nr: #1 dodano: 2017-01-02 19:01
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:
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.
 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.
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
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
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.