CODEWITHSUNDEEP
javaprivateinner-classesfinaloverriding
PareekSandeep
PareekSandeep

Reputation: 430

inner class have access to private final methods in base class but why?

Why creators of java allowed this situation? I am sure there must be some reason for it. My below code allows Lion to mischievously run as fast as Cheetah. 

public class animal {
    class carnivores {
       private final void runAsFastAsCheetah() {
           System.out.println("Ran as fast as Cheetah");
        }
    }
    public class Lion extends carnivores {
       public void runAsFastAsLion() {
           System.out.println("Ran as fast as Lion.");
           super.runAsFastAsCheetah();
        }
    }
    public static void main(String[] args) {
        animal animal = new animal();
        Lion lion = animal.new Lion();
        //lion.runAsFastAsCheetah(); //Not allowed but//
        lion.runAsFastAsLion();
    }
}

EDIT: For those taking Lion and cheetah seriously, I have modified code.

public class foo {
    class A {
        private final void myMethod() {
            System.out.println("in private final myMethod()");
        }
    }
    public class B extends A {
        public void myMethod() {
            System.out.println("in B's myMethod()");
            super.myMethod();
        }
    }
    public static void main(String[] args) {
        foo foo = new foo();
        B b = foo.new B();
        b.myMethod();
    }
}

Upvotes: 0

Views: 163

Answers (2)

Peter Lawrey
Peter Lawrey

Reputation: 533520

All classes with the same outer class can access private members of any other class of the same outer. This features was added when nested classes were added. IMHO this was because these members are compiled together and it makes nested classes more useful.

Note: The JVM doesn't support this feature, and thus the compiler add accessor methods which appear the the stack traces like access$100. These are added by the compiler to allow access to private members between classes.

Access modifiers only check one level. If A can access B and B and access C, then A can access anything B lets it access which could be C.

The reason this is don't is to avoid making private meaningless. If a private member could only be accessed by class which could access it, it would mean it could only be called by a main in the same class. This would make it useless in any other class.

Upvotes: 2

Jamie Cockburn
Jamie Cockburn

Reputation: 7555

From the Java Language Specification:

A member (class, interface, field, or method) of a reference type, or a constructor of a class type, is accessible only if the type is accessible and the member or constructor is declared to permit access:

  • ...
  • Otherwise, the member or constructor is declared private, and access is permitted if and only if it occurs within the body of the top level class (§7.6) that encloses the declaration of the member or constructor.

In other words, within a top-level class, private and protected no longer apply.

As for the why, well if you think of everything in a class being accessible by that class, then that includes everything inside any inner classes too!

Upvotes: 1

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