Programming in Java
Object Oriented in Java
Advanced topics in Java
Tutorials 
JDK, JRE, JVM
JDK
Java Development Kit (JDK) combines JRE and devlopment tools such as java compiler etc. Once we install JDK, we can create java applications and applets too.
JDK Also contains JVM and some JAR (Java Archive) files such as rt.jar
To Download JDK, use the following link.
https://www.oracle.com/technetwork/java/javase/downloads/jdk8-downloads-2133151.html
JRE
JRE stands for Java Runtime Environment. JRE is the subset of JDK and it is the prerequisite to run Java Applcations. JRE is the implementation of JVM and also exists physically.
Different OS based JRE can be downloaded from the follwing link.
https://www.oracle.com/technetwork/java/javase/downloads/jre8-downloads-2133155.html
Class Loader
The Java Class Loader is a part of the Java Runtime Environment that dynamically loads Java classes into the Java Virtual Machine.
Class Loaders are of following types.
a. Bootstrap class loader
b. Extensions class loader
c. System class loader
JVM
JVM stands for Java Virtual Machine . It is known as virtual because it does not exists physically.
By using JVM, we can run other programs written in different programming languages but compiled to Java bytecode.
Main functioning of the JVM is following :
1. To load the code
2. Verifies it
3. Executes code
4. And Provides runtime environment.