Part 1: Java Environment Configuration Guide

1. Download the JDK
2. Download a compiler

   • vscode

     • Lightweight, requires configuration
     • Supports many languages, and there are many plugins too
     • Free
     • The best IDE in the universe!! Not really!!

   • Intellij IDEA

     • Bloated, ready to use right after downloading
     • Suitable for projects

   • Lightly

     • Cloud storage, ready to use right after downloading

   • Eclipse

     • Haven't really used it
     • Free and open source
     • Low system requirements

   • MYEclipse

     • Haven't really used it

   • Jbuilder

     • Haven't used it

   • NetBeans

     • Haven't really used it
     • Free and open source
     • I heard it has a powerful plugin marketplace, though it uses quite a lot of memory

Part 2: Basic Syntax and Comments

Basic Syntax

package com;

public class Helloworld {
    public static void main(String[] args) {
        System.out.println("Hello World！");
    }
}

Comments

/*
	Multi-line comment
*/

// Single-line comment

/**
* Documentation comment
* You can write multiple sentences
*/

Common Data Types

1. Integers

   • For example: 66, 88, -88, -66

2. Decimals

   • For example: 1.1, -1.2

3. Characters

   • For example: A, O, I
   • In code you write: 'A', 'O', 'I'; single quotes are required, and only one character is allowed

4. Strings

   • For example: I love you, "I love you", "HelloWorld"
   • In code you must use double quotes, and the content can be anything

5. Boolean values

   • For example: true and false
   • In code you write: false, true
   • There are only these two values in code, where false means "false" and true means "true"

6. Null value

   • For example: NULL
   • In code it is written as: Null
   • In a program it is a special value; a null value represents emptiness.

7. Special characters

   • \n means a line break
   • \t means a tab key was pressed, roughly leaving a gap of two characters

Variables

1. Variable definition and format

   • A variable is used to store a piece of data; in essence, it is a region in memory
   • 数据类型 变量名 = 数据;

2. Advantages of variables

   • They can be used to remember the data you want to process, making the code you write more flexible and easier to manage

3. Characteristics of variables

   • The data stored in a variable can be replaced

4. Using variables

   • A variable must be declared before it can be used, e.g.: int age = 10;
   • A variable of a certain type can only store data of that type.
     • The difference between int and double
   • Variables have an access scope; a variable is valid within the first {} block from where it is defined. Also, multiple variables defined in the same scope cannot have the same name.

   • 

   • You can declare a variable without assigning a value, but it needs a value when you use it

        int age = 10;
        System.out.println(age);
        age = 11;
        System.out.println(age);
        age = age + 1;
        System.out.println(age);
        
        结果为： 
11
12
13

As you can see, the data in a variable can be replaced

Keywords and Identifiers

Keywords

Identifiers

Composition

1. Digits and letters
2. The underscore _
3. The dollar sign $

Requirements

1. Cannot start with a digit
2. Cannot use a keyword as a name
3. Case-sensitive

Conventions

1. Must satisfy the naming rules
2. It is recommended to use English
3. Make it meaningful
4. Start with a lowercase letter and follow camelCase, e.g.: int studyNumber = 1;

Basic Syntax