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  • Question

  • What will be the output of the program? 
    public class Test138 
{ 
    public static void stringReplace (String text) 
    {
        text = text.replace ('j' , 'c'); /* Line 5 */
    } 
    public static void bufferReplace (StringBuffer text) 
    { 
        text = text.append ("c");  /* Line 9 */
    } 
    public static void main (String args[]) 
    { 
        String textString = new String ("java"); 
        StringBuffer textBuffer = new StringBuffer ("java"); /* Line 14 */
        stringReplace(textString); 
        bufferReplace(textBuffer); 
        System.out.println (textString + textBuffer); 
    } 
}


  • Options
  • A. java
  • B. javac
  • C. javajavac
  • D. Compile error

  • Correct Answer
  • javajavac 

    Explanation
    A string is immutable, it cannot be changed, that's the reason for the StringBuffer class. The stringReplace method does not change the string declared on line 14, so this remains set to "java".

    Method parameters are always passed by value - a copy is passed into the method - if the copy changes, the original remains intact, line 5 changes the reference i.e. text points to a new String object, however this is lost when the method completes. The textBuffer is a StringBuffer so it can be changed.

    This change is carried out on line 9, so "java" becomes "javac", the text reference on line 9 remains unchanged. This gives us the output of "javajavac"

    More questions

    • 1. What will be the output of the program? 
      public class A
{ 
    void A() /* Line 3 */
    {
        System.out.println("Class A"); 
    } 
    public static void main(String[] args) 
    { 
        new A(); 
    } 
}

    • Options
    • A. Class A
    • B. Compilation fails.
    • C. An exception is thrown at line 3.
    • D. The code executes with no output.
      • Discuss
    • 2. What will be the output of the program? 
      class Test 
{
    public static void main(String [] args) 
    {
        Test p = new Test();
        p.start();
    }

    void start() 
    {
        boolean b1 = false;
        boolean b2 = fix(b1);
        System.out.println(b1 + " " + b2);
    }

    boolean fix(boolean b1) 
    {
        b1 = true;
        return b1;
    }
}

    • Options
    • A. true true
    • B. false true
    • C. true false
    • D. false false
      • Discuss
    • 3. What will be the output of the program? 
      class Test 
{
    static int s;
    public static void main(String [] args) 
    {
        Test p = new Test();
        p.start();
        System.out.println(s);
    }

    void start() 
    {
        int x = 7;
        twice(x);
        System.out.print(x + " ");
    }

    void twice(int x) 
    {
        x = x*2;
        s = x;
    }
}

    • Options
    • A. 7 7
    • B. 7 14
    • C. 14 0
    • D. 14 14
      • Discuss
    • 4. You want a class to have access to members of another class in the same package. Which is the most restrictive access that accomplishes this objective?

    • Options
    • A. public
    • B. private
    • C. protected
    • D. default access
      • Discuss
    • 5. What will be the output of the program? 
      class Super
{ 
    public int i = 0; 

    public Super(String text) /* Line 4 */
    {
        i = 1; 
    } 
} 

class Sub extends Super
{
    public Sub(String text)
    {
        i = 2; 
    } 

    public static void main(String args[])
    {
        Sub sub = new Sub("Hello"); 
        System.out.println(sub.i); 
    } 
}

    • Options
    • A. 0
    • B. 1
    • C. 2
    • D. Compilation fails.
      • Discuss
    • 6. What will be the output of the program (in jdk1.6 or above)? 
      public class BoolTest 
{
    public static void main(String [] args) 
    {
        Boolean b1 = new Boolean("false");
        boolean b2;
        b2 = b1.booleanValue();
        if (!b2) 
        {
            b2 = true;
            System.out.print("x ");
        }
        if (b1 & b2) /* Line 13 */
        {
            System.out.print("y ");
        }
        System.out.println("z");
    }
}

    • Options
    • A. z
    • B. x z

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