在Java中，如果您的方法具有未指定的可见性关键字，会发生什么？

Question

I have been working with android for a few years now, not once have I had a teacher or anyone to tell me what to do. This whole time I have wondered to myself this.

When you have a method I generally see...

public void method(){
//Stuff
}

or

private void method(){
//stuff
}

I know that a void is a method with no return value, and that public is the visibility of the method in a way but would it matter if I just used something like this...

void method(){
//stuff
}

Because then the methods visibility would just be default anyway?

I have no idea if I am right or not, is it just good practice to specify "public" or "private" ?

Answer 1

Not specifying anything has a specific meaning:

• public - any class can access this member
• protected - subclasses can access this member (as well as code in the same class or in the same package)
• private - only code in the same class can access this member
• nothing ("default" access) - only code in the same package can access this member

Arguably the last case should have had its own keyword, but we're stuck with it now. Unless you really mean to use default visibility, it's poor form to not specify anything - did you really need package visibility for some reason, or did you just default to package visibility for everything? Best practice is to explicitly use private for non-public members unless you need one of the others.

Answer 2

Java has four levels of visibility: public, protected, (default), private. The meaning of these is as follows:

1. public - makes your methods accessible to any other class.
2. protected - makes your methods accessible to any class in the same package OR any subclass of your class.
3. (default, ie no modifier) - makes your methods accessible only to classes in the same package.
4. private - makes your methods accessible only to the current class.

The same rules apply when specifying the access modifiers on classes, methods and fields.

Answer 3

Java has four levels of visibility: public, protected, (default), private

1. Visible to the package. the default. No modifiers are needed.
2. Visible to the class only (private).
3. Visible to the world (public).
4. Visible to the package and all subclasses (protected).

Default Access Modifier - No keyword:

Default access modifier means we do not explicitly declare an access modifier for a class, field, method etc.

A variable or method declared without any access control modifier is available to any other class in the same package. The default modifier cannot be used for methods, fields in an interface.

Private Access Modifier - private:

Methods, Variables and Constructors that are declared private can only be accessed within the declared class itself.

Private access modifier is the most restrictive access level. Class and interfaces cannot be private.

Variables that are declared private can be accessed outside the class if public getter methods are present in the class.

Using the private modifier is the main way that an object encapsulates itself and hide data from the outside world.

Public Access Modifier - public:

A class, method, constructor, interface etc declared public can be accessed from any other class. Therefore fields, methods, blocks declared inside a public class can be accessed from any class belonging to the Java Universe.

However if the public class we are trying to access is in a different package, then the public class still need to be imported.

Because of class inheritance, all public methods and variables of a class are inherited by its subclasses.

Protected Access Modifier - protected:

Variables, methods and constructors which are declared protected in a superclass can be accessed only by the subclasses in other package or any class within the package of the protected members' class.

The protected access modifier cannot be applied to class and interfaces. Methods, fields can be declared protected, however methods and fields in a interface cannot be declared protected.

Protected access gives the subclass a chance to use the helper method or variable, while preventing a nonrelated class from trying to use it.