Java

Facts

• James Gosling is known as the father of Java.
• Java is an object-oriented, class-based, concurrent, secured and general-purpose computer-programming language.
• Initial Name was oak which was renamed to java
• Main aspects for language
  • Simple
  • Platform independent - JVM & bytecode
  • Object-oriented programming language (except for the primitive types)
  • write once run anywhere - JVM, architecture neutral
  • robust
  • High Performance (JIT)
• More detailed History

Basic Flow

flowchart TD
    src -- compiled to (javac) --> bytecode;
    bytecode -- interpreted by JVM (java) --> execution;

From Java 11 onwards, the compilation and execution step can be combined into a single step. Limitation is that all the source must be written in a single .java file, instead of multiple files.

Java Editions

• Java Standard Edition (Java SE)
  • includes - JDK, JRE, Core Libraries, Java APIs, Languages features etc.
  • fundamental features for security, netowrking and GUI development etc.
• Java Enterprise Edition (Java EE)
  • Extends Java SE, inclues Java Persistentce API, Java Server Pages, Enterprise java bean(ejb) also.
  • adds collection of specification for commercial application
• Java Micro Edition (Java ME) - mobile and embedded devices.
• JavaFX - graphics

Java Feature Releases

• JDK 1.0- Initial release of Java.
• JDK 1.1- Added inner classes, JDBC, and AWT improvements.
• J2SE 1.2 (Java 2)- Introduced Swing, Collections framework.
• J2SE 1.3- Introduced HotSpot JVM, JNDI, and naming conventions.
• J2SE 1.4- Added assert keyword, regular expressions, and Java Web Start.
• J2SE 5.0 (Java 5)- Introduced generics, metadata annotations, and the enhanced for loop.
• Java SE 6 (Java 6)- Added scripting support, monitoring enhancements, and the Java Compiler API.
• Java SE 7 (Java 7)- Introduced try-with-resources, diamond operator, and strings in switch statements.
• Java SE 8 (Java 8)- Landmark release with lambdas, Stream API, java.time package, and Nashorn JavaScript engine.
• Java SE 9 (Java 9)- Introduced the module system (Project Jigsaw).
• Java SE 10 (Java 10)- Focused on developer productivity with local-variable type inference (var).
• Java SE 11 (Java 11) LTS- LTS release with deprecated features removed and stability improvements.
• Java SE 12 (Java 12)- Introduced switch expressions (preview feature) and GC improvements.
• Java SE 13 (Java 13)- Added text blocks and enhancements to switch expressions.
• Java SE 14 (Java 14)- Introduced pattern matching for instanceof, records, and text blocks.
• Java SE 15 (Java 15)- Featured sealed classes, pattern matching for records, and more.
• Java SE 16 (Java 16)- Introduced new language features and Unix domain socket channel.
• Java SE 17 (Java 17) LTS- The latest LTS release, focusing on long-term support and enhancements.
• Java SE 18 (Java 18)- UTF by default, Javadoc code snippets, Switch pattern matching, Vector API, Foreign function & memory API
• Java SE 19 (Java 19)- Foreign function & memory API, Switch pattern matching, Vector API, Structured concurrency
• Java SE 20 (Java 20)- Scoped values
• Java SE 21 (Java 21) LTS- Record patterns, pattern matching for switch, virtual threads, String templates, unnamed classes and main methods
• Java SE 22 (Java 22)

Java Environment

JDK

• package of tools and runtime needed for java application development such as compiler, debugger etc + JRE.

JRE

• package of tools that enables execution of java applications, includes JVM, libraries etc.

JVM

• a virtual machine which is used to execute the java programs.

Environment Variables

• JAVA_HOME
• CLASSPATH - default value . i.e current directory, preferred