You can control whether the world outside your class can access its members. This is known as visibility of the member.
In other words, you can expose only certain members to public, that is the world outside your class, while keep other members private or protected. Thus, you can control the access of your members. The visibility modifiers are a form of encapsulation in Java.
You will use visibility modifiers very often. There are four visibility levels in Java.
* Package
* Public
* Private
* Protected
The visibility modifiers determine which members of your class are visible to other classes. With access control, you can tell the compiler how your class can be used by other classes. You can use only one visibility modifier at a time.
You can use the private modifier to hide a class member from all the other classes. In other words, a private member is accessible only within its class.
Some members of a class are useful only within the class. There is no point in such members being accessed from other classes. In such cases, you should always use the private modifier.
In fact, fields are usually marked as private. You will learn more about this later in this chapter.
A member declared without any visibility modifier is accessible to all the classes in the same package. We will learn more about this visibility when we learn about packages.
The protected member is accessible to the following two groups. * Subclasses of a class * Other classes in the same package
You will learn more about subclasses and packages later in this book.
In some cases, you want your class members to be completely visible to the outside world. In other words, any class can access the member.
You can use the public modifier to make a member completely visible to all the classes.
In fact, you have already used the public modifier from the beginning of this book.
The main() method of an application has to be public. Otherwise, it cannot
not be invoked by the Java Virtual Machine (JVM).