package test_demon;

public class try1 {
    String str1 =new String("123");
   

    public void change(String str)
    {
        str = "ok";
    }

public static void main(String[] args) {
        try1 ex= new try1();
        ex.change(ex.str1);
        System.out.print(ex.str1);
    }
}

import java.util.Scanner;
public class Change {
        public String str="123";
        public void change(String str)
        {
            this.str=str;
        }

    public static void main(String[] args) {
           Change change1=new Change();   
           Scanner s=new Scanner(System.in);
           String str=s.next();
           change1.change(str);
            System.out.print(change1.str);
        }
    }
希望对你有帮助！！！