[Java] [20160707] Java introduction, 20160707 java

[Java] [20160707] Java introduction, 20160707 java

The earliest name of Java was "oak" and later renamed "Java ".

 

Java was first owned by Sun and later acquired by Oracle.

 

The most primitive "oak" is interactive development for TV/oven/home electronics products (Interactive Development can be understood as "interactive operation", "Interactive Operation" is similar

Current "Smart Home.

 

Java versions: JavaME, JavaSE, and JavaEE are Java Micro Edition, Java Standard Edition, and Java Enterprise Edition respectively.

 

Java features: Object-oriented/portability (JVM achieves portability)/robustness/distributed/multithreading ("Threads" can be understood as "lightweight processes...

 

Java is a special high-level language. It has both the characteristics of "explanatory language" and "Compiling language", because it is compiled first, the process of subsequent interpretation.

 

Java Workflow: Java source file (. java file)> compiled by the Java compiler> bytecode file (. class file)>

Machine code for a specific platform> classloaders> loaded to JVM by classloaders> interpreted by JVM to the operating system> executed by the operating system.

 

Compile a helloworld.java file and compile it into a non-specific platform (operating system) through the javac.exe interpreter.

Machine code HelloWorld. class file.

 

Of course, this machine code cannot be executed, and the Java interpreter (java.exe) is used for execution.

 

However, java.exe does not have the ability to interpret it. It calls JVM (Java Virtual Machine) to interpret it as a machine code applicable to the current platform.

 

Java: Java is an explanatory language.

 

JVM is composed of the instruction set, registers, stacks, spam processors, and methods. JVM has three areas: local variable area, execution environment area, and operand area.

 

Java class library: standard class library and developer's own class library

 

Java "package": it is essentially in the form of folders, used to organize project files.

 

JRE: Java Runtime Environment Chinese: Java Runtime Environment. If you only want to run Java programs, install only JRE.

 

JDK: Java Development Kit (Chinese: Java Development Kit (Tool). To develop a Java program, install JDK.