In the previous article, we have discussed about Java Program to Find the Sum of Series (a*2) + (a*3) + (a*4) + …… + N

In this article we are going to see how to find sum of the series 2-4+6-8+…-/+N by using Java programming language

## Java Program to Find the Sum of Series 2-4+6-8+…-/+N

On observing the pattern carefully, we can see first number is positive and second number is negative.

While 1^{st} number starts with 2, 2^{nd} number is 2 added with previous number.

**Example:**

X = 2

N = 20

2 – 4 + 6 – 8 + …… – 20 = -10

Let’s see different ways to find sum of the series 2-4+6-8+…-/+N.

### Method-1: Java Program to Find the Sum of Series 2-4+6-8+…-/+N By Using For Loop

**Approach:**

- Declare an integer variable say ‘
`n`

’ which holds the last term of the series. - Create Scanner class object.
- Prompt the user to enter a number as value of
`n`

. - Declare an integer variable say ‘
`sum`

‘and initialize it with 0. - Use a for loop
`from i =1 to i<=n/2`

- Inside for loop we will first check the index of
`i`

, if`i`

is even then we will subtract`i*2`

from`sum`

Else we will add`i*2`

in sum.

- Print the result.

**Program:**

import java.util.*; public class Main { public static void main(String args[]) { //creating object of Scanner class Scanner s = new Scanner(System.in); //Taking input of number of elements in the series System.out.println("Enter the value of last number 'n' "); int n = s.nextInt(); //for loop to print the series int sum = 0; for (int i = 1; i <= n/2; i++) { if (i % 2 == 0) sum -= i * 2; else sum += i * 2; } System.out.println("Sum of the series is " + sum); } }

Output: Enter the value of last number 'n' 20 Sum of the series is -10

### Method-2: Java Program to Find the Sum of Series 2-4+6-8+…-/+N By Using While Loop

**Approach:**

- Declare an integer variable say ‘
`n`

’ which holds the last term of the series. - Create Scanner class object.
- Prompt the user to enter a number as value of
`n`

. - Declare an integer variable say ‘
`sum`

‘and initialize it with 0. - Declare an integer variable
`i`

and initialize it with 1. - Continue a while loop
`till i<=n/2`

- Inside while loop we will first check the index of
`i`

, if`i`

is even then we will subtract`i*2`

from`sum`

Else we will add`i*2`

in sum.

- Print the result.

**Program:**

import java.util.*; public class Main { public static void main(String args[]) { //creating object of Scanner class Scanner s = new Scanner(System.in); //Taking input of number of elements in the series System.out.println("Enter the value of last number 'n' "); int n = s.nextInt(); // while loop to print the series int sum = 0; int i = 1; while(i <= n/2) { if (i % 2 == 0) sum -= i * 2; else sum += i * 2; i++; } System.out.println("Sum of the series is " + sum); } }

Output: Enter the value of last number 'n' 40 Sum of the series is -20

### Method-3: Java Program to Find the Sum of Series 2-4+6-8+…-/+N By Using User Defined Method

**Approach:**

- Declare an integer variable say ‘
`n`

’ which holds the last term of the series. - Create Scanner class object.
- Prompt the user to enter a number as value of
`n`

. - Then call a user defined method say
`m1()`

and pass`n`

as parameter. - Inside method declare an integer variable say ‘
`sum`

‘and initialize it with 0. - Use a for loop
`from i =1 to i<=n/2`

- Inside for loop we will first check the index of
`i`

, if`i`

is even then we will subtract`i*2`

from`sum`

Else we will add`i*2`

in sum.

- Print the result.

**Program:**

import java.util.*; public class Main { public static void main(String[] args) { // creating object of scanner class Scanner s = new Scanner(System.in); //Taking input of number of elements in the series System.out.println("Enter the value of last exponent 'n' "); int n = s.nextInt(); // calling m1 method to print the series m1(n); } public static void m1(int n) { //for loop to print the series int sum = 0; for (int i = 1; i <= n/2; i++) { if (i % 2 == 0) sum -= i * 2; else sum += i * 2; } System.out.println("Sum of the series is " + sum); } }

Output: Enter the value of last exponent 'n' 10 Sum of the series is 6

Beginners and experienced programmers can rely on these Best Java Programs Examples and code various basic and complex logics in the Java programming language with ease.

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