III. Preparation before developing Java programs

JDK "Java Development Kit": Java Developer kit
JRE "Java Runtime Environment": Java Runtime Environment
JVM "Java Virtual machine": Java VM

JRE: The runtime environment, including the core class libraries required by the JVM and Java programs "If you want to run a Java program that is already developed, just install the JRE."
JDK: is provided to the programmer, which contains the Java development tools, also contains the JRE, when the JDK installed, do not need to install the JRE

The relationship between three persons:
JDK>JRE>JVM, using a Java program developed by the JDK to run to the JVM in the JRE

1. Download the JDK
Www.oracle.com
Java.sun.com

2. Installing the JDK

3. Configure Environment variables
The difference between user variables and system variables: Only the user variables are valid for the current user, and the system variables are valid for all users "to reduce the impact of their own modifications to other users, you can choose to set the user variable", we configure the system variables

Java_home
Path:
Classpath: JDK1.4 version prior to fitting

Function: In order to be able to access the Java SDK directly under any directory "do not need to switch the path to the bin directory every time" to facilitate the development of the program

III. Preparation before developing Java programs