---

This simple Java Program generates all possible sub String of given string.You can replace string with StringBuilder or StringBuffer where performance is issue.

package com.techy.rajeev;

public class GenStr {

/**
     * @param args
     */
public static void genAllSubStr(String str){
for(int i=0;i<str.length();i++){
for(int j=i;j<str.length();j++){
                System.out.println(str.substring(i, j+1));
            }
        }
    }
public static void main(String[] args) {
        genAllSubStr("abc");
    }

}

Output:

a
ab
abc
b
bc
c