Java

Invented in the '90-ies by SUN Microsystems, intended for interactive television.

SE Standard Edition

EE Enterprise Editions, adds tools and classes

ME Micro Edition / JAVA Applets were discontinued

SUN Microsystems acquired by Oracle, license for large companies are now charged per virtual machine.

OpenJDK builds: Microsoft, IBM, Redhat, SAP, Azul, etc

with a JRE runtime and JDK compiles

.java is the source code, needs to have the same name as the class it defines and in the directory mentioned in the package

.class compile java class, this can be run in the runtime.

.jar is a zip file with classes

JAVA_HOME

JRE_HOME

JDK_HOME

Alternatives

google, ibm, microsoft implementations

language vm, memory, bytecode

java scala ruby groovy

licensing

object oriented class

/com/janmg/hello.java
package com.janmg
static void main(args)
{
   System.out.println("Hello World");
}

javac -cp / /com/janmg/hello.java
java -cp . hello

Maven

LOG4J