累加算法的疑惑 数据类型不对么？? 400 报错

累加算法的疑惑 数据类型不对么？? 400 报错

public static void main(String[] args) {
		//9223372036854000000
		int n = 100000;
		long startTime = System.currentTimeMillis();
		long sum1 = ((1+n)*n)/2;
		long Timeused = System.currentTimeMillis() - startTime;
		System.out.println("sum1="+sum1+" Timeused:"+Timeused);
		
		long sum2 =0;
		startTime = System.currentTimeMillis();
		for (int i = 1; i <= n; i++) {
			sum2=sum2+i;
		}
		Timeused = System.currentTimeMillis() - startTime;
		System.out.println("sum2="+sum2+" Timeused:"+Timeused);
	}

输出是

sum1=705082704 Timeused:0
sum2=5000050000 Timeused:1

环境64BIT OS JDK 1.6最新