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Home ‣ Java Programming ‣ Inner Classes See What Others Are Saying!
  • Question

  • Which statement, inserted at line 10, creates an instance of Bar? 
    class Foo 
{
    class Bar{ }
}
class Test 
{
    public static void main (String [] args) 
    {
        Foo f = new Foo();
        /* Line 10: Missing statement? */
    }
}


  • Options
  • A. Foo.Bar b = new Foo.Bar();
  • B. Foo.Bar b = f.new Bar();
  • C. Bar b = new f.Bar();
  • D. Bar b = f.new Bar();

  • Correct Answer
  • Foo.Bar b = f.new Bar(); 

    Explanation
    Option B is correct because the syntax is correct-using both names (the enclosing class and the inner class) in the reference declaration, then using a reference to the enclosing class to invoke new on the inner class.

    Option A, C and D all use incorrect syntax. A is incorrect because it doesn't use a reference to the enclosing class, and also because it includes both names in the new.

    C is incorrect because it doesn't use the enclosing class name in the reference variable declaration, and because the new syntax is wrong.

    D is incorrect because it doesn't use the enclosing class name in the reference variable declaration.

    • More questions

    • 1. What will be the output of the program? 
      public class Test 
{
    public static void main(String [] args) 
    {
        signed int x = 10;
        for (int y=0; y<5; y++, x--)
            System.out.print(x + ", ");
    }
}

    • Options
    • A. 10, 9, 8, 7, 6,
    • B. 9, 8, 7, 6, 5,
    • C. Compilation fails.
    • D. An exception is thrown at runtime.
      • Discuss
    • 2. Which two of the following statements, inserted independently, could legally be inserted into missing section of this code?
      1. boolean test = (Component instanceof t);
      2. boolean test = (t instanceof Ticker);
      3. boolean test = t.instanceof(Ticker);
      4. boolean test = (t instanceof Component);
          
import java.awt.*;
class Ticker extends Component 
{
    public static void main (String [] args) 
    {
        Ticker t = new Ticker();
        /* Missing Statements? */
    }
}

    • Options
    • A. 1 and 4
    • B. 2 and 3
    • C. 1 and 3
    • D. 2 and 4
      • Discuss
    • 3. What will be the output of the program? 
      class Test 
{
    public static void main(String [] args) 
    {
        int x=20;
        String sup = (x < 15)? "small" : (x < 22)? "tiny" : "huge";
        System.out.println(sup);
    }
}

    • Options
    • A. small
    • B. tiny
    • C. huge
    • D. Compilation fails
      • Discuss
    • 4. Which statement, inserted at line 10, creates an instance of Bar? 
      class Foo 
{
    class Bar{ }
}
class Test 
{
    public static void main (String [] args) 
    {
        Foo f = new Foo();
        /* Line 10: Missing statement? */
    }
}

    • Options
    • A. Foo.Bar b = new Foo.Bar();
    • B. Foo.Bar b = f.new Bar();
    • C. Bar b = new f.Bar();
    • D. Bar b = f.new Bar();
      • Discuss
    • 5. What line of code should replace the missing statement to make this program compile? 
      /* Missing Statement? */
public class foo 
{
    public static void main(String[]args)throws Exception 
    {
        java.io.PrintWriter out = new java.io.PrintWriter(); 
        new java.io.OutputStreamWriter(System.out,true); 
        out.println("Hello"); 
    } 
}

    • Options
    • A. No statement required.
    • B. import java.io.*;
    • C. include java.io.*;
    • D. import java.io.PrintWriter;
      • Discuss
    • 6. When is the B object, created in line 3, eligible for garbage collection? 
      void start() {  
    A a = new A(); 
    B b = new B(); 
    a.s(b);  
    b = null; /* Line 5 */
    a = null;  /* Line 6 */
    System.out.println("start completed"); /* Line 7 */
}

    • Options
    • A. after line 5
    • B. after line 6
    • C. after line 7
    • D. There is no way to be absolutely certain.
      • Discuss
    • 7. Which is a reserved word in the Java programming language?

    • Options
    • A. method
    • B. native
    • C. subclasses
    • D. reference
    • E. array
      • Discuss
    • 8. Which statement is true for the class java.util.ArrayList?

    • Options
    • A. The elements in the collection are ordered.
    • B. The collection is guaranteed to be immutable.
    • C. The elements in the collection are guaranteed to be unique.
    • D. The elements in the collection are accessed using a unique key.
      • Discuss
    • 9. What will be the output of the program? 
      public class Test 
{ 
    public static void main(String[] args) 
    {
        final StringBuffer a = new StringBuffer(); 
        final StringBuffer b = new StringBuffer(); 

        new Thread() 
        { 
            public void run() 
            {
                System.out.print(a.append("A")); 
                synchronized(b) 
                { 
                    System.out.print(b.append("B")); 
                } 
            } 
        }.start(); 
            
        new Thread() 
        {
            public void run() 
            {
                System.out.print(b.append("C")); 
                synchronized(a) 
                {
                    System.out.print(a.append("D")); 
                } 
            } 
        }.start(); 
    } 
}

    • Options
    • A. ACCBAD
    • B. ABBCAD
    • C. CDDACB
    • D. Indeterminate output
      • Discuss
    • 10. Which is true about a method-local inner class?

    • Options
    • A. It must be marked final.
    • B. It can be marked abstract.
    • C. It can be marked public.
    • D. It can be marked static.
      • Discuss

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