Packages In Java

Advantages of Java Package

Types of packages

Built-in Packages

These packages include numerous classes that are a part of the Java API.

• java.lang: includes language-supporting classes (e.g classed which defines primitive data types, math operations). The import of this package is automatic.
• java.io: supports input and output operations with classes.
• java.util: contains utility classes that implement date and time operations as well as linked lists, dictionaries, and other data structures.

User-defined packages

These are the packages the user has defined. First, we create the HELLO directory (name should be same as the name of the package). After that, create the Encapsulation inside the directory with the package names as the first statement.

Example of Packages in Java

 // Java Packages  example  

package HELLO;
class Encapsulation{	 
    private String  EmpName; 
    private int  EmpId;
	public String getEmpName() {
		return EmpName;
	}
	public void setEmpName(String empName) {
		EmpName = empName;
	}
	public int getEmpId() {
		return EmpId;
	}
	public void setEmpId(int i) {
		EmpId = i;
	}   
}
 
class Main {
    public static void main(String[] args){
    	Encapsulation encapsulation = new Encapsulation();
    	encapsulation.setEmpName("Mohan");
    	encapsulation.setEmpId(421658);
        System.out.println("The Name of the Emp is : " +encapsulation.getEmpName()
                                                                        +" & EmpID is : "+encapsulation.getEmpId());
    }
}

The Name of the Emp is : Mohan & EmpID is : 421658 

3 way to access the package from outside the package

Import all classes and interfaces of package (import package.*;)

package tutorial;
public class PackageCheck{
   public void Print(){
      System.out.println("Hello World");
    }
}

package HELLO;
import tutorial.*;
class Main {
    public static void main(String[] args){
    	PackageCheck packageCheck=new PackageCheck();
    	packageCheck.Print();
   }
}

Hello World 

Import package declared class name (import package.classname;)

package tutorial;
public class PackageCheck{
   public void Print(){
      System.out.println("Hello World");
    }
}

package HELLO;
import tutorial.PackageCheck;
class Main {
    public static void main(String[] args){
    	PackageCheck packageCheck=new PackageCheck();
    	packageCheck.Print();
   }
}

Hello World 

When you import a package, all of its classes and interfaces are imported except subpackages. So, you also need to import the subpackage.

Fully qualified name

Only this package's declared classes will be accessible if you use the fully qualified name. There is no longer a need to import. When utilizing a class or interface, however, you must always use the fully qualified name.When two packages belong to the same class, it is commonly used.

package tutorial;
public class PackageCheck{
   public void Print(){
      System.out.println("Hello World");
    }
}

package HELLO;
class Main {
    public static void main(String[] args){
    	tutorial.PackageCheck packageCheck=new tutorial.PackageCheck();
    	packageCheck.Print();
   }
}

Hello World 

Using Static Import

The Java programming language (versions 5 and above) introduced the concept of static import, which enables members (fields and methods) defined in a class as public static to be used in Java code without mentioning the class in which they are defined.

package HELLO;
import static java.lang.System.*;
class Main {
    public static void main(String[] args){
    	 out.println("DockerTpoint");
   }
}

DockerTpoint 

Different ways to load the class files or jar files