Using binary, take a non-empty subset of strings

public class BinaryAlgorithm {
	
	
	/**
	 * In the linux system, 1, 2, and 4 represent execute, write, and read respectively
	 * actually in binary
	 * 0001
	 * 0010
	 * 0100
	 * It can be seen that the sum of any non-empty subset is different
	 * Use this feature to calculate a subset of a set
	 */
	public List<String> getStrSubstringSet(String str){
		List<String> result = new ArrayList<String>();
		
		char[] chars = str.toCharArray();
		int length = chars.length;//string length
		int countStr = 2<<length - 1;//How many non-empty subsets are there
		
		for (int i = 1; i <= countStr; i++) {
			String binaryString = Integer.toBinaryString(i);//Convert the number of subsets to binary
			
			int zeroCount = length - binaryString.length();
			for (int j = 0; j < zeroCount; j++) binaryString = "0"+binaryString;//Complete the length to be the same as the character length
			
			char[] binaryStr = binaryString.toCharArray();//Binary string
			StringBuilder sb = new StringBuilder();
			for (int j = 0; j < binaryStr.length; j++) {
				if(binaryStr[j]=='1') sb.append(str.charAt(j));//If it is 1 here, record it
			}
			result.add(sb.toString());
		}
		return result;
	}
	
	
	public static void main(String[] args) {
		BinaryAlgorithm ba = new BinaryAlgorithm();
		System.out.println(ba.getStrSubstringSet("abcd"));
	}
}