How to understand: common code block, construction block, static block? What does it matter?

Catalog

Common code block （ Local code block ）

Tectonic block （ Instance code block ）

A static block （ Static code block ）

What's the relationship between them ？

Example ：

analysis ：

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Common code block （ Local code block ）

         The definition is used in the method { } Enclosed code block （ In general { } It is called code block , Just no segmentation ）, It's a normal code block , Also called native code blocks  .（ Not often , Not often ）

for example ：

public class Test {
    public static void main(String[] args){
        
        {
            System.out.println(" Local code block ！");    
        }
        
    }
}

---

Tectonic block （ Instance code block ）

        The instance code block is defined inside the class , The outside of the method , Members of the instance can be initialized

for example ：

class Student{
    // Member variables 
    public String name;
    public int score;
    // Class variables 
    public static String classes = " The rockets 6 class ";
    // Class method 
    public static void fun1(){
        Student stu = new Student();
        stu.name = "jay";           // correct 
        System.out.println(" Class method ");
    }
    // Member method 
    public void fun2(String name, int score){
        this.name = name;
        this.score = score;
    }
    // Instance code block 
    {
        this.name = "jay";
        System.out.println(" Instance code block !");
    }
}

---

A static block （ Static code block ）

         Static code blocks are defined inside the class , The outside of the method , Members of the instance can be initialized

for example ：

class Student{
    // Member variables 
    public String name;
    public int score;
    // Class variables 
    public static String classes = " The rockets 6 class ";
    // Class method 
    public static void fun1(){
        Student stu = new Student();
        stu.name = "jay";           // correct 
        System.out.println(" Class method ");
    }
    // Member method 
    public void fun2(String name, int score){
        this.name = name;
        this.score = score;
    }
    // Instance code block 
    {
        System.out.println(" Instance code block !");
    }
    // Static code block 
    static{
        classes = "16 class ";
        System.out.println(" Static code block !");
    }

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What's the relationship between them ？

Example ：

Situation 1 ： See what the following code will execute ？

class Student{
    // Member variables 
    public String name;
    public int score;
    // Construction method 
    public Student(){
        System.out.println(" Construction method !");
    }
    // Class variables 
    public static String classes = " The rockets 6 class ";
    // Class method 
    public static void fun1(){
        Student stu = new Student();
        stu.name = "jay";           // correct 
        System.out.println(" Class method ");
    }
    // Member method 
    public void fun2(String name, int score){
        this.name = name;
        this.score = score;
    }
    // Instance code block 
    {
        System.out.println(" Instance code block !");
    }
    // Static code block 
    static{
        System.out.println(" Static code block !");
    }
}
public class Test {
    public static void main(String[] args){
        Student stu = new Student();
    }
}

Case 1 operation results ：

Situation two ： See what the following code will execute ？

class Student{
    // Member variables 
    public String name;
    public int score;
    // Construction method 
    public Student(){
        System.out.println(" Construction method !");
    }
    // Class variables 
    public static String classes = " The rockets 6 class ";
    // Class method 
    public static void fun1(){
        Student stu = new Student();
        stu.name = "jay";           // correct 
        System.out.println(" Class method ");
    }
    // Member method 
    public void fun2(String name, int score){
        this.name = name;
        this.score = score;
    }
    // Instance code block 
    {
        System.out.println(" Instance code block !");
    }
    // Static code block 
    static{
        System.out.println(" Static code block !");
    }
}
public class Test {
    public static void main(String[] args){
        System.out.println(Student.classes);
    }
}

Case 2 operation results ：

analysis ：

• The order of their execution is ： Static code block -> Instance code block -> Construction method （ No matter where the code block is , This is the order ！ If there are multiple static , Just look at the definition order ）
• As long as the class is loaded , Static code blocks are executed
• If the object is not instantiated, it will only execute statically
• If there are multiple instances , It depends on the order of definition
• If the object is not instantiated , Static code blocks are executed only once