# Java Program to Display Numbers and Sum of First N Natural Numbers

• Last Updated : 09 Nov, 2020

Print first N natural numbers using an iterative approach i.e. using for loop. For loop has three parameters initialization, testing condition, and increment/decrement.

```Input:     N = 10
Output:    First 10 Numbers = 1, 2, 3, 4, 5, 6, 7, 8, 9, 10
Sum of first 10 Natural Number = 55

Input:     N = 5
Output:    First 5 Numbers = 1, 2, 3, 4, 5
Sum of first 5 Natural Number = 15
```

Approach

1. Start for loop initialization with i = 1.
2. Write testing condition as i <= N.
3. Add increment statement as i++ or i+=1.
4. Initialize a variable sum with 0.
5. Start adding i with the sum at each iteration of for loop and print i.
6. Print sum at the end for loop.

Below is the implementation of above approach

## Java

 `// Java Program to Display Numbers``// from 1 to N Using For Loop and``// sum of First N Natural Number``import` `java.io.*;``class` `GFG {``    ``public` `static` `void` `main(String[] args)``    ``{``        ``int` `N = ``10``;``        ``int` `sum = ``0``;``        ``System.out.print(``"First "` `+ N + ``" Numbers = "``);`` ` `        ``// we initialize the value of the variable i ``        ``// with 1 and increment each time with 1``        ``for` `(``int` `i = ``1``; i <= N; i++) {`` ` `            ``// print the value of the variable as``            ``// long as the code executes``            ``System.out.print(i + ``" "``);``            ``sum += i;``        ``}``        ``System.out.println();``        ``System.out.println(``"Sum of first "` `+ N``                           ``+ ``" Natural Number = "` `+ sum);``    ``}``}`

Output

```First 10 Numbers = 1 2 3 4 5 6 7 8 9 10
Sum of first 10 Natural Number = 55```

Time Complexity: O(n)

Alternate Approach

1. Start for loop initialization with i = 1.
2. Write testing condition as i <= N.
3. Add increment statement as i++ or i+=1.
4. Start Printing i for each iteration.
5. Print sum using first N natural number formula at the end of for loop.

Below is the implementation of the above approach

## Java

 `// Java Program to Display Numbers``// from 1 to N Using For Loop and``// sum of First N Natural Number``import` `java.io.*;`` ` `class` `GFG {``   ` `    ``public` `static` `void` `main(String[] args)``    ``{``        ``int` `N = ``5``;``        ``System.out.print(``"First "` `+ N + ``" Numbers = "``);`` ` `        ``// we initialize the value of the variable i``        ``// with 1 and increment each time with 1``        ``for` `(``int` `i = ``1``; i <= N; i++) {``           ` `            ``// print the value of the variable as``            ``// long as the code executes``            ``System.out.print(i + ``" "``);``        ``}``        ``System.out.println();``        ``System.out.println(``"Sum of first "` `+ N``                           ``+ ``" Natural Number = "` `+ (N*(N+``1``))/``2``);``    ``}``}`

Output

```First 5 Numbers = 1 2 3 4 5
Sum of first 5 Natural Number = 15```

Time Complexity: O(n)

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