用Java编程计算: 一根木棒折三段，能构成三角形的概率

面试时遇到的一道恶心的笔试题目：一根木棒折为三段，这三段可以构成一个三角形的概率？

public class Triangle {
??? /**
??? ?* 一根绳子任意切两刀组成三角形的概率
??? ?*
??? ?* @param args
??? ?*/
??? private static long x = -1L; // first side of the triangle
??? private static long y = -1L; // second side of the triangle
??? private static long z = -1L; // thirdly side of the triangle
??? private static long length = 1000L; // length of the triangle
??? private static long loop = 10000000L; // how many time to run?
??? private static long num = 0; // how many valid triangles?

??? public static void main(String[] args) {
??? ??? method();

??? }

??? private static void method() {
??? ??? for (long i = 0L; i < loop; i++) {
??? ??? ??? // to keep valid time for loop
??? ??? ??? while (true) {
??? ??? ??? ??? x = (long) (Math.random() * length);
??? ??? ??? ??? y = (long) (Math.random() * length);
??? ??? ??? ??? z = length - x - y;
??? ??? ??? ??? if (z > 0L && x > 0L && y > 0L) {
??? ??? ??? ??? ??? break;
??? ??? ??? ??? }
??? ??? ??? }
//??? ??? ??? System.out.println(x + " " + y + " " + z);
??? ??? ??? if (x + y > z && x + z > y && z + y > x) {
//??? ??? ??? ??? System.out.println(x + " " + y + " " + z);
??? ??? ??? ??? num++;
??? ??? ??? }
??? ??? }
??? ??? double percent = ((num * 1.0) / loop) * 100; // "long" convert to "double"
??? ??? System.out.println(percent + "%");

??? }

}