java - access of protected field from other class -

for below code, can access protected fields of seatplan class , change value classroom class, looks not secure data.

is normal? isn't protected fields can accessed subclass only? otherwise need change them private field?

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let's have abstract class protected fields:

public abstract class seatplan {     protected int rownum;     protected int columnnum;      public abstract void method(); } 

then has child classes:

public class aseatplan extends seatplan {     public aseatplan(){            // constructor         this.rownum= 10;          this.columnnum = 7;     }     // omitted code }  public class bseatplan extends seatplan {     public bseatplan(){            // constructor         this.rownum= 7;         this.columnnum = 15;     }     // omitted code } 

a class room contains private field of seatplan object:

public class room {     private seatplan seatplan;      public room(seatplan seatplan){       // constructor         this.seatplan = seatplan;     }      public seatplan getseatplan(){     // getter method         return seatplan;     }      //omitted code }  public class classroom {     public seatplan dosomething(room room){         seatplan seats = room.getseatplan();         seats.rownum = 99999;     <--------------- accidentally change value ------      //omitted code     } 

i think confusing c# java.

in c#, protected stuff can accessed subclasses. in java, protected stuff can accessed in same package or in subclass.

that's why can change value of seat plan classroom.

is not secure?

imo, is. don't think should change row , column number of seat plan.

how make it's secure?

you should redesign seat plan class. here's rough idea:

public final class seatplan {     private seatplan(int rownum, int colnum) {         this.rownum = rownum;         this.colnum = colnum;     }      private int rownum;     private int colnum;      //you should add getters rownum , colnum here     //but i'm lazy did not      public static final seatplan plan_a = new seatplan(10, 7);     public static final seatplan plan_b = new seatplan(7, 15); }