import java.util.ArrayList;

public class Subset {
	/**Given array*/
	String[] list;
	/**Number of elements in a given array*/
	int count;
	/**List to store subsets*/
	ArrayList<String> arrayList = new ArrayList<>();

	/**
	 *constructor
	 * @param list
	 */
	public Subset(String[] list) {
		this.list = list;
		count = list.length;
		arrayList = new ArrayList<>();
		//Find a subset
		for(int i=0;i<count;i++) {
			execute(i, "");
		}
	}

	/**
	 *Find a subset using a recall call based on arguments
	 * @param num
	 * @param str
	 */
	public void execute(int num, String str) {
		if(num < count) {
			if(str == "") {
				str = list[num];
			}
			arrayList.add(str);
			for(int i=num+1;i<count;i++) {
				execute(i, str + ", " + list[i]);
			}
		}
	}
}

public class Main {
	public static void main(String args[]) {
		String[] list = {"A", "B", "C", "D"};

		Subset subset = new Subset(list);

		for(String str:subset.arrayList) {
			System.out.println(str);
		}
	}

}

A
A, B
A, B, C
A, B, C, D
A, B, D
A, C
A, C, D
A, D
B
B, C
B, C, D
B, D
C
C, D
D

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