Java实现解析IP地址的方法，给出一串数字，生成正确的IP地址

import java.util.ArrayList;
import java.util.List;
public class TestIP {
//Java实现解析IP地址的方法，给出一串数字，通过方法生成正确的IP地址
public List<String> restoreIpAddresses(String s) {
ArrayList<ArrayList<String>> result = new ArrayList<ArrayList<String>>();
ArrayList<String> t = new ArrayList<String>();
dfs(result, s, 0, t);
ArrayList<String> finalResult = new ArrayList<String>();
for(ArrayList<String> l: result){
StringBuilder sb = new StringBuilder();
for(String str: l){
sb.append(str+".");
}
sb.setLength(sb.length() - 1);
finalResult.add(sb.toString());
}
return finalResult;
}
public void dfs(ArrayList<ArrayList<String>> result, String s, int start, ArrayList<String> t){
//if already get 4 numbers, but s is not consumed, return
if(t.size()>=4 && start!=s.length())
return;
//make sure t's size + remaining string's length >=4
if((t.size()+s.length()-start+1)<4)
return;
//t's size is 4 and no remaining part that is not consumed.
if(t.size()==4 && start==s.length()){
ArrayList<String> temp = new ArrayList<String>(t);
result.add(temp);
return;
}
for(int i=1; i<=3; i++){
//make sure the index is within the boundary
if(start+i>s.length())
break;
String sub = s.substring(start, start+i);
//handle case like 001. i.e., if length > 1 and first char is 0, ignore the case.
if(i>1 && s.charAt(start)=='0'){
break;
}
//make sure each number <= 255
if(Integer.valueOf(sub)>255)
break;
t.add(sub);
dfs(result, s, start+i, t);
t.remove(t.size()-1);
}
}
}