将字符串中出现的第n个字符置换

package com.zyx.cn.baidu_test;

/**

 字符串"asd as da s" 将出现的第三个a置换成b；变为"asd as db s"

 * @author yltd

 *

 */

public class Test {

public static void main(String[] args) {

String s ="asd as da s";

int number =0;

String str="" ;

for (int i = 0; i < s.length(); i++) {

String newChar = s.substring(i,i+1);

if("a".equals(newChar)||newChar=="a"){

number++;

if(number==3){

str= s.substring(0, i);

str =str+"b";

str = str + s.substring(i+1, s.length());

System.out.println(str);

}

}

}

}

}