Package In Java

In Java, a package is a way to structure code and organize classes, interfaces, and sub-packages into a single namespace, making it achievable to manage and maintain large-scale Java apps.

It helps in avoiding naming conflicts and provides a way to encapsulate related classes and interfaces.

Here are some key points about packages in Java:

Namespace Management:

Packages provide a way to manage namespaces in Java.

They allow us to group related classes and interfaces under a common namespace, which helps in avoiding naming conflicts.

Access Control:

Packages also play a role in access control. Classes and interfaces within the same package have access to each other's members (fields, methods, constructors) with default or package-private access level.

This means that they can be accessed within the same package but not from outside.

Import Statements:

When we want to use a class or interface from another package in your Java code, you typically use import statements.

These import statements inform the compiler about the classes or interfaces that your code depends on and where to find them.

Standard Packages:

Java comes with a large number of standard packages that provide various functionalities.

For example, "java.lang" contains fundamental classes like "String" and "Object", "java.util" contains utility classes like "ArrayList" and "HashMap", and so on.

Creating Packages:

To create your package in Java, we simply declare it at the beginning of your Java source file using the `package` keyword followed by the package name.

This declaration must be the first non-comment statement in the file.

Syntax:

// import package in current file
package com.example.yourproject;

public class YourClass {
    // Class implementation
}

Create a file named "orderhistory.java"

Example:

package com.orders;

public class OrderHistory {
    public static void fetchUserOrderHistory() {
        System.out.println("Fetch Order Placed by Specific User");
    }
    
}

Example:

package com.orders;

public class User {
    public static void main(String[] args) {
        OrderHistory.fetchUserOrderHistory();
    }
}

Create a file named "user.java"

Example:

javac com/orders/*.java

// after complied successfully run below command
java com.orders.User

Save "user.java" and "order history.java" inside a directory named `com/orders`.

Compile the above code using command:

Package Structure:

Packages in Java typically follow a hierarchical naming convention, similar to directory paths in file systems.

For example, "com.example.yourproject" is a package name where "com" is the top-level domain, "example" is the domain name, and "yourproject" is a subpackage.

Note:

Packages are a crucial part of Java programming as they help in organizing and managing code in larger projects.

They contribute to code reusability, maintainability, and readability by providing a structured way to organize classes and interfaces.

<-- Encapsulation

Access Modifier -->