Java Day 7

What is a Java Package? 📦

In Java, a package is a mechanism for organizing related classes and interfaces into a single group, much like using a folder to organize files in Windows. By grouping classes this way, you can manage your code more effectively.

The package keyword is used to declare a package, and it must be the very first statement in your Java source file.

Example:

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Java

package sum;

public class Addition {
    // Class content goes here
}

## Advantages of Using Packages

Organizing your Java classes into packages provides two main benefits:

• Fast Searching: It becomes easier and faster to locate the classes you need because they are logically grouped. For example, all database-related classes might be in a database package.
• Name Reusability: Packages prevent naming conflicts. You can have two classes with the same name, as long as they are in different packages. For instance, you could have a com.example.Date class and also use the built-in java.util.Date class in the same project without any issues.

## Types of Packages

There are two main types of packages in Java:

1. Predefined (Built-in) Packages

These are packages that are part of the Java API, created by the developers of Java. They provide a rich library of pre-written classes to perform common tasks.

• Examples:
• java.lang: Contains fundamental classes like String and System. It's automatically imported into every Java program.
• java.util: Provides utility classes like Scanner, ArrayList, and Date.
• java.io: Includes classes for input and output operations.
• java.sql: Used for database connectivity (JDBC).
• java.net: Provides classes for network programming.

2. User-defined (Custom) Packages

These are packages created by you, the programmer, to organize your own project’s classes.

• Examples:
• basic
• com.tcs.online_shopping

## Compiling a Class with a Package

When you have a .java file that includes a package statement, you need to use a specific command to compile it correctly so that the folder structure is created.

• Command: javac -d . FileName.java
• javac: The Java compiler.
• -d: An option that specifies the destination directory for the generated .class files.
• .: Represents the current directory. This tells the compiler to create the package folder structure within the current directory.

Example: If you have a file named Addition.java with the statement package sum; at the top, you would compile it using:

Bash

javac -d . Addition.java

This command will compile the Addition.java file and then automatically create a folder named sum. Finally, it will place the compiled Addition.class file inside the sum folder.