Does Java have a "private protected" access modifier?

Question

I have seen some references refer to a access modifier in Java called private protected (both words together):

private protected someMethod() {

}

One of the pages I found referring to this is here. My school lesson also referred to this access modifier (and said it exists). Using it, however, results in an error in the Java language.

I tried with both variables and methods and I'm pretty sure it doesn't exist, but I want an explanation of what happened. Was it considered, then rejected? Or did it get removed in a newer version of Java?

Edit: I am not looking for info about the protected keyword.

Answer 1

Removal of the access modifier

Java did originally have the private protected modifier, but it was removed in JDK 1.0.2 (the first stable version, the Java 1.0 we know today). A few tutorials regarding JDK 1.0.2 (here and here) say the following:

Note: The 1.0 release of the Java language supported five access levels: the four listed above plus private protected. The private protected access level is not supported in versions of Java higher than 1.0; you should no longer be using it in your Java programs.

Another answer on SoftwareEngineering.SE states:

Java originally had such a modifier. It was written private protected but removed in Java 1.0.

Now take a look at the Java Version History:

JDK 1.0

The first version was released on January 23, 1996 and called Oak. The first stable version, JDK 1.0.2, is called Java 1.

From this, we can conclude the tutorials regarding version 1.0.2 refer to the very first version, JDK 1.0, where the language was called Oak, but the one from SoftwareEngineering.SE refers to the first stable version, JDK 1.0.2 called Java 1.0, where it was removed.

Now if you try to search for it in the Java 1.0 documentation, you won't find it, because as mentioned earlier, it was removed in JDK 1.0.2, otherwise known as Java 1.0. This is proven again when you look at the "Last Modified" times for the link you posted. The link you posted was last modified in February of 1996. Java 1.0/JDK 1.0.2, when private protected was removed, was released after February of 1996, and according to the specification, August of 1996.

Reason for removal

Some sources also explain the reason for private protected, such as this one. To quote:

What was private protected?

Early on, the Java language allowed for certain combinations of modifiers, one of which was private protected. The meaning of private protected was to limit visibility strictly to subclasses (and remove package access). This was later deemed somewhat inconsistent and overly complex and is no longer supported.[5]

[5] The meaning of the protected modifier changed in the Beta2 release of Java, and the private protected combination appeared at the same time. They patched some potential security holes, but confused many people.

And the SoftwareEngineering.SE also supports this, by saying that it wasn't worth the inconsistencies and extra complexity, so it was removed early on.

Interpretation

My interpretation of all this is that maybe, back in the Oak days, both were allowed to coexist (hence the combination). Since protected's meaning had changed¹, there may have been a need for allowing private and protected at the same time. The introduction became too complex and wasn't worth it, and was thus dropped in the end. By the time Java 1.0/JDK 1.0.2 rolled around, it had been dropped and thus cannot be found in the documentation.

---

¹In the Oak Language Specification, Section 4.10, Access to Variables and Methods, it is noted that the default modifier was protected:

By default all variables and methods in a class are protected.

This is quite different from what we have today, the default package access. This may have paved the way for the need of private protected, because private was too restrictive and protected was too lenient.

Answer 2

There are confusing/unclear stories:

One, from the Princeton source you put, and also from MIT archives, states that:

Note: The 1.0 release of the Java language supported five access levels: the four listed above plus private protected. The private protected access level is not supported in versions of Java higher than 1.0; you should no longer be using it in your Java programs.

But this feature is not specified on any official documentation for Java 1.0 here or here.

My guess is that this feature didn't make it to the official 1.0 version, since the official language specification is from August 1996 and Princeton source was last modified on February 1996.

PS: shame on Oracle for removing the archives for older versions.

Answer 3

As the link you provided in your question suggests private protected was used on an element/member of a class, when you want your subclass to be able access the element but keep it hidden from other classes in its package.

Java if compared to C++ has an extra concept of encapsulating elements - and that is a Package. One should also understand what is accessible within or outside a package in Java when it comes to these access-specifiers like private, public & protected.

Please note that I have explained why it was used. Not in current version of course

Answer 4

No, you can't use both private a protected together. Your tutorial is strange. What you do have is so called package private or in ot6 references package protected access. This is default access that is enabled when no acc6 qualifier is written explicitly.

Answer 5

Private scope is withing the existing class. Wherein Protected can be access within package and class extended by classes in other packages.

Seamlessly if you want your variable/methods to be access outside the package you need to define as protected/public otherwise private or some other access specifiers.

Protected methods are usually accessible from outside package and within sub-classes, i.e a class has to extend respective class to avail protected defined methods.

Private methods/variables have scope within the class.They cant be accessible outside the class.

Hence you can't define Private Protected at a same time!