting to compile and run this ? 

         public class Test {

              public static void main(String[] args){
               Number n = new Number(16);
               Float f  = new Float(16);
               System.out.println(n.equals(f));
              }
         }

1. Compiler error
2. Runtime error
3. Runs and prints "false"
4. Runs and prints "true"

ANS : 1

QUESTION : 10

    What is the result of attempting to compile and run this ?
         public class Test {

              public static void main(String[] args){
              Integer i  = new Integer(256);
              System.out.println(i.byteValue());
              }
         }

1. Compiler error
2. Runtime error
3. Runs and prints "256"
4. Runs and prints "0"
5. Runs and prints "127"

ANS : 4