The difference between the JDK JRE JVM
JDK: Java program compile and run without the JDK environment, the JDK (Java Development Kit) is used to develop a Java application Development Kit, it provides a compilation, run a variety of tools and resources needed for Java applications,
JRE: JRE is a Java Runtime Enviroment is refers to the Java Runtime environment
The JVM: the JVM as the Java Virtual Machine (Java Virtual Machine JVM)
For different crowd: JDK crowd mainly oriented developers, and users of JRE is mainly oriented in Java programs,
Important: the operation of the Java program must have the JRE to run; The JDK is a Java program running environment, provide the necessary development of various resources, tools; The JVM is a Java virtual machine, is made up of computer, is used to calculate,


The principle of Java cross-platform
Java language for each computer system to provide an environment called Java virtual machine to realize cross-platform, Java is not only suitable for single application and web-based application, and can be used to create consumer equipment and accessories such as: mobile phone

The Java API documentation
Difficult problems met in the process of development, in addition to being able to find answers in the network, can also be in the Java API documentation (JDK documentation) to find the answer,


Java development requires the right JDK installation and configuration JDK environment, written in the Java source program should pass compiler for the class bytecode file, to execution on the Java fiction, this work cannot leave the JDK environment,