认识String、StringBuilder、StringBuffer的区别

String:字符串常量，非线程安全

StringBuilder:字符串变量，非线程安全

StringBuffer:字符串变量，线程安全

下面自己写的测试效率的代码

package com.jaws.string;

import com.jaws.util.TimeUtil;

public class KnowStringClient {
public static void main(String[] args) {
String name = "I am String A";
String age = ",i am twenty senven year old" ;
String job = ",my job is Java Coder.";
String fors = ".";
Long before = 0L , after=0L;
//Test for Spring
before = TimeUtil.getNowLong();
String strTest = name+age+job;
for (int i = 0; i < 5000; i++) {
strTest+=fors;
}
//System.out.println(strTest);
after = TimeUtil.getNowLong();
System.out.println("String: "+TimeUtil.getDiffLong(before, after));
//Test for SpringBuilder
before = TimeUtil.getNowLong();
StringBuilder builderTest = new StringBuilder();
builderTest.append(name);
builderTest.append(age);
builderTest.append(job);
for (int i = 0; i < 5000; i++) {
builderTest.append(fors);
}
System.out.println(builderTest.toString());
after = TimeUtil.getNowLong();
System.out.println("StringBuilder: "+TimeUtil.getDiffLong(before, after));
//Test for SpringBuffer
before = TimeUtil.getNowLong();
StringBuffer bufferTest = new StringBuffer();
bufferTest.append(name);
bufferTest.append(age);
bufferTest.append(job);
for (int i = 0; i < 5000; i++) {
bufferTest.append(fors);
}
System.out.println(bufferTest.toString());
after = TimeUtil.getNowLong();
System.out.println("StringBuffer: "+TimeUtil.getDiffLong(before, after));
}
}

执行结果：

I am String A,i am twenty senven year old,my job is Java Coder........................

String: 31

I am String A,i am twenty senven year old,my job is Java Coder.......................

StringBuilder: 0

I am String A,i am twenty senven year old,my job is Java Coder..........................

StringBuffer: 15

从执行结果看在单线程测试效率情况，StringBuilder>StringBuffer>String，用String拼接花了31毫秒，StringBuilder执行太快没能显示出差值，

StringBuffer花了15毫秒，测试多次StringBuffer也有多次没能显示出差值，三个对象的执行效率都是非常快，所以我觉得在日常开发中重点注

意的是线程安全的问题，如果一个字符串可能被多个线程修改需使用StringBuffer对象。

以上是小弟的见解，如果有对的地方，望指出，乐意接受批评