Isn't “package private” member access synonymo

问题:

I am a little confused over the term "package private" that some of the documentation uses, along with the usage of "default access." Aren't package private and default access both synonymous with protected?

回答1:

Yes, it's almost the same. The protected modifier specifies that the member can only be accessed within its own package (as with package-private) and, in addition, by a subclass of its class in another package.

回答2:

The "default" access modifier (the one where none of them are explicitly given) is "package-private", which means only things in the same package can access them. However, being in the same package implies nothing about the inheritance relationship between classes -- it's purely a naming convention.

"Protected" means that not only classes in the same package, but also subclasses (regardless of which package those subclasses are in) will be able to access it.

回答3:

The default access for classes is package-private, however the default access for interface members is public.

e.g.

public interface I {
   int A = 1;
// same as
   public static final int A = 1;

   void method();
// same as
   public abstract void method();

   class C { }
// same as
   public static class C { }
}

The default access rules for interfaces are not the same as for classes.

回答4:

Package-private and default access are synonyms. An object can also access protected member of the objects whose classes are in the same package. An object can also access protected member of its superclasses without a condition about their package. As a concrete example :

package ab;

class A {
   protected void foo() {}
   void dd(){}
}

class C {
   void aa(){
       A a = new A();
       a.foo(); //legal
       a.dd();  //legal
   }
}


package sub;

class D extends A{
      void ac(){
         foo(); //legal ..
         dd();  //illegal.. because dd has default access.. 
      }

class E {
    void ee(){
       A a = new A();
       a.foo(); //illegal
       a.dd();  //illegal     
    }

回答5:

'Package private' and default access are the same. In early releases of the compiler around 1.1.2/3, 'package' was an allowed modifier, but ignored, meaning the same as no modifier, i.e. 'package private'. Shortly afterwards there was a short lived fashion for putting /*package*/ (as a comment) in such situations. Similarly at that time you could declare things like synchronized classes, although again there was no actual semantic effect.

Neither of them is the same as 'protected', which extends to derived classes in other packages.

回答6:

From Java Language Spec

• 6.6.5 Example: Default-Access Fields, Methods, and Constructors If none of the access modifiers public, protected, or private are specified, a class member or constructor is accessible throughout the package that contains the declaration of the class in which the class member is declared, but the class member or constructor is not accessible in any other package.

If a public class has a method or constructor with default access, then this method or constructor is not accessible to or inherited by a subclass declared outside this package

回答7:

default and package-private both are same, which means both can be used by any class till they are in same package.

The package-private term, actually, is termed by the meaning of private modifier as private means it is available only in same class and no other classes or subclasses can access it within same package or without.

Hence package-private means same as default.