Java中的StringBuilder性能测试

Java中的StringBuilder性能测试

在看KMP算法时,想要简单的统计一下执行时间和性能。

得出的结论是： java的String的indexOf方法性能最好，其次是KMP算法，其次是传统的BF算法，当然，对比有点牵强，SUN的算法也使用Java来实现、用的看着不像是KMP，还需要详细研究一下。

测试代码如下所示：

package com.test.test.kmp;

import java.util.Random;

public class KMPTest {

public static void main(String[] args) {

test();

}

//

public static void test() {

//

int allLen = 8000000;

int subLen = 11;

int charLen = 4;

String cl = buildString(charLen);

int times = 50;

//

testMatch(allLen, subLen, cl, times);

}

public static void testMatch(int allLen, int subLen, String cl, int times){

int allBF = 0;

int allString = 0;

int allKMP = 0;

int allGC = 0;

int allbuild = 0;

int alltoArray = 0;

long start = System.currentTimeMillis();

System.out.println("--------------------------");

for (int i = 0; i < times; i++) {

// 1. 构造字符串的损耗

long buildStart = System.currentTimeMillis();

String sub = buildString(subLen, cl);

String all = buildString(allLen, sub) +sub;

long buildEnd = System.currentTimeMillis();

allbuild += (buildEnd - buildStart);

// 2. toCharArray的损耗

long toArrayStart = System.currentTimeMillis();

char[] allArray =http:// all.toCharArray();

char[] subArray = sub.toCharArray();

long toArrayEnd = System.currentTimeMillis();

alltoArray += (toArrayEnd - toArrayStart);

//

long startBF = System.currentTimeMillis();

int indexBF = bfIndexOf(all, sub);

long endBF = System.currentTimeMillis();

//

long timeoutBF = endBF - startBF;

allBF += timeoutBF;

System.gc();

allGC += (System.currentTimeMillis() - endBF);

//

long startString = System.currentTimeMillis();

int indexString = stringIndexOf(all, sub);

long endString = System.currentTimeMillis();

//

long timeoutString = endString - startString;

allString += timeoutString;

System.gc();

allGC += (System.currentTimeMillis() - endString);

//

long startKMP = System.currentTimeMillis();

//int indexKMP = kmpIndexOf(all, sub);

int indexKMP = KMP_Index(allArray, subArray);

long endKMP = System.currentTimeMillis();

//

long timeoutKMP = endKMP - startKMP;

allKMP += timeoutKMP;

System.gc();

allGC += (System.currentTimeMillis() - endKMP);

//

//System.out.println("all="+all.substring(0,100)+" ......");

//System.out.println("sub="+sub);

//

//System.out.println("indexBF="+indexBF+";耗时: "+timeoutBF+"ms");

//System.out.println("indexString="+indexString+";耗时: "+timeoutString+"ms");

if(indexBF == indexString && indexKMP == indexString){

//System.out.println("!!!!对比相等。");

} else {

throw new RuntimeException("对比出错.");

}

//

if(i % 20 == 10){

System.out.println(i+"次bfIndexOf= "+allBF+"ms");

System.out.println(i+"次stringIndexOf= "+allString+"ms");

System.out.println(i+"次KMPIndexOf= "+allKMP+"ms");

System.out.println(i+"次allbuild= "+allbuild+"ms");

System.out.println(i+"次alltoArray= "+alltoArray+"ms");

System.out.println(i+"*3次,GC= "+allGC+"ms");

long end = System.currentTimeMillis();

long allTime = end-start;

long lossTime = allTime - (allBF+allString+allKMP+allGC);

System.out.println(i+"次,所有总计耗时: "+(allTime)+"ms; 损耗:" + lossTime +"ms; 损耗比: " +((0.0+lossTime)/allTime * 100)+"%");

System.out.println("--------------------------");

}

}

//

System.out.println(times+"次bfIndexOf;总计耗时: "+allBF+"ms");

System.out.println(times+"次stringIndexOf;总计耗时: "+allString+"ms");

System.out.println(times+"次KMPIndexOf;总计耗时: "+allKMP+"ms");

System.out.println(times+"次allbuild= "+allbuild+"ms");

System.out.println(times+"次alltoArray= "+alltoArray+"ms");

System.out.println(times+"*3次,GC;总计耗时: "+allGC+"ms");

long end = System.currentTimeMillis();

long allTime = end-start;

long lossTime = allTime - (allBF+allString+allKMP+allGC);

System.out.println(times+"次,所有总计耗时: "+(allTime)+"ms; 损耗:" + lossTime +"ms; 损耗比: " +((0.0+lossTime)/allTime * 100)+"%");

System.out.println("--------------------------");

}

//

// 构建字符

public static String buildString(int len){

return buildString(len, null);

}

public static String buildString(int len, String sub){

//

final int TYPE_NUMBER = 0;

final int TYPE_LOWERCASE = 1;

final int TYPE_UPPERCASE = 2;

