Detailed records of java learning basic grammar

【Preface】

The grammar of java should be learned from the basic grammar first. The Java language is composed of classes and objects, whose objects and classes are composed of methods and Variables, and methods include statementsandexpression.

• Object: (Almost) everything is an object, such as: a panda, his appearance, color, what he is eating, drinking, sleeping and playing

• Class: If everything is an object, then what determines the appearance and behavior of a certain type of object? A class is a template that describes the behavior and state of a class of objects.

• 
  

  class HelloWorld{/*这表示一个类，class后跟的是类名*/}

  Copy after login

• Method: (Method can also be called memberfunction ) Methods can be regarded as behaviors. A class can have many methods. Logical operations, data modification, and all actions are completed in methods.

• Variables: Each object has unique instance variables, and the state of the object is determined by the values ​​of these instance variables.

【First java program】

public class HelloWolrd {    /**
     * 第一个Java程序     */
    public static void main(String[] args) {        // 打印Hello World
        System.out.println("Hello World");
    }

}

Speak about saving and compiling, Run this program

1. Use Notepad to save this code. After saving, change the file name to HelloWolrd.java (remember to display the file suffix) as shown in the figure:

　2. Open the dos window and find the location you saved (for example: my location is D:\HelloWorld)

　3. Switch the drive letter to your file storage directory

　4. Enter javac HelloWorld.java and press Enter. There should be an additional HelloWorld in the HelloWorld folder. class file, this compiles this code

　5. Enter java HelloWorld again and print out Hello World

【Basic Grammar】

1. Case sensitive: Size Writing is sensitive, for example, HelloWorld and helloworld are different

2. Class name: The first letter of the java class name must be capitalized, and the class name is composed of multiple letters like UserNameManage , then the first letter of each word should be capitalized, commonly known as the big camel case nomenclature (ie: Pascal nomenclature)

3. Method name: One word Lowercase, for example: user, the first letter of multiple words is lowercase, starting from the second word, the first letter of each word is capitalized, for example: userNameManage (little camel case nomenclature)

4. Keywords : All lowercase, for example: public

5. Constant: All uppercase, for example: PI

6. Variable : The rules are the same as the method naming

7. Package: All lowercase

[java identifier]

All components of Java require names. Class names, variable names, and method names are all called identifiers.

 1. 只能使用字母、数字、下划线和美元符。

 2. 只能以字母、下划线和美元符开头。也就是不能以数字开头。 

 3. 严格区分大小写，没有长度限制。建议不要太长。

 4. 应该具有特定的意义，关键字不可以用作标识符。

【java修饰符】

Java可以使用修饰符来修饰类中方法和属性。主要有两类修饰符：

• 访问控制修饰符 : default, public , protected, private

• 非访问控制修饰符 : final, abstract, strictfp

【java分隔符】

• 具有：空格、圆括号、花括号、分号等。 

• 每条语句无论一行还是多行都以分号结束。块（Block）是包含在{}里面的多条语句，块可以嵌套。空白插在代码的元素中间：由一个或多个空格组成，也可以由一个或多个tab空格组成多个空行。

【java注释】

 写程序注释是必不可少的一部分。做规范，显条理，对于以后的开发带来了方便。

public class HelloWorld {    
    /**
     * @param args
     * 第一个Java程序
     * 这是文档注释     */
    public static void main(String[] args) {        /*
         * 这是多行注释         */
        System.out.println("Hello World");        // 打印Hello World(这是一个单行的注释)
        System.out.println("Hello World");
    }
    
}

【java关键字】

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