Java: a programming language, development environment, application environment, the deployment environment
Three core mechanism of Java
1. Java Virtual Machine (Java Virtual Machine)
The virtual machine is in the real machine using software simulation implementation of a virtual machine, the Java virtual machine code is stored in. The class file; Each file contains up to a public class
2. The Garbage Collection mechanism (Garbage Collection)
The Java programming language lifted the programmer to cancel the responsibility of the allocated memory, it can provide a system level thread to track every memory allocations, in the Java virtual machine idle cycles, garbage collection threads to check and release the memory that can be released
3. Code Security detection (Code Security)
At runtime, the execution machine. Only the class class files through interactive after use, under normal circumstances is not see its source code. Java, should pass special decompiling tools, can see, this is reflected in the Java runtime environment relative to other languages, to strengthen the security of the code,

The JDK is a Java development kit, including the JRE (is used to construct a Java application developers of software packages, it includes: the Java virtual machine (JVM), Java compiler (javac), Java archive (jar) utility, Java document (javadoc) utility, etc.)
JRE is the JAVA runtime environment, not including development tools, is a subset of the set of the JDK (JRE - JAVA runtime environment, is by the JVM and JAVA platform of core classes and related supporting documents)

1. The JVM is the Java virtual machine, the implementation of the class file
2. The javac compiler
3. The interpretation of the Java interpreter code execution, the Java virtual machine to run the target code (bytecode) explains the concrete platform machine code program
4. The javadoc documentation generator in Java source code by @... Add documentation comments, and then in the generated HTML document
5. Bin where executable files
6. Java db stored D3 (small database, can not)
7. The lib where Java library files
8. The SRC. Zip is the zip file, containing class definition in Java source files
9. The include storage C header file associated