java - What happens when base and derived classes each have variables with the same name -

consider int a variables in these classes:

class foo {     public int = 3;     public void addfive() { += 5; system.out.print("f "); } } class bar extends foo {     public int = 8;     public void addfive() { this.a += 5; system.out.print("b " ); } } public class test {     public static void main(string [] args){         foo f = new bar();         f.addfive();         system.out.println(f.a);     } } 

i understand method addfive() have been overridden in child class, , in class test when base class reference referring child class used call overridden method, child class version of addfive called.

but public instance variable a? happens when both base class , derived class have same variable?

the output of above program

b 3  

how happen?

there 2 distinct public instance variables called a.

• a foo object has foo.a variable.
• a bar object has both foo.a , bar.a variables.

when run this:

    foo f = new bar();     f.addfive();     system.out.println(f.a); 

the addfive method updating bar.a variable, , reading foo.a variable. read bar.a variable, need this:

    system.out.println(((bar) f).a); 

the technical term happening here "hiding". refer jls section 8.3, , section 8.3.3.2 example.

note hiding applies static methods same signature.

however instance methods same signature "overridden" not "hidden", , cannot access version of method overridden outside. (within class overrides method, overridden method can called using super. however, that's situation allowed. reason accessing overridden methods forbidden break data abstraction.)

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the recommended way avoid confusion of (accidental) hiding declare instance variables private , access them via getter , setter methods. there lots of other reasons using getters , setters too.