Different Java Learning (i) basic knowledge

Previous Python machine learning found that when the amount of data is getting larger and smaller, the simple Python processing is difficult to meet,

Hadoop has to be used for parallel processing of data, and Hadoop is written in Java, so I started Java learning.

Here are the Learning notes

A total of 9 chapters, the general idea of the chapter is: why---> What---> How to do.

about why?

In short, effective processing of data.

What about?

Then welcome to the world of reptiles.

First, basic knowledge

1. Software development

A: What is software?

Software: A collection of computer data and instructions organized in a specific order.

Common software: System software: such as dos,windows,linux, etc.,

Application software: such as Minesweeper, Thunder, QQ and so on.

B: What is development?

Authoring software

2. Human-Computer Interaction

A: The advent of software enables better interaction between people and computers.

B: Interactive mode:

Graphical interface (graphical user Interface GUI)

This method is simple and intuitive, the user is easy to accept, easy to operate.

Command line Interface CLI

You need to have a console, enter specific instructions, and let the computer do some work.

More trouble, need to record some commands.

3. Command line mode

DOS command line, a common command in the course.

Dir: Lists the files and folders in the current directory

MD: Creating a Directory

RD: Deleting a directory

CD: Enter the specified directory

Cd.. : Back to the top level directory

CD \: Go back to the root directory

Del: Delete Files

Exit: Launch DOS command line

4. Computer language

A: Through the DOS command line demonstration, discovered the original operation computer on how the computer speaks.

B: We tell it what to do and what it can do. The premise is that we and what it says must be identified before it can be. This is the computer language.

4.1. What is computer language?

A: Language: It is a way of communication between people.

For example: Chinese and Chinese communicate in Chinese.

And the Chinese people to communicate with Koreans, we must learn Korean.

B: Computer language: The way people communicate with computers.

If the person wants to communicate with the computer, then must study the computer language.

There are many kinds of computer languages, such as: C,c++,java, etc.

4.2. Overview of the Java language

A: It is a high-level programming language introduced by Sun (Stanford University Network, Stanford University web Company) in 1995.

B: is an Internet-facing programming language.

C: As Java technology continues to mature in the web, it has become the preferred development language for Web applications.

D: It is easy to learn, completely object-oriented, safe and reliable, platform-independent programming language.

E: three technical architectures

EE (Java 2 Platform Enterprise Edition) Corporate Edition

J2SE (Java 2 Platform standard Edition) edition

J2ME (Java 2 Platform micro Edition) Mini version

F: Language Features: cross-platform

What is the principle?

Just on the operating system that needs to run the Java application,

Install a Java Virtual machine (JVM Java VM) first.

The JVM is responsible for the operation of the Java program in the system.

4.3, the Java language environment construction

A: Clear what is the JRE (Java runtime enviroment) Java Runtime Environment, JDK (Java Development Kit) Java Development Kit

B: Download JDK

C: Install JDK

D: Configure environment variables

E: Verify Success

4.4. Java Program development experience--hello World

Write the Java code in a file with a. java extension.

Compile the. java file by using the Javac command.

The generated class file is run with the Java command.

In short: write-and-compile-run

4.5 Configuring Classpath

Classpath Lookup Order: First in path definition of the paths, and then to the current search;

Path Lookup order: First in the current search, then to the path to find.

This chapter focuses on:

Features of JDK,JRE,JVM

The configuration of environment variables path and classpath as well as the role.

Java program writing, compiling, running steps.

In the configuration, write, compile, run the common errors and workarounds in each step.

In the next chapter we will explain the basics of the Java language composition

Different Java Learning (i) basic knowledge