Java – Why did Java make package access default

access-modifiersencapsulationjavalanguage-specificationsunit testing

I'm asking this question because I believe they did it for a very good reason and that most people do not use it properly, well from my experience in industry so far anyway.
But if my theory is true then I'm not sure why they included the private access modifier…?

I believe that if default access is properly used it provides enhanced testability whilst maintaining encapsulation. And it also renders the private access modifier redundant.

The default access modifier can be used to provide the same affect by using a unique package for methods that need to be hidden from the rest of the world, and it does this without compromising testability, as packages in a test folder, with the same are able to access all the default methods declared in a source folder.

I believe this is why Java uses package access as 'default'. But I'm not sure why they also included private access, I'm sure there is a valid use case…

Best Answer

I guess they had a good idea of what an average programmer would do. And by average programmer I mean one who is not really good at programming, but gets the job anyway because there are not enough good ones and they are expensive.

If they made "public" access the default one, most programmers would never bother to use anything else. The result would be a lot of spaghetti code everywhere. (Because if you are technically allowed to call anything from anywhere, why ever bother to encapsulate some logic within a method?)

Making "private" the default access would only be slightly better. Most beginning programmers would simply invent (and share on their blogs) a rule of thumb that "you need to write 'public' everywhere", and then they would complain why Java is so bad that it forces them to write "public" everywhere. And they would also produce a lot of spaghetti code.

The package access is something that allows programmers to use their sloppy programming techniques while writing code within one package, but then they have to reconsider it when making more packages. It is a compromise between good business practices and the ugly reality. Like: write some spaghetti code, if you insist, but please leave the ugly mess within the package; at least create some nicer interfaces among the packages.

Probably there are other reasons, too, but I wouldn't underestimate this one.

Related Solutions

Java – Why Is There No ‘Subclasses-Only’ Access Modifier in Java?

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

I assume that was a judgment call that the extra complexity wasn't worth the cost.

Every language feature has a cost: in teaching it to new programmers; in documentation; in implementing it in the compiler, JVM, and dev tools; in reasoning about program correctness; in constraining future language evolution; and more. Language features interact with each other, potentially with N² interactions.

What percent of Java programmers have read through the Java language spec and VM spec? I bet it's a small percentage, which argues for an even simpler language for the sake of understandability and engineering products that we can depend on

The benefit of the private protected feature was small since the package is the main unit of modularity.

Java – Is Default Package included in the Package Level Access

The default package is the package without a name, all classes without a package declaration at the top of the file fall into it.

It is subject to all normal rules of packages except that you can't reference classes of it from a class inside a package.

For example I have 2 java files:

public class A{
    public static void foo(){System.out.println("fooCalled");}
}

and

package com.example;

public class B{
    public static void main(String[] arg){
        A.foo();//won't compile
    }

}

Then B (or in the qualified form com.example.B) can never call the foo of A without reflection magic.

If you ever start making larger programs then you should put all your code in packages. It allows you to segregate your code in a way that makes sense.

The accepted practice is to name you package after a domain the program is part of like com.example

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Related Solutions

Java – Why Is There No ‘Subclasses-Only’ Access Modifier in Java?

Java – Is Default Package included in the Package Level Access

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