String与StringBuilder的空间与时间效率测试分析

package com.yqq.app12;


public class TestApp {
    public static void main(String[] args) {
        String str = "";
        long num1 = Runtime.getRuntime().freeMemory();//获取系统剩余内存空间
        long time1 = System.currentTimeMillis();//获取系统当前时间
        for (int i = 0; i < 10000; i++) {
            str = str+i;//此处产生了10000个对象
        }
        long num2 = Runtime.getRuntime().freeMemory();
        long time2 = System.currentTimeMillis();
        System.out.println("String占用多少内存："+(num1-num2));
        System.out.println("String占用多少时间："+(time2-time1));
        StringBuilder sb = new StringBuilder();
        long num3 = Runtime.getRuntime().freeMemory();
        long time3 = System.currentTimeMillis();
        for (int i = 0; i < 10000; i++) {
            sb.append(i);
        }
        long num4 = Runtime.getRuntime().freeMemory();
        long time4 = System.currentTimeMillis();
        System.out.println("StringBuilder占用多少内存："+(num3-num4));
        System.out.println("StringBuilder占用多少时间："+(time4-time3));
    }
}

由此可见。。。。。。。。。。