Java Program to Add Two Integers

The integer is stored in a variable using System.in, and is displayed on the screen using System.out.

To understand this example, you should have the knowledge of the following Java programming topics:

• Java Operators
• Java Basic Input and Output

1. Add Two Integers (Hardcoded)

In this example, we store the numbers directly in the code.

public class AddIntegers {
    public static void main(String[] args) {
        int first = 10;
        int second = 20;

        System.out.println("First Number: " + first);
        System.out.println("Second Number: " + second);

        // add two numbers
        int sum = first + second;
        System.out.println("The sum is: " + sum);
    }
}

Output:

First Number: 10
Second Number: 20
The sum is: 30

2. Add Two Integers (User Input)

Here, we use the Scanner class to take input from the user.

import java.util.Scanner;

public class AddInput {
    public static void main(String[] args) {
        // Create a Scanner object
        Scanner reader = new Scanner(System.in);

        System.out.print("Enter two numbers: ");

        // Read integers
        int first = reader.nextInt();
        int second = reader.nextInt();

        int sum = first + second;

        System.out.println("The sum is: " + sum);
        
        // Close the scanner
        reader.close();
    }
}

Output:

Enter two numbers: 10 20
The sum is: 30

Explanation

1. int first = 10;: Declares an integer variable and assigns a value.
2. Scanner reader = new Scanner(System.in);: Creates a Scanner object to read input from the standard input (keyboard).
3. reader.nextInt(): Reads the next integer from the input.
4. first + second: The + operator adds the two numbers.

Try Yourself

1. Change Values: Change the hardcoded values to 100 and 200.
2. Add Three Numbers: Modify the program to add three integers instead of two.
3. Negative Numbers: What happens if you enter -5 and 10? Try it.
4. String Concatenation: Try System.out.println("Sum: " + first + second); (without parentheses around first + second). Does it add or join?
5. Brain Twister: What happens if you try to add two very large numbers (e.g., 2000000000 + 2000000000)? Hint: Integer Overflow.