第二阶段15-字符序列陷阱_时间和空间效率测试字符序列陷阱

//效率测试
public class TestString2 {
    public static void main(String[]args){
        /**使用String进行字符串的拼接*/
        String str8 = "";
        long num1 = Runtime.getRuntime().freeMemory();//获得系统剩余内存空间
        long time1 = System.currentTimeMillis();//获得系统当前时间
        for(int i = 0;i<5000;i++){
            str8 = str8 + i;//相当于产生了5000个对象
        }
        long num2 = Runtime.getRuntime().freeMemory();
        long time2 = System.currentTimeMillis();
        System.out.println("Strong占用内存："+(num1-num2));
        System.out.println("String占用时间："+(time2-time1));
        /**使用StringBuilder进行字符串拼接*/
        StringBuilder sb1 = new StringBuilder("");
        long num3 = Runtime.getRuntime().freeMemory();
        long time3 = System.currentTimeMillis();
        for(int i = 0;i<5000;i++){
            sb1.append(i);
        }
        long nume4 = Runtime.getRuntime().freeMemory();
        long time4 = System.currentTimeMillis();
        System.out.println("StringBuilder占用内存："+(num3-nume4));
        System.out.println("StringBuilder占用时间："+(time4-time3));
    }
}