Question

i’m working on a method that split a string based on the . delimiter, i have used the Pattern and Matcher classes, and get the start positions of the delimiter and stored them in an array and now i want to split the specified string based on those start positions, my problem is that when i tried the following code, the program goes forever (Infinite loop).

public void cutByRegex(){
     String outPut="";
     int i=0;
     int startIndex[]=new int[3];
     System.out.println("IP--->"+ip);
     Pattern p=Pattern.compile("\\.");

     Matcher m=p.matcher(ip);
     while (m.find()){
        startIndex[i]=m.start();
        i++;
        System.out.println("start: "+m.start());
     }
     System.out.println("StartIndices-->");
     for(int j:startIndex)
          System.out.println(j);
     for(i=0;i<startIndex.length+1;){
        switch(i){
        case 0:
        outPut+=ip.substring(i,startIndex[i]);
        i++;
        case 1:
           outPut+=ip.substring(startIndex[i]-1,startIndex[i]);
           i++;
        case 2:
           outPut+=ip.substring(startIndex[i]-1,startIndex[i]);
           outPut+=ip.substring(startIndex[i],ip.length());
           break;
        }
     System.out.println("group--->"+outPut);
     }    

    }

for example:
the startIndex array contains 3,5,7
i want to substring 127.1.1.254
from 0—>3
from 4—>5
from 6—>7
from 8—>ip.length

Note:i know the built in method split() well, i want to do the job manually
what mistakes i have done??

Answer 1

You have not used increment part in for loop i variable and case block 2

Your code

    for(i=0;i<startIndex.length+1;){

      case 2:
         outPut += ip.substring(startIndex[i] - 1, startIndex[i]);
         outPut += ip.substring(startIndex[i], ip.length());

         break;
    }

change with it  

 for (i = 0; i < startIndex.length + 1;i++) {    
       case 2:
         outPut += ip.substring(startIndex[i] - 1, startIndex[i]);
         outPut += ip.substring(startIndex[i], ip.length());
         i++;
         break;

        }