Java final keyword

Question 1

What is the use of final keyword in Java?

• A. When a class is made final, a subclass of it can not be created.
• B. When a method is final, it can not be overridden.
• C. When a variable is final, it can be assigned value only once.
• D. All of the above

Answer: (D)

See final in Java.

Question 2

Output of following Java program

class Main {
 public static void main(String args[]){
   final int i;
   i = 20;
   System.out.println(i);
 }
}

• A. 20
• B. Compiler Error
• C. 0
• D. Garbage value

Answer: (A)

There is no error in the program. final variables can be assigned value only once. In the above program, i is assigned a value as 20, so 20 is printed.

Question 3

class Main {
 public static void main(String args[]){
    final int i;
    i = 20;
    i = 30;
    System.out.println(i);
 }
}

• A. 30
• B. Compiler Error
• C. Garbage value
• D. 0

Answer: (B)

i is assigned a value twice. Final variables can be assigned values only one. Following is the compiler error "Main.java:5: error: variable i might already have been assigned"

Question 4

class Base {
  public final void show() {
       System.out.println("Base::show() called");
    }
}
class Derived extends Base {
    public void show() {  
       System.out.println("Derived::show() called");
    }
}
public class Main {
    public static void main(String[] args) {
        Base b = new Derived();;
        b.show();
    }
}

• A. Derived::show() called
• B. Base::show() called
• C. Compiler Error
• D. Exception

Answer: (C)

compiler error: show() in Derived cannot override show() in Base