java和javascript中实现substr_count

tory320

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Java JavaScript PHP Eclipse J#

php中的方法真是不少，今天觉得自己实现一下substr_count。
由于今天比较忙，就没自己想实现方法，google了一下，发现了3种，其中的两个方法真是巧妙，我要是自己实现估计只能想到第一，也就是看起来最笨的那个。不过考虑一下性能，笨方法居然是最快的

package util;

import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;

/**
 * This class is used to test the performance of the method for getting how
 *** 
 **/
public class CountSubString {

	public static void main(String[] args) throws Exception{
		CountSubString count = new CountSubString();
		
		String source = "";
		String sub = "tan";
		StringBuffer sb = new StringBuffer();
		
		for (int i = 0; i < 1000000; i++) {
			sb.append("tan");
			sb.append("tory");
			sb.append("eddie");		
		}
		
        source = sb.toString();
        
        //String newSource = count.replace("tan", "aa", source);
          String newSource = source.replaceAll("t", "aa");
        //System.out.println(newSource);
        
        //File outPut = new File("d:/eclipse3.4/outputfile.dat");
        
        BufferedWriter bw = new BufferedWriter(new FileWriter("d:/eclipse3.4/outputfile.dat"));
        bw.write(newSource);
        bw.flush();
        bw.close();
		long timeStart = System.currentTimeMillis();
		int subStringCount = count.getCountByChar(source, sub);
		long timeEnd = System.currentTimeMillis();
		
		System.out.println("Sub String occurs times is: " + subStringCount);
		System.out.println("The method getCountByChar consumes " + (timeEnd - timeStart));
		
		timeStart = System.currentTimeMillis();
	    subStringCount = count.getCountByReplace(source, sub);
	    timeEnd = System.currentTimeMillis();
		System.out.println("Sub String occurs times is: " + subStringCount);
		System.out.println("The method getCountByReplace consumes " + (timeEnd - timeStart));
		
		timeStart = System.currentTimeMillis();
		subStringCount = count.getCountBySplit(source, sub);
		timeEnd = System.currentTimeMillis();
		System.out.println("Sub String occurs times is: " + subStringCount);
		System.out.println("The method getCountBySplit consume " + (timeEnd - timeStart));
		
		
	}

	public int getCountByChar(String source, String sub) {
		int count = 0;
		int pos = source.indexOf(sub.charAt(0));

		do {
			next: if (pos > -1) {
				// boolean isEqual = true;
				for (int j = 1; j < sub.length(); j++) {
					if (source.charAt(pos + j) != sub.charAt(j)) {
						// isEqual = false;
						break next;
					}
				}

				// if (isEqual)
				count++;

			}

			pos = source.indexOf(sub.charAt(0), pos + 1);

		} while (pos != -1);

		return count;
	}

	public int getCountBySplit(String source, String sub) {
		int count = 0;

		String[] sourceArray = source.split(sub);
		count = sourceArray.length - 1;

		return count;
	}
	
	public int getCountByReplace(String source, String sub) {
		int count  = 0;
		
		count = (source.length() - source.replaceAll(sub, "").length()) / sub.length();
		
		return count;
	}
	
	
}

java的实现有了，javascript就很好办了

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
<title>Sub String Count</title>
<head>
<script type="text/javascript">
//get the count of the sub string occurs in the source
function getCountByChar(source, sub) {
	var count = 0;
    var pos = source.indexOf(sub.charAt(0));
   
    do {
	//next:
      if (pos > -1) {
			  var isEqual = true;
		   for (var i = 1; i < sub.length; i++) {
			if (source.charAt(pos + i) != sub.charAt(i)) {
			    isEqual = false;
				break;
			}
					
		  }
		if (isEqual) 
	    count++;
	  }
	  pos = source.indexOf(sub.charAt(0), pos + 1);
   } while(pos > -1)
   
   return count;
}

function getCountBySplit(source, sub) {
	var count = 0;
	count = source.split(sub).length - 1;
	return count;
}

function getCountByReplace(source, sub) {
	var count = 0;
	var replacSource = source.replace(/tan/g, "");
	count = (source.length - replacSource.length) / (sub.length) ;
	return count;
}

function capSentence() {
    var str = document.getElementById("content").value;
	var result = document.getElementById("resultDiv");
	result.innerHTML = str + escape("Programming PHP啊");
	document.getElementById("resultChar").value = getCountByChar(str, "tan") + "getCountByChar";
	document.getElementById("resultSplit").value = getCountBySplit(str, "tan") + "getCountBySplit";
	document.getElementById("resultReplace").value = getCountByReplace(str, "tan") + "getCountByReplace" ;
}
</script>

<style type="text/css">
input.cap {text-transform: capitalize;}
</style>
</head>

<body>

<input id="content" class="cap" type="text" />
<input type="button" onclick="capSentence();" value="Capitaliz" />
<div id="resultDiv"></div>
<input id="resultChar"  type="text" />
<input id="resultSplit"  type="text" />
<input id="resultReplace"  type="text" />
</body>
</html>

调试过程中发现了几个问题，
第一， java的当字符串很长的时候replaceAll方法会抛outofmemory异常，字串匹配的越多，需要的内存就越大。给eclipse加上如下参数可以增加虚拟机的内存-Xms32m -Xmx256m
第二，也就是昨天发现的javascript的replace方法，只有以/tan/g形式才能替换所有的字串，但目前只找到这种hardcode的方法，不知道怎么通过变量实现

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