Exercise: Declarations And Access Control

Questions for: Declarations And Access Control

What will be the output of the program? 
public class Test 
{
    public int aMethod()
    {
        static int i = 0;
        i++;
        return i;
    }
    public static void main(String args[])
    {
        Test test = new Test();
        test.aMethod();
        int j = test.aMethod();
        System.out.println(j);
    }
}
A:
0
B:
1
C:
2
D:
Compilation fails.
Answer: D

Compilation failed because static was an illegal start of expression - method variables do not have a modifier (they are always considered local).

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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); 
    } 
}
A:
0
B:
1
C:
2
D:
Compilation fails.
Answer: D

A default no-args constructor is not created because there is a constructor supplied that has an argument, line 4. Therefore the sub-class constructor must explicitly make a call to the super class constructor: 

public Sub(String text)
{ 
    super(text); // this must be the first line constructor 
    i = 2; 
}
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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(); 
    } 
}
A:
Class A
B:
Compilation fails.
C:
An exception is thrown at line 3.
D:
The code executes with no output.
Answer: D

Option D is correct. The specification at line 3 is for a method and not a constructor and this method is never called therefore there is no output. The constructor that is called is the default constructor.

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What will be the output of the program? 
public class Test 
{  
    public static void main(String args[])
    { 
        class Foo 
        {
            public int i = 3;
        } 
        Object o = (Object)new Foo();
        Foo foo = (Foo)o;
        System.out.println("i = " + foo.i);
    }
}
A:
i = 3
B:
Compilation fails.
C:
i = 5
D:
A ClassCastException will occur.
Answer: A
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What will be the output of the program? 
class A 
{
    final public int GetResult(int a, int b) { return 0; } 
} 
class B extends A 
{ 
    public int GetResult(int a, int b) {return 1; } 
} 
public class Test 
{
    public static void main(String args[]) 
    { 
        B b = new B(); 
        System.out.println("x = " + b.GetResult(0, 1));  
    } 
}
A:
x = 0
B:
x = 1
C:
Compilation fails.
D:
An exception is thrown at runtime.
Answer: C

The code doesn't compile because the method GetResult() in class A is final and so cannot be overridden.

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