//

long seed = System.nanoTime();

Random random = new Random(seed);

//

//

StringBuilder builder = new StringBuilder();

for (int i = 0; i < len; i++) {

//

int type = random.nextInt(3);// 0-2

int cvalue = 0;

if(TYPE_NUMBER == type){

cvalue = '0' + random.nextInt(10);// 0~(n-1)

} else if(TYPE_LOWERCASE == type){

cvalue = 'a' + random.nextInt(26);// 0~(n-1)

} else if(TYPE_UPPERCASE == type){

cvalue = 'A' + random.nextInt(26);// 0~(n-1)

} else {

throw new RuntimeException(Random.class.getName()+"#newxtInt(int);Wrong!");

}

//

//cvalue = 'A' + random.nextInt(26);// 0~(n-1)

//

char c = (char)cvalue;

if(null != sub && sub.length() > 1){

int index = random.nextInt(sub.length());

c = sub.charAt(index);

}

//String s = String.valueOf(c);

builder.append(c);

//

}

//

return builder.toString();

}

/**

* Java自带的方法,内部实现了

* @param all

* @param sub

* @return

*/

public static int stringIndexOf(String all, String sub){

// 防御式编程

if(null == all || null== sub){

return -1;

}

// 调用Java的String方法

return all.indexOf(sub);

}

/**

* BF算法

* @param all

* @param sub

* @return

*/

public static int bfIndexOf(String all, String sub){

// 防御式编程

if(null == all || null== sub){

return -1;

}

//

int lenAll = all.length();

int lenSub = sub.length();

int i = 0;

while (i < lenAll) {

// 从i下标开始对比

int j = 0;

while (j < lenSub) {

//

char all_i = all.charAt(i);

char sub_j = sub.charAt(j);

if(all_i == sub_j){

// 相等则继续对比下一个字符

i++;

j++; // 这个增长很重要

} else {

// 否则跳出内层循环

break;

}

}

// 如果 j 增长到和 lenSub相等,则匹配成功

if(lenSub == j){

return i - lenSub;

} else {

i = 1+i - j; // 回溯 i

}

}

//

return -1;

}

/**

* KMP 算法

* @param all

* @param sub

* @return

*/

public static int kmpIndexOf(String all, String sub){

//

char[] allArray = all.toCharArray();

char[] subArray = sub.toCharArray();

//

return KMP_Index(allArray, subArray);

}

/**

* 获得字符串的next函数值

*

* @param t

* 字符串

* @return next函数值

*/

public static int[] next(char[] t) {

int[] next = new int[t.length];

next[0] = -1;

int i = 0;

int j = -1;

while (i < t.length - 1) {

if (j == -1 || t[i] == t[j]) {

i++;

j++;

if (t[i] != t[j]) {

next[i] = j;

} else {

next[i] = next[j];

}

} else {

j = next[j];

}

}

return next;

}

/**

* KMP匹配字符串

*

* @param allArray

* 主串

* @param subArray

* 模式串

* @return 若匹配成功，返回下标，否则返回-1

*/

public static int KMP_Index(char[] allArray, char[] subArray) {

int[] next = next(subArray);

int i = 0;

int j = 0;

while (i <= allArray.length - 1 && j <= subArray.length - 1) {

if (j == -1 || allArray[i] == subArray[j]) {

i++;

j++;

} else {

j = next[j];

}

}

if (j < subArray.length) {

return -1;

} else

return i - subArray.length; // 返回模式串在主串中的头下标

}

}

测试的一个结果如下所示：

--------------------------

10次bfIndexOf= 94ms

10次stringIndexOf= 56ms

10次KMPIndexOf= 76ms

10次allbuild= 5870ms

10次alltoArray= 137ms

10*3次,GC= 155ms

10次,所有总计耗时: 6388ms; 损耗:6007ms; 损耗比: 94.03569192235442%

--------------------------

30次bfIndexOf= 365ms

30次stringIndexOf= 222ms

30次KMPIndexOf= 295ms

30次allbuild= 16452ms

30次alltoArray= 395ms

30*3次,GC= 452ms

30次,所有总计耗时: 18184ms; 损耗:16850ms; 损耗比: 92.66388033435987%

--------------------------

50次bfIndexOf;总计耗时: 550ms

50次stringIndexOf;总计耗时: 335ms

50次KMwYryyJHPIndexOf;总计耗时: 450ms

50次allbuild= 26501ms

50次alltoArray= 637ms

50*3次,GC;总计耗时: 734ms

50次,所有总计耗时: 29211ms; 损耗:27142ms; 损耗比: 92.91705179555647%

--------------------------

从中可以看出来，使用StringBuilder构造字符串，800万*50次append大约消耗了26秒。换算下来每秒钟是1600万次。。。

看来是需要写一个专门计时的函数，本来Junit是有自己的统计的，但是样本不太好做。

如此看来，数据的准备，也就是测试用例的选取很关键,可能需要先生成并写入到文本文件中。

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