Question:

public class ScopeLifetimeVariables {

    public static void main(String[] args) {
        int x = 5;
        int result = multiplyByTwo(x);
        
        System.out.println(result);
    }
    
    public static int multiplyByTwo(int num) {
        int temp = num;
        num = num * 2;
        return num;
    }
}

What will be the output of the above Java program?

A) 5 B) 10 C) 15 D) It will result in a compile-time error.

Explain your answer and also discuss the scope and lifetime of the variables used in the program.

Answer:

The output of the above program will be:

10

Explanation:

The program begins by declaring and initializing an integer variable x with the value 5. Then, it calls the multiplyByTwo method passing the value of x as an argument.

Inside the multiplyByTwo method, a local variable num is declared and initialized with the value passed as an argument. In this case, num will have the value 5.

A temporary local variable temp is declared and assigned the value of num, which is 5 in this case.

The program then multiplies the value of num by 2 and assigns the updated value to num. So, num becomes 10.

Finally, the method returns the value of num which is then stored in the result variable in the main method.

The value of result, which is 10, is then printed using the System.out.println statement, resulting in the output 10.

Scope and Lifetime of Variables:

• The variable x declared in the main method has a scope limited to the main method, hence it cannot be accessed outside this method.
• The variable result also has a scope limited to the main method, and its lifetime is until the end of the main method.
• The parameter num in the multiplyByTwo method has a scope limited to the multiplyByTwo method. It's a local variable accessible only within the method. Its lifetime is until the method finishes executing.
• The variable temp is also a local variable within the multiplyByTwo method, with a limited scope and lifetime within the method. It ceases to exist after the method finishes executing.
• The temporary variable num created in the multiplyByTwo method shadows the num parameter. It is specific to the method and has no impact on other parts of the program.