Basic structure of Java program

WYH grass sample 2021-01-23 11:35:33
basic structure java program


complete Java Program, its basic structure
/**
* Comments that can be used to automatically create documents
*/
public class Hello {
public static void main(String[] args) {
// Output text to the screen :
System.out.println("Hello, world!");
/* Multiline comments start
The comment
End of comment */
}
} // class End of definition

because Java It's an object-oriented language , The basic unit of a program is class,class Is the key word , What is defined here class The name is Hello:

public class Hello { // The name of the class is Hello
// ...
} // class End of definition
Requirements for class names
  • The class name must start with an English letter , Followed by a letter , A combination of numbers and underscores
  • It's customary to start with a capital letter

be aware public It's the access modifier , It means that we should class Is an open .
Don't write public, It also compiles correctly , But this class will not be able to execute from the command line .
stay class Inside , Several methods can be defined (method):

public class Hello {
public static void main(String[] args) { // The name of the method is main
// method code ...
} // End of method definition
}
  • Method defines a set of execution statements , The code inside the method will be executed in sequence .
  • The method name here is main, The return value is void, Indicates that there is no return value .
  • We noticed that public In addition to being able to decorate class Outside , You can also modify methods . And keywords static It's another modifier , It represents static methods , We'll talk about the types of methods later , at present , We just need to know ,Java The method specified in the entry procedure must be static , Method name must be main, The parameter in brackets must be String Array .
  • There are also naming rules for method names , Name and class equally , But the initials are lowercase :
    Be careful
Inside the method , Statement is the real execution code .Java Each line of the statement must end with a semicolon :

stay Java In the program , Annotation is a kind of text for people to read , Not part of the program , So the compiler automatically ignores comments .
Java Yes 3 Species notes , The first is a single line comment , Start with a double slash , Until the end of the line :

// This is the note ...

And multiline comments with / It starts with an asterisk , With / end , How much can I do :

/*
This is the note
blablabla...
This is also the note
*/

There's a special kind of multiline annotation , With /** start , With */ end , If there are many lines , Each line usually begins with an asterisk :

/**
* Comments that can be used to automatically create documents
*
* @auther liaoxuefeng
*/
public class Hello {
public static void main(String[] args) {
System.out.println("Hello, world!");
}
}

This special multiline annotation needs to be written in the definition of classes and methods , Can be used to automatically create documents .
Java There is no clear format requirement for the program , More spaces or carriage returns do not affect the correctness of the program , But we need to develop good programming habits , Observe Java Community agreed coding format .

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