Core Java, often referred to as “Java SE” (Standard Edition), is the fundamental and essential part of the Java programming language. It forms the core foundation on which all other Java technologies and platforms are built. Core Java encompasses the basic features, libraries, and concepts of the Java language that are essential for general-purpose programming. Here are some key aspects of Core Java:

1. Basic Syntax: Core Java covers the fundamental syntax and structure of the Java programming language, including data types, variables, operators, and control flow statements (e.g., if, switch, loops).

2. Object-Oriented Programming (OOP): Java is an object-oriented language, and Core Java teaches the principles of OOP, such as classes, objects, inheritance, polymorphism, encapsulation, and abstraction.

3. Standard Libraries: Core Java includes a comprehensive set of standard libraries (Java API) for tasks like I/O operations, networking, data structures, and utility functions. These libraries are part of the java.* and javax.* packages.

4. Exception Handling: Core Java introduces exception handling mechanisms for graceful error handling. It covers try-catch blocks, checked and unchecked exceptions, and the throw and throws keywords.

5. Multi-Threading: Java’s support for multi-threading is an essential part of Core Java. It covers the creation and management of threads, synchronization, thread safety, and concurrency control.

6. File I/O: Core Java teaches file input and output operations, allowing you to read from and write to files using classes like File, FileInputStream, FileOutputStream, and others.

7. Collections Framework: It introduces the Java Collections Framework, including interfaces like List, Set, and Map, along with concrete implementations like ArrayList, HashSet, and HashMap.

8. Networking: Core Java covers basic network programming using classes like Socket and ServerSocket for building client-server applications and network communication.

9. Swing and AWT: Core Java introduces graphical user interface (GUI) programming with the Abstract Window Toolkit (AWT) and Swing libraries. You can create desktop applications with graphical interfaces.

10. Applets: Core Java includes a brief introduction to Java applets, which are small Java applications that can be embedded in web pages. However, applets have become less common with the advent of web technologies like JavaScript and HTML5.

11. JAR Files: Core Java covers the creation and usage of Java Archive (JAR) files for packaging and distributing Java applications and libraries.

12. Command-Line Tools: It teaches how to compile and run Java programs using command-line tools such as javac (Java Compiler) and java (Java Virtual Machine).

13. Annotations: Core Java introduces annotations, which are used for metadata and code generation. Annotations are widely used in modern Java frameworks.

Core Java serves as a strong foundation for various other Java technologies, including Java EE (Enterprise Edition) for building enterprise-level applications, JavaFX for creating rich client applications, and Android development for mobile app development.