Java中測試StringBuilder、StringBuffer、String在字符串拼接上的性能

應一個大量字符串拼接的任務

測試一下StringBuilder、StringBuffer、String在操作字符串拼接時候的性能

性能上理論是StringBuilder  >  StringBuffer  >  String

測試方法：

創建一個StirngTest類含有靜態常量字符串是26個字母，以及一個循環輪數

在測試時采用循環來操作字符串的拼接，計算操作時間並輸出：

package com.test.xlc;

import java.util.Random;

public class StringTest {
    
    static final String strFinal = "abcdefghijklmnopqrstovwxyz";
    static final int forInt = 100;
    
    static void StringBuilderTest() {
        
        Random rand = new Random(47);
        StringBuilder strB = new StringBuilder();
        long start = System.currentTimeMillis();
        for(int i = 0; i < forInt; ++i) {
            int randInt = rand.nextInt(23);
            strB.append(strFinal.substring(randInt, randInt + 4));
        }
        long end = System.currentTimeMillis();
//        System.out.println(strB.toString());
        System.out.println("StringBuilderTest:" + (end - start));
    }
    
    static void StringBufferTest() {
        Random rand = new Random(47);
        StringBuffer strB = new StringBuffer();
        long start = System.currentTimeMillis();
        for(int i = 0; i < forInt; ++i) {
            int randInt = rand.nextInt(23);
            strB.append(strFinal.substring(randInt, randInt + 4));
        }
        long end = System.currentTimeMillis();
//        System.out.println(strB.toString());
        System.out.println("StringBufferTest:" + (end - start));
    }
    
    static void StringOnly() {
        Random rand = new Random(47);
        String str = "";
        long start = System.currentTimeMillis();
        for(int i = 0; i < forInt; ++i) {
            int randInt = rand.nextInt(23);
            str += strFinal.substring(randInt, randInt + 4);
        }
        long end = System.currentTimeMillis();
//        System.out.println(str);
        System.out.println("String:" + (end - start));
    }
    
    
    public static void main(String...args) {
        StringBuilderTest();
        StringBufferTest();
        StringOnly();
        
    }
}

 

測試循環次數：

100

StringBuilderTest:0
StringBufferTest:0
String:0

 

1000

StringBuilderTest:1
StringBufferTest:0
String:7

 

10000

StringBuilderTest:2
StringBufferTest:2
String:217

 

100000

StringBuilderTest:12
StringBufferTest:10
String:17136

 

1000000

StringBuilderTest:55
StringBufferTest:53
我提前終止了

 

之后我又測試了拼接長串，本實驗結果顯示在拼接字符串的效率上：

StringBuffer  >    StringBuilder  >  String