Java is a high-level programming language
In human thought of program design and coding
The computer is composed of hardware + software
Software is used to drive the hardware
Hardware is the electronic equipment, electronic equipment circuit, only use the
0 s and 1 s on behalf of the circuit of electric power and
Sun's development, we are belong to the Oracle (Oracle)
The characteristics of
1. Relatively simple
2. The object-oriented: close to reality logic
3. The cross-platform
Compile once, run anywhere
Computers. Playing games () desk. Put (computer)
Write code that can run on a variety of operating systems
4. Multithreading
Can do different things at the same time "and"
5. Open source (Free)
Open source
3, technical system
Java J2SE (java2 Standard Edition) Standard version: Java
Core infrastructure coreJava
J2EE (java2 Enterprise Edition) Java Enterprise Edition:
Java enterprise development: Java Web development Java Web
J2ME (java2 Micro Edition) Java small version: embedded Java
Type development
Four, version
Java version 1.0 from the beginning, so far, JDK12,
For the Java version, there are two kinds of representation, in July, for example:
JDK 1.7 (Java version)
JDK 7 # products (Java)
Three concepts
1, the JDK
The Java Development Kit Java Development tools, doing Java Development
Must use the JDK
When writing Java code, the necessary software environment,
Java - version JDK | -- -- -- -- -- bin: binary binary storage is a binary file, the role of an executable program bin directory can be used for most software | -- -- -- -- -- the include:. H file, C header file | -- -- -- -- -- the jre: | -- -- -- -- -- the lib: jar package JDK dependencies | -- -- -- -- - the SRC. Zip: part of the Java source code
Written in the Java program code and the basis of all of the base class is derived from
The JDK
2, the JRE
Java Runtime Environment for Java Runtime Environment
Java code is running in the JRE, JRE can exist alone
The JDK includes the JRE
3, the JVM
Java Virtual Machine Java Virtual Machine (JVM)
A virtual operating system, independent of memory space, and the external share
The CPU
The JVM belongs to the JRE
Cross-platform operation
Javac command (Java cross-platform)
Java Compile Compile
Compiler: converts Java file to class files (bytecode file)
Process
Java real execution is a class file
Cross-platform:
Compile once, run anywhere: for class files, can be in any
The operating system to run on
Different operating system, there are differences at the bottom of the Java by not cross-platform
JVM implementation the cross-platform class files
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