1. Built-in / predefined packages:

Built-in packages are predefined packages provided by Java, which contain a set of commonly used classes and interfaces.
These packages are part of the Java Development Kit (JDK) and are automatically available for use in Java programs.
Examples of standard packages include:

• java.lang: Contains fundamental classes such as String, Object, and basic data types.
• java.util: Provides utility classes for data structures (e.g., lists, maps), date and time manipulation, and input/output operations.
• java.io: Offers classes for handling input and output operations, including file I/O and stream processing.
• java.net: Provides classes for networking operations, such as sockets and URLs.
• java.awt and javax.swing: Used for developing graphical user interfaces (GUI) applications.

2. User-defined Packages:

• User-defined packages are packages created by developers to organize their own classes and interfaces into logical groups.
• These packages are created using the package keyword followed by the package name at the beginning of the source file.
• User-defined packages allow developers to modularize their codebase, improve code organization, and facilitate code reuse across multiple projects.
• By convention, the package name should follow the reverse domain name pattern (e.g., com.example.project) to ensure uniqueness and prevent naming conflicts.

Example of defining a user-defined package:

package com.example.myproject;

public class MyClass {
// Class definition
}