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probably try to use factorial method to generate all possible strings from a given string. eg, string "abc" can be written as {abc,acb,bac,bca,cab,cba}..So, we got 3! number of words...this technique can be used along with rearranging the string

public class PermutationOfStrings {

/**
*
* @param arr
*/
static void printArray(char arr[]) {
System.out.print("\n");
for (int i = 0; i < arr.length; i++) {
System.out.print(arr[i]);
}
}

/**
*
* @param i
* @param j
* @param arr
*/
static void permute(int i, int j, char arr[]) {
if (i == j) {
printArray(arr);
} else {
permute(i + 1, j, arr);

for (int z = i; z < j; z++) {
char temp = arr[i];
arr[i] = arr[i + 1];
arr[i + 1] = temp;
permute(i + 1, j, arr);

}

}
}

/**
*
* @param args
*/
public static void main(String[] args) {

permute(0, 3, new char[] { 'a', 'b', 'c', 'd' });
}

}

String ConcatenateStr(String str) {
return str +str;
}
String reverseString(String str){
   return str.reverse();//reverse the string using any algo.
}

printPermutOfString(String str){
int sze= str/2;
  for(int i=0;i<sze; i++){
    int j=i;
    Sysout(str.subStr(j,sze); //extracts substr from index j to length sze;
}
}
PSV main(String args[]){
  String input = "abc";
  String concStr = ConcatenateStr(input);  //abcabc
  printPermutOfString(concStr);//abc,bca,cab --output
String revStr = reverseStr(concStr);cbacba
printPermutOfString(revStr )//cba,bac,acb --ouput

}

public class StringCombinations {

	public static void main (String[] args) {
		StringCombinations s = new StringCombinations();
		s.printStringCombinations("abcd".toCharArray(), 0);
	}

	private void printStringCombinations(char[] s, int level) {

		if (level == s.length) {
			System.out.println(s);
			return;
		}

		for (int i = level; i < s.length; i++) {
			swap(s, i, level);
			printStringCombinations(s, level + 1);
			swap(s, i, level);
		}
	}

	private void swap (char[] s, int position1, int position2) {
		char temp = s[position1];
		s[position1] = s[position2];
		s[position2] = temp;
	}
}

public static void stringCombinations(String prefix, String str){

if(str.length() == 0){
System.out.println(prefix);
return;
}

for(int i = 0 ; i < str.length() ;i++){

stringCombinations(prefix + str.charAt(i), str.substring(0, i) + str.substring(i+1, str.length()));

}
}

Here I am assuming we can convert string to a array of characters and then proceed.

Length of a substring can be between (1 n), for any given length m, find all the combination of a binary array which contain m 1s and rest are all 0. and then print only those value of original array for which value in binay array is 1.

for example: input: 'abc', for length 1, binary array can be [100] [010] [001] == > print ==>a,b,c
for length 2, binary array [110][101][011] ==> ab, ac, bc

Here is working code

public class StringSubSet {
	public static void PrintCombiOfGivenLength(char[] B, int[] Helper, int start, int remain){
		if(remain == 0) {
			System.out.print("[");
			for (int i=0;i<Helper.length;i++){
				if(Helper[i] == 1)System.out.print(B[i]+",");
			}
			System.out.println("]");
			return;
		}
		else{
			for(int i=start;i<B.length;i++){
				Helper[i] = 1;
				PrintCombiOfGivenLength(B,Helper,i+1,remain-1);
				Helper[i] = 0;
			}
		}
	}
	public static void main(String[] args) {
		char[] B = {'a','b','c'};
		int[] Helper = new int[B.length];
		for(int i=1; i<=B.length; i++) {
			PrintCombiOfGivenLength(B,Helper,0,i);
		}
	}
}

We can do the permutation of the Characters.
here is the Java code:

import java.io.*;

public class StringPermutaion {
static StringBuffer result;
static int len=0;
public static void main(String[] args) throws IOException{
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
String input = br.readLine();
len = input.length();
result = new StringBuffer(input);
permute(0);
}
static void permute(int i){
if(i==len)
System.out.println(result);
else{
for(int j=i;j<len;j++)
{
swap(i,j);
permute(i+1);
swap(i,j);
}
}
}
static void swap(int i, int j){
char temp = result.charAt(i);
result.setCharAt(i, result.charAt(j));
result.setCharAt(j, temp);
}
}

how to print like below pattern through java language
B C
A