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I am learning Java recently, and I came across the notion of package-private classes, which is the default if we don't specify anything. But then I realized:
I seldom see the use of package-private class. Is there a reason for this, e.g., it has serious drawbacks, it is redundant, or simply I am not reading enough? Are there strong arguments for/against its usage?
If it is really not useful in most cases, why would it be the default?
In what situation should we use package-private in the real world? I.e., when would it become irreplaceable?
In other words, what are the major pros and cons of the default package-private modifier?
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In Summary private keyword in java allows most restrictive access to variables and methods and offer strongest form of Encapsulation. private members are not accessible outside the class and private method can not be overridden.
package-private (often just called package) means that other members of the same package have access to the item. package-private is the default access modifier and does not have a keyword, because package is used to specify the package for a class or interface.
When we don't use any keyword explicitly, Java will set a default access to a given class, method or property. The default access modifier is also called package-private, which means that all members are visible within the same package but aren't accessible from other packages: package com.
The private modifier specifies that the member can only be accessed in its own class. 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.
The short answer is - it's a slightly wider form of private.
I'll assume that you're familiar with the distinction between public and private, and why it's generally good practice to make methods and variables private if they're going to be used solely internally to the class in question.
Well, as an extension to that - if you're thinking about creating your software in a modular way, you might think about a public interface to your module, which will have multiple classes inside it collaborating between themselves. In this context it makes perfect sense to make methods public if they're going to be called by consumers; private if they're internal to a class; and package private if they're used to call between classes in this module, i.e. it's an implementation detail of your module (as seen by public callers) but spans several classes.
This is seldom used in practice, because the package system turns out to not be so useful for this sort of thing. You'd have to dump all of the classes for a given module into exactly the same package, which for anything non-trivial is going to get a bit unwieldy. So the idea is great - make a method accessible to just a handful of "nearby" classes, as a slightly wider private - but the restrictions on how you define that set of classes means it's rarely used/useful.
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One nice thing about package-private is that you can use it to give access to methods you would otherwise consider private to unit test classes. The downside of course being that other classes in the package could call it when they really shouldn't.
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