Initialization sequence of java classes

In Java, when we create a new object, the members, initialization blocks and constructors in the object are loaded in a certain order. See the picture below:

1. Single class (no base class) ):

public class Parent {

static String staticStr = "Parent class static variable";

private String str = "Parent class member variable";

static {

System.out. println(staticStr);

　System.out.println("Parent class static initialization block");

}

{

System.out.println(str);

System.out.println(" Parent class initialization block");

}

public Parent() {

　　System.out.println("Parent class construction");

}

​

public static void main(String[] args ) {

　 new Parent();

                                                                                                                                                                             ;

Parent class initialization Block parent -class structure

/* If you let go of the second line New Parent (), the output result will increase the following content: the parent class member variables

parent -initialization block

parent structure

*/

*/

*/

*/

*/

Single class order: ① Static (members, blocks) > Non-static (members, blocks) > Construction

                                                                                 ② The order of members and blocks depends on "their position before and after they are defined in the class, whoever is first is initialized first" ".

③ Static members or blocks belong to classes, so they are initialized first and will only be initialized once.

                                                                                                                                                                                                                                                 The structure to be executed last.

2. Initialization sequence of inherited classes

class SubClass extends Parent {

static String staticStr = "subclass static variable";

private String str = "subclass member variable";

static {

System.out.println(staticStr);

　System.out.println("Subclass static initialization block");

}

{

System.out.println(str);

　System.out.println("Subclass initialization block");

}

public SubClass() {

　System.out.println("Subclass construction");

}

public static void main(String[] args) {

System.out.println("subclass main method");

　 new SubClass();

}

}

Output: parent class static variable

           Class static initialization block 子 类 static variable static variables

sub -class static initialization block

subcate Main method

parent class variable variables

parent initialization blocks

parent -class member variables Initiative of the initialization block

Inheritance order:

① parent class static (member, block)> sub -class static (member, block)> parent class non -static (member, block) Non-static (members, blocks) > Subclass construction

②Similarly, the order of members and blocks is the same as in a single class

③The parent comes first before the child, but the static (members and blocks) of the subclass precede the parent Non-static classes (members and blocks), because static belongs to the class; for non-static and constructors, it is natural that all the parent classes are loaded, and then the subclasses are loaded.