자바 문자열 뒤짚기

public class Start02 {
    public String reverseStr(String str){    
        int num = str.length();
        int[] temp = new int[num]; 
        String tempStr = "";
        for(int i = num-1; i >= 0; i--){              
            temp[i] = (int)str.charAt(i);             
            tempStr += (char)temp[i];
        }         
        return str =tempStr;
    }
    
    public static void main(String[] args) {
        Start02 rs = new Start02();
        System.out.println( rs.reverseStr("Zbcdefg") );
    }
}

import java.util.Arrays;
import java.util.Collections;
 
public class Start02 {
    public String reverseStr(String str){    
        String[] array = str.split("");
        Arrays.sort(array);
        Collections.reverse(Arrays.asList(array));
        return String.join("", array);
    }
    
    public static void main(String[] args) {
        Start02 rs = new Start02();
        System.out.println( rs.reverseStr("Zbcdefg") );
    }
}