Introduction to Java

Java was released by Sun Microsystems in 1995 and is now maintained by Oracle and a large open-source community. It's one of the most widely used languages in the world, especially for big business systems.

Where Java is used

Example	Where it runs
Android	phone, tablet and TV apps, written in Java or Kotlin on the same platform
Spring	the back ends of banks, insurers, airlines and online shops
Hadoop	storing and processing huge data sets, on the Java platform
Kafka	streaming data between systems, on the Java platform
IntelliJ IDEA	the editor many Java developers use, itself written mostly in Java

Games too: Minecraft's original edition is written in Java.

Write once, run anywhere

Java source code is compiled into bytecode, not machine code for one particular processor. Bytecode runs on the Java Virtual Machine (JVM), which exists for Windows, macOS, Linux and more, so the same compiled program runs everywhere.

Main.java  --javac-->  Main.class (bytecode)  --JVM-->  runs on any OS

Your first look

public class Main {
    public static void main(String[] args) {
        System.out.println("Hello, Java!");
    }
}

The next lesson explains every word. For now, notice that Java is strict and explicit: everything lives inside a class, and every statement ends with a semicolon.

Why learn Java?

• Strong typing catches many mistakes before the program runs.
• Object-oriented design scales to very large codebases.
• Huge job market and a mature ecosystem of libraries and tools.