Java elementary basic code block

• The role of the code block: used to initialize classes, objects
• If the code block is modified, only static can be used.
• Classification: static code block and non-static code block

1. Static code block

• There can be output statements inside
• Executed as the class is loaded, and only once
• Role: initialize the information of the class
• If multiple static code blocks are defined in a class, they are executed in the order of declaration
• The execution of static code blocks takes precedence over the execution of non-static code blocks
• Only static properties and static methods can be called in static code blocks, and non-static structures cannot be called

2. Non-static code block

• There can be output statements inside
• Execute as the object is created
• Every time an object is created, a non-static code block is executed
• Function: When creating an object, initialize the properties of the object, etc.
• If multiple non-static code blocks are defined in a class, they are executed in the order of declaration
• Non-static code blocks can call static properties, static methods, or non-static properties, non-static methods

3. Code example

/**
 * @Author: YuShiwen
 * @Date: 2020/11/17 3:51 PM
 * @Version: 1.0
 */
public class BlockTest {
    
    
    public static void main(String[] args) {
    
    
        System.out.println("main方法中输出语句："+Student.school);

        Student student1 = new Student();
        Student student2 = new Student();

        System.out.println("main方法中输出语句："+Student.school);
    }
}

class Student{
    
    
    String name;

    int age;

    static String school = "Yangtze University";

    public Student() {
    
    
    }

    public Student(String name, int age) {
    
    

        this.name = name;
        this.age = age;
    }

    //静态代码块
    static {
    
    
        System.out.println("static block1");
    }
    static {
    
    
        System.out.println("static block2");
        school = "Yangtze University !!!";
        hobby();
        //静态代码块中不可以调用非静态结果
        //study();
    }

    //非静态代码块
    {
    
    
        System.out.println("block1");
    }
    {
    
    
        System.out.println("block2");
        //调用非静态结构
        name = "YuShiwen";
        age = 21;
        study();
        //调用静态结构
        school = "~~ Yangtze University ~~";
        hobby();
    }

    //方法
    public void study(){
    
    
        System.out.println("我是一个爱学习的人！");
    }

    public static void hobby(){
    
    
        System.out.println("我喜欢健身！");
    }

    @Override
    public String toString() {
    
    
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

Output result:

static block1
static block2
我喜欢健身！
main方法中输出语句：Yangtze University !!!
block1
block2
我是一个爱学习的人！
我喜欢健身！
block1
block2
我是一个爱学习的人！
我喜欢健身！
main方法中输出语句：~~ Yangtze University ~~

Process finished with exit code 0

Sample code analysis: