SumOfThreads.java

import java.util.Arrays;
public class SumOfThreads implements Runnable {
	
	static int sum[] = new int[3];
	static int idx = 0;
	int n1, n2;
	
	SumOfThreads(int n1, int n2) {
		this.n1 = n1;
		this.n2 = n2;
	}
	
	public void run() {
		int s1 = ( n1 * ( n1 - 1 ) ) / 2;
		int s2 = ( n2 * ( n2 + 1 ) ) / 2;
		sum[idx] = (s2 - s1);
		idx++;
	}

	public static void main(String[] args) {
		new Thread(new SumOfThreads( 1   , 100)).start();
		new Thread(new SumOfThreads( 101 , 200)).start();
		new Thread(new SumOfThreads( 201 , 300)).start();		
		System.out.println(Arrays.toString(sum));
		int result = 0;
		for(int s : sum) {
			result += s;
		}
		
		System.out.println("Result :: " + result);
	}
}