Java language Overview

First, the basic knowledge of the computer

Computer: An electronic computer, commonly known as computers. Electronic components, mainly used in: Scientific computing, data analysis, computer-aided design, artificial intelligence, network, multimedia

Hardware: External (monitor, keyboard mouse, mainframe box)
Internal (motherboard, CPU, memory strip, power, hard drive)
Von. Neumann system = operator (computer capable of computing) + controller (computer capable of controlling printer) + memory + input device + output device

Software: System software (provides environment for application software) Windows, Mac, Linux, Android, IOS
Application software (to meet people's needs, students learn is to develop application software)

keyboard shortcut keys
Window + R (Opens the Run dialog box)
CTRL + A (select all), CTRL + C (copy), CTRL + V (paste), CTRL + X (cut), CTRL + Z (undo), Ctrl + S (SAVE)

DOS command
CD directory: Represents the entry directory (. Current directory 、.. Top-level directory, specific path D:\java\jdk7\bin)
MD Folder name: Create Folder
Rd Folder name: Delete empty folder, add parameter/s/q non-empty folder
Del file name: Delete the specified file, del *.txt: Delete matches the corresponding multiple files
CLS: Clear Screen
Exit: Exit

Ii. Overview of the Java language

The Java language is cross-platform and the JVM can run on different operating systems. The JVM is inside the JRE, JRE = JVM + Class library. JDK = JRE + development tools

Third, JDK download and installation (master)

Oracle acquired Sun and later downloaded the JDK to Oracle's website.

First D:\ new Java folder, inside the new jdk7, install JDK when you specify directory to this, you can omit the JRE installation

Iv. cases of HelloWorld

Class Helloworld {
public static void Main (string[] args) {
System.out.println ("This is my first Java program development");
}
}

Compile is Javac file name: Javac Helloworld.java

Run is a Java class name (class name and file name is the same): Java Helloworld

V. Configuration of environment variables

No environment variable program can run correctly, but trouble.

Path: The Java development tool can be used under any path, using the

Classpath: The program is running in the current directory, and will continue after

Vi. notes

Documentation notes: Manual, Format is the slash star starts, the star slash ends, each line starts with a *, and the first star of each row is to form a column. Alt + mouse Up and down (arrow keys)

Can be used in front of the class, before the Main method

Single-line comment: Double slash, multiline comment: Slash star starts, star Slash ends

Note You can now simply drain the error, debug the program

Seven, key words

All lowercase, with special meanings. You don't have to remember to practice a few more times.

Eight, identifiers

Name a class, package, interface, method, constant, variable

Case letters, numbers, $ and _

Cannot start with a number

Can't use keywords

Java language Overview