Why Does the "Protected" Modifier in Java Allow Access to Other Classes in Same Package

Why does the protected modifier in Java allow access to other classes in same package?

This design is based on the idea that the package is the appropriate unit, maintained and released by one internally consistent team; inheritance relationships have much less to do with who's maintaining and releasing what when.

Why protected can be access in same Package without inheritance in java?

Why? Because that's how the Java programming language was designed. There's not much more to it.

Something that is protected is accessible from

• the class itself,
• classes in the same package (doesn't matter if they are subclasses or not),
• subclasses (doesn't matter if they are in the same package or not).

This is different from C++, but Java is not C++, so it doesn't necessarily work in the same way.

In Java, why can a protected member be accessed from outside the class within the same package?

In his book, Herbert Schildt says in page 172 (3rd paragraph) that "protected applies only when inheritance is involved.".

There's an argument that that statement is correct, although I'd say it's quite misleading. Let's look at the access chart from the access control tutorial:

Modifier    Class  Package  Subclass  World
public        Y       Y        Y       Y
protected     Y       Y        Y       N
no modifier   Y       Y        N       N
private       Y       N        N       N

Note that no modifier grants both class and package access to the member, and does not grant access to subclasses or the world. protected only changes one of those things: It makes the member available to subclasses. So in that sense, he's correct: It only applies when inheritance is involved; without inheritance, it's the same as having no modifier.

But I find it quite misleading, for the very reason that inspired your question: It seems to imply that there won't be package access. The only way the statement makes sense is if you already know that no modifier grants package access.

For clarity: protected means a member is available to any class in the package and to code in subclasses. Doing this makes it possible for a library to have fields and methods you only access from code that's part of the library* (sort of, see below) or code that helps implement something in the library (for instance, if you're subclassing from one of the library classes). There's no particular "why" other than that's how the language was designed.

If it is so, then I find no difference between the public and protected specifiers in this situation.

In this situation, no. There's obviously quite a large difference, though, when you consider code that isn't in the same package and isn't in a derived class of a package member: That code has no access to protected members.

This is covered in JLS§6.6.1:

...if the member or constructor is declared protected, then access is permitted only when one of the following is true:

• Access to the member or constructor occurs from within the package containing the class in which the protected member or constructor is declared.

• Access is correct as described in §6.6.2.

(note the first bullet) and JLS§6.6.2:

A protected member or constructor of an object may be accessed from outside the package in which it is declared only by code that is responsible for the implementation of that object.

("code that is responsible for the implementation of that object" — e.g., code in a subclass.)

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* Re my "sort of, see below" on "Doing this makes it possible for a library to have fields and methods you only access from code that's part of the library..." That's not really true, because except for the restricted packages (java.lang, for instance), you can happily write your own class saying it's in the library's package, and then use the package level fields and methods of the library's classes. Java's package concept is not a field/method security mechanism.

What is the difference between public, protected, package-private and private in Java?

The official tutorial may be of some use to you.

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