Friday, February 15, 2013

Java Access Specifiers & Java Package

Java Access Specifiers

The Java access specifiers are,
  • public
  • private
  • protected

You will visit Java access specifiers public, protected, and private  for each method and  member in your class. Each access specifier controls the access for only that particular definition.

One way or another, everything has some kind of access specified for it. In the following sections, you’ll learn all about the various types of access, starting with the default access.

public

When you use the public keyword, it means that the member that declared as public is available to everyone, i.e. member variable or function that is declared as public, can be accessed from anywhere in the application. It can be accessed from different package also.

private

The private keyword means that no one can access that member except that particular class, inside methods of that class. Other classes in the same package cannot access private members. On the other hand, private variable in the method can be accessed from other method or even class if the method that contain private variable is public.

protected

protected methods and fields can only be accessed within the same package to which the methods and fields belongs,, but not from anywhere else. You use the protected access level when it is appropriate      to require method or field access within same package, but not for unrelated classes.

For Example,

public class Square {   // public class
  private double x, y   // private (encapsulated) instance variables

  public setCorner(int x, int y) {  // setting values of private fields
    this.x = x;
    this.y = y;
  }

  public getCorner() {  // setting values of private fields
    return Point(x, y);
  }
}

Java Packages

A package is what you use to get entire library using import keyword, such as,

import java.util.*;

This brings in the entire utility library that’s part of the standard Java distribution. Since, for example, the class ArrayList is in java.util, you can now either specify the full name java.util.ArrayList.

i.e., if you want to import a single class, you can name that class in the import statement like,

import java.util.ArrayList;

package can also created by programmer, to remove ambiguity in the programmer. If programmer wants to arrange classes modules wise, then he can make different packages for each module and can make low ambiguous application. In practical manner, if more than on programmers are working upon an application, then, if same class name given by two programmers that are working upon different module, then it will not conflict each other. So, in this way, packaging is organizing the application.


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