Finding all combination of a word with length 3 or more

I am trying to implement a program to find all possible combinations of a word with length 3 or more. I have implemented algo with prints all the combinations like for example: for word "digital" it will print digitla diitgla ... and so on. But I also need words with length 3 or more in the output. For example: dig, dit, git, and so on.

Can anyone help me what code shall I include to get the above output?

public class PermTest {

public static void main(String[] args) throws Exception {
    String str = "digital";
    StringBuffer strBuf = new StringBuffer(str);
    doPerm(strBuf,str.length());

}

private static void doPerm(StringBuffer str, int index){

    if(index <= 0)
        System.out.println(str);            
    else { //recursively solve this by placing all other chars at       current first pos
        doPerm(str, index-1);
        int currPos = str.length()-index;
        for (int i = currPos+1; i < str.length(); i++) {//start swapping all other chars with current first char
            swap(str,currPos, i);
            doPerm(str, index-1);
            swap(str,i, currPos);//restore back my string buffer
        }
    } 
}

private  static void swap(StringBuffer str, int pos1, int pos2){
    char t1 = str.charAt(pos1);
    str.setCharAt(pos1, str.charAt(pos2));
    str.setCharAt(pos2, t1);
} 
}