关于String，StringBuffer,StringBuilder的区别

String 字符串常量

StringBuffer 字符串变量（线程安全）

StringBuilder 字符串变量（非线程安全）

效率:StringBuilder>StringBuffer>String

          注:如果是单线程序的话，优先考虑StringBuilder,如果是多线程的话，则考虑StringBuffer

案例如下:

package com.seven.exercise.StringTest;

     import org.junit.Test;

     public class StringBufferWithStringBuilder {

     public void testString() {
        long start = System.currentTimeMillis();
        String str = null;
        for (int i = 0; i < 20000; i++) {
            str = str + i + ",";
        }
        System.out.println(System.currentTimeMillis() - start);
    }

    public void testStringBuffer() {
        long start = System.currentTimeMillis();

        StringBuffer sbuf = new StringBuffer();
        for (int i = 0; i < 20000; i++) {
            sbuf.append(i + ",");
        }
        System.out.println(System.currentTimeMillis() - start);
    }

    public void testStringBulider() {
        long start = System.currentTimeMillis();

        StringBuilder builder = new StringBuilder();
        for (int i = 0; i < 20000; i++) {
            builder.append(i + ",");
        }
        System.out.println(System.currentTimeMillis() - start);
    }

    @Test
    public void test(){
        testString();
        testStringBuffer();
        testStringBulider();
    }
    
}

运行结果如下:

1217

9

6