题目：
字符串之替换字符串中连续出现的指定字符串
给定3个字符串str from to已知from字符串无重复字符，把str中所有from的子串全都替换成to字符串，连续出现from只需要换成一个to就可。
例如：
str="123adc" from = "adc" to ="4567" 返回1234567
str="123" from = "adc" to ="4567" 返回123
str="123adcabc" from = "adc" to ="X" 返回123X
实现代码：
package com.chenyu.string.cn;
public class RaplaceString {
public static void main(String[] args) {
String target = "000abcabc123abc456abc789abcabc";
String from = "abc";
String to = "def";
String result = replace(target, from ,to);
System.out.print("result:" + result);
}
public static String replace(String target, String from, String to) {
if (target == null || "".equ
