Niu Ke classic example 3, character shift

Put the uppercase letters of a string after the string, the relative positions of each character remain unchanged, and no additional space can be applied.

Enter    AkleBiCeilD

output    kleieilABCD

import java.util.Scanner;

public class S1 {
	
	public static void main(String args[]){
		Scanner m=new Scanner(System.in);
		while (m.hasNext()) {					
			String str=m.nextLine();
			StringBuilder upperStr = new StringBuilder();  
		    StringBuilder lowerStr = new StringBuilder();
		    StringBuilder allstr=new StringBuilder();
			int i=0;
			while(i < str.length()){  
	            char chr = str.charAt(i);  
	            if(Character.isUpperCase(chr)){  
	                upperStr.append(chr);  
	            }else if(Character.isLowerCase(chr)){  
	                lowerStr.append(chr);  
	            }  
	            i++;  
	        }  
			allstr.append(lowerStr);	
			allstr.append(upperStr)	;
			
			System.out.println(allstr);
		}
		
	}
}