java：数列求和

求9+99+999+…+999999999的和

具体代码如下：

package day03;

public class ArraySum {

	public static void main(String[] args) {
		long sum = 9;
		long nine = 9;
		for(long i = 1; i < 10; i++) {
			nine = nine * 10 + 9;
			sum = sum + nine;
		}
		System.out.println("9+99+999+...+9999999999="+sum);

	}

}