Difference Between Package and Interface in Java

The key difference between Package and Interface in Java is that Package helps to categorize the classes methodically to access and maintain them easily while Interface helps to implement multiple inheritances and to achieve abstraction.

Java is one of the most popular programming languages. The main advantage of Java is that it supports Object Oriented Programming. This methodology allows modeling the real world objects in software. A class is a blueprint to create an object. Each object contains data or fields to describe the attributes or the properties and methods to describe behaviors. This article discusses two concepts related to OOP in Java  in Java that are Package and Interface.

What is Package in Java?

Java provides a large number of classes. Keeping all the classes in a single folder can be difficult because it is hard to access. This can affect the program manageability. Java uses packages to arrange classes. It is similar to a folder. Java API groups classes into different packages according to the functionality. Therefore, each package contains a related set of classes.

Example of Packages in Java

Few example packages are as follows. The java.io package contains the input, output supporting classes. It includes File, PrintStream, BufferInputStream etc. The java.net package contains the networking related classes. Some examples are URL, Socket, ServerSocket. The java.awt package contains all the classes required to build Graphical User Interfaces. Those are few Java API packages.

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When the programmer wants to use a certain class in the program, he should import that package. If the programmer wants to use the BufferInputStream class in the java.io package, he should write the import statement as follows.

import java.util.BufferInoutStream;

Below statement will import all the classes in the util package.

import java.util.*;

It is also possible to create user defined packages.

package employee;

public class Employee {

}

According to the above example, the employee is the package name. The Employee class is a part of the employee package. This file saves as Employee.java to the employee package.

Furthermore, it is possible to import a public class from one package to another. Refer the following example.

Figure 01: Class A

Figure 02: Class B

Class A is in package 1, and it contains the public method called display. Class B is in package 2, and it contains the main method. Even though they are in separate packages; class B can create an object of class A by importing package1. After importing package 1, class B has access to the data and methods of class A.

Overall, Package in Java helps to organize the project files. This is very useful when developing large system because it allows storing all the files in methodical way.  In addition to that, the Java API packages allow the programmers to use already existing classes.

What is Interface in Java?

Sometimes the programmer might not know the definition of the method. In this situations, the programmer can only declare the method. An abstract method is a method that does not have a definition. It only has the declaration. When there is at least one abstract method, that class becomes an abstract class. Moreover, the abstract class can contain abstract methods as well as non-abstract methods. The programmer cannot create objects out of abstract classes.

When a class extends an abstract class, the new class should define all the abstract method in the abstract class. In other words, assume that abstract class A has an abstract method called display. Class B extends class A. Then class B should define the method display.

Example of Interface in Java

Assume that both A and B are abstract classes. If class C is extending A and B, that class C has to define the abstract methods of both classes. This is multiple inheritance. Java does not support multiple inheritance. To implement it, the programmer should use interfaces. If A and B are interfaces, then class C can implement them. Refer following example.

Figure 03: Interface A

Figure 04: Interface B

The interface A has the display1 abstract method, and interface B has the display2 abstract method.

Figure 05: Class C

Class C implements both A and B interfaces. Therefore, it should define both methods.

Figure 06: Main Method

Now in the main method, it is possible to create an object of C and call both methods. Likewise, interfaces help to implement multiple inheritance in Java.

Other than multiple inheritance, interfaces help to achieve abstraction. It is one major concept in OOP. Abstraction allows to hide the implementation details and show only the functionality to the user. Further, it allows focusing on what the object does instead of how it is done. As an interface consists of abstract methods, it helps to archive abstraction.

What is the Difference Between Package and Interface in Java?

Package is a group of related classes that provide access protection and namespace management. Interface is a reference type similar to class which is a collection of abstract methods. Package helps to categorize the classes methodically to access and maintain them easily. On the other hand, Interface helps to implement multiple inheritances and to achieve abstraction. This is the main difference between Package and Interface in Java. Further, the way to write a package is in lower case letters such as java.util, java.awt. If the name of the interface is Area, then it is written in, interface Area.

Source: differencebetween.com