Summary: In this programming example, we will learn different ways to calculate the sum of first n even numbers in Java.

## Method 1: Using For Loop

``````import java.util.Scanner;

public class Main
{
public static void main(String[] args) {
Scanner in= new Scanner(System.in);

System.out.print("Enter the value of n: ");
int n = in.nextInt();

int sum=0, num = 1;

for(int count=1; count<=n; ){
//if num is even then increment 'count'
if(num%2 == 0){
sum += num;
count++;
}
num++;
}

System.out.println("Sum: "+sum);
}
}``````

Output:

Enter the value of n: 3
Sum: 12

In the above program, we have used the `count` as the loop variable.

The `count` variable stores the count of the even numbers that have been added to the `sum`.

The `num` variable is the natural number which we test and increment in each iteration.

When the value of the `count` equals `n`, it means we have successfully added first n even numbers.

## Method 2: Using while Loop

``````import java.util.Scanner;

public class Main
{
public static void main(String[] args) {
Scanner in= new Scanner(System.in);

System.out.print("Enter the value of n: ");
int n = in.nextInt();

int sum=0, num = 1, count=0;

while(count<n){
//if num is even then increment 'count'
if(num%2 == 0){
sum += num;
count++;
}
num++;
}

System.out.println("Sum: "+sum);
}
}``````

Output:

Enter the value of n: 10
Sum: 110

The logic used in this method is the same as the above program, only we have replaced for loop with a while loop.

The while loop runs until count != n.

## Method 3: Using Formula

We can easily compute the sum of first n even numbers using the formula n*(n+1).

Let’s use it in our program to output the sum of the first 100 even numbers.

``````import java.util.Scanner;

public class Main
{
public static void main(String[] args) {
Scanner in= new Scanner(System.in);

System.out.print("Enter the value of n: ");
int n = in.nextInt();

int sum= n*(n+1);

System.out.println("Sum: "+sum);
}
}``````

Output:

Enter the value of n: 100
Sum: 10100

Note: The above programs compute the sum of first n even numbers. They don’t calculate the sum of even numbers from 1 to n.