Printing all possible subsets of a list

import java.io.*;
import java.util.*;
class subsets
{
    static String list[];
    public static void process(int n)
    {
        int i,j,k;
        String s="";
        displaySubset(s);
        for(i=0;i<n;i++)
        {
            for(j=0;j<n-i;j++)
            {
                k=j+i;
                for(int m=j;m<=k;m++)
                {
                    s=s+m;
                }
                displaySubset(s);
                s="";
            }
        }
    }
    public static void displaySubset(String s)
    {
        String set="";
        for(int i=0;i<s.length();i++)
        {
            String m=""+s.charAt(i);
            int num=Integer.parseInt(m);
            if(i==s.length()-1)
                set=set+list[num];
            else
                set=set+list[num]+",";
        }
        set="{"+set+"}";
        System.out.println(set);
    }
    public static void main()
    {
        Scanner sc=new Scanner(System.in);
        System.out.println("Input ur list");
        String slist=sc.nextLine();
        int len=slist.length();
        slist=slist.substring(1,len-1);
        StringTokenizer st=new StringTokenizer(slist,",");
        int n=st.countTokens();
        list=new String[n];
        for(int i=0;i<n;i++)
        {
            list[i]=st.nextToken();
        }
        process(n);
    }
}

A java solution based on Petar Minchev solution -

public static List<List<Integer>> getAllSubsets(List<Integer> input) {
    int allMasks = 1 << input.size();
    List<List<Integer>> output = new ArrayList<List<Integer>>();
    for(int i=0;i<allMasks;i++) {
        List<Integer> sub = new ArrayList<Integer>();
        for(int j=0;j<input.size();j++) {
            if((i & (1 << j)) > 0) {
                sub.add(input.get(j));
            }
        }
        output.add(sub);
    }

    return output;
}

Use bitmasks:

int allMasks = (1 << N);
for (int i = 1; i < allMasks; i++)
{
    for (int j = 0; j < N; j++)
        if ((i & (1 << j)) > 0) //The j-th element is used
           System.out.print((j + 1) + " ");

    System.out.println();
}

Here are all bitmasks:

1 = 001 = {1}
2 = 010 = {2}
3 = 011 = {1, 2}
4 = 100 = {3}
5 = 101 = {1, 3}
6 = 110 = {2, 3}
7 = 111 = {1, 2, 3}

You know in binary the first bit is the rightmost.