package com.atguigu.test10; /* * Runtime:JVM运行时环境 * Runtime是一个单例的实现 */ public class TestTime { public static void main(String[] args) { // testStringBuilder(); testStringBuffer(); // testString(); } public static void testString(){ long start = System.currentTimeMillis(); String s = new String("0"); s += i; } long end = System.currentTimeMillis(); System.out.println("String拼接+用时:"+(end-start));//444 long memory = Runtime.getRuntime().totalMemory() - Runtime.getRuntime().freeMemory(); System.out.println("String拼接+memory占用内存: " + memory);//53185144字节 } public static void testStringBuilder(){ long start = System.currentTimeMillis(); StringBuilder s = new StringBuilder("0"); for(int i=1;i<=10000;i++){ s.append(i); } long end = System.currentTimeMillis(); System.out.println("StringBuilder拼接+用时:"+(end-start));//4 long memory = Runtime.getRuntime().totalMemory() - Runtime.getRuntime().freeMemory(); System.out.println("StringBuilder拼接+memory占用内存: " + memory);//1950488 } public static void testStringBuffer(){ long start = System.currentTimeMillis(); StringBuffer s = new StringBuffer("0"); for(int i=1;i<=10000;i++){ s.append(i); } long end = System.currentTimeMillis(); System.out.println("StringBuffer拼接+用时:"+(end-start));//7 long memory = Runtime.getRuntime().totalMemory() - Runtime.getRuntime().freeMemory(); System.out.println("StringBuffer拼接+memory占用内存: " + memory);//1950488 } }