the use of private keyword

Question

I am new to programming. I am learning Java now, there is something I am not really sure, that the use of private. Why programmer set the variable as private then write , ge

Answer 1

I highly recommend the book Effective Java, it contains a lot of useful information about how to write better programs in Java.

Your question is addressed in items 13 and 14 of that book:

• Item 13: Minimize the accessibility of classes and members
• Item 14: In public classes, use accessor methods, not public fields

Answer 2

It depends on who access these public variables. Most likely, only by people inside your company/team. Then it's trivial to refactor them into getters/setters when necessary. I say in this case, it's better to leave the variables public; unless you are forced to follow the java bean convention.

If you are writing a framework or a library intended for the public, then you shouldn't expose variables. It's impossible for you to change them into getters/setters later.

But the 2nd case is more rare than the first; people apply extremely unreasonable assumptions when it come to software engineer, as if they are not writing code, instead they are carving code in stone. And as if the whole world is watching while you code - in reality, nobody will ever read your code except yourself

Answer 3

You shouldn't allow implementations to alter your records directly. Providing getters and setters means that you have exact control over how variables get assigned or what gets returned, etc. The same thing goes for the code in your constructor. What if the setter does something special when you assign a value to size? This won't happen if you assign it directly.

Answer 4

As stated earlier, the reason for making a variable private is to hide it from the outside. But if you make a getter AND a setter then you may as well make the variable itself public. If you find yourself later in a position that you made the wrong choice, then you must refactor your code from using the public variable into using the getter/setter which may not be a problem. But it can be a problem if other code, which you do not control, starts depending on your code. Then such a refactoring will break the other code. If you use getters and setters from the start you will reduce that risk in exchange for a little effort. So it depends on your situation.

Answer 5

This is indeed used to hide the internal implementation. This also helps is providing extra bit of logic on your variables. Say you need to make sure that the value passed for a varable should not be 0/null, you can provide this logic in the set method. Also in the same way you can provide some logic while getting the value, say you have a object variable which is not initialised and you are accessing that object, in this case you cand provide the logic to null check for that object and always return an object.

Answer 6

The most important reason is to hide the internal implementation details of your class. If you prevent programmers from relying on those details, you can safely modify the implementation without worrying that you will break existing code that uses the class.

So by declaring the field private you prevent a user from accessing the variable directly. By providing gettters and setters you control exactly how a user may control the variable.