java - How to make object referencing to the same thing? -

public class number {     private int j;     public number(){         j = 3;     }      public number(int m){         j = m;     }      public void setnum(int n){         j = n;     }      public int getnum(){         return j;         }      } 

/// (different file, same directory)

    public class user {         private number jim;          public user(){                 this.jim = new number();             }              public static void main(string []args){                 user keith = new user();                 user justin = new user();                 ??????????????????????????             }      } 

i want keith.jim = justin.jim , justin.jim = keith.jim. such if keith.jim.setnum(34), both keith , justin's jim.j 34. how that? idea implement in bigger piece of code.

also, user.java , number.java must exist. context cannot changed,i can add new methods cannot alter context in number (e.g put j in user instead of number). each user must have number object every users referencing well.

others have suggested creating 1 user object. alternative have 2 user objects, same reference value of jim field:

user keith = new user(); user justin = new user(); justin.jim = keith.jim; 

this useful if have other fields keith , justin need different, change in object value of jim field refers must seen both.

both of these valid options, depending on requirements.

a few points, however:

• this means original value of justin.jim because pointless; consider adding user constructor taking number reference initial value of field, allowing write:

  user justin = new user(keith.jim); 

• shared mutable state can become tricky reason about, particularly in face of multiple threads
• as noted in comments, should rename number class isn't in java.lang (or java.util etc, if possible).
• you should follow java naming conventions methods, using camelcase instead of pascalcase - i'd call them getvalue , setvalue, personally.