Java Technology – Beginner Explanation
Java is both:
- a programming language, and
- a platform.
This means Java is used to write programs and also provides an environment to run those programs.
Java Software Distributions
Java software is available in different forms, depending on your need.
JRE (Java Runtime Environment)
- JRE is required to run Java programs
- It includes:
- JVM (Java Virtual Machine)
- Core Java libraries
- JRE is mainly used by end users
- If you only want to run a Java application, JRE is enough
JDK (Java Development Kit)
- JDK is required to write and compile Java programs
- It includes:
- JRE
- Java Compiler
- Other development tools
- JDK is mainly used by Java developers
In simple words:
- JRE → Run Java programs
- JDK → Write + Compile + Run Java programs
Java Distributions from Oracle
Oracle provides Java in the following editions:
1. JDK (Java Development Kit)
- Used by Java developers
- Includes:
- Complete JRE
- Tools for developing, debugging, and monitoring Java applications
2. Server JRE (Server Java Runtime Environment)
- Used for server-side applications
- Includes:
- JVM
- Server-related monitoring tools
- Does not include:
- Browser plug-in
- Auto-update
- Installer
- Mainly used on servers, not on personal computers
3. JRE (Java Runtime Environment)
- Used by end users
- Contains everything required to run Java applications
- Suitable for systems where development is not required
Important Java Concepts
- Bytecode
Java programs are compiled into bytecode, not directly into machine code. - JVM (Java Virtual Machine)
JVM executes the bytecode and makes Java platform-independent
(Write Once, Run Anywhere)