Java subclasses, static code blocks in the parent class, fields, non-static code blocks, fields, and initialization order and number of constructors

The order of data initialization in a class is one of the questions that the interviewer likes very much, this article uses an example to introduce the Java sub-class, the parent class static code block, the field, the non-static code block, the field and the constructor execution order and the number of times.

First, the package structure

Cat Inheritance Animal

The runner contains the main function, the program entry

The Sing class is used primarily to print the sequence number of the execution

Second, the Code

 Public classAnimal {Sing S1=NewSing (1, "Animal\tnot static field"); StaticSing s2=NewSing (2, "animal\tstatic field"); StaticSing S3;        Sing S4;                Sing S5; Static{S3=NewSing (3, "Animal\tstatic code area"); } {S4=NewSing (4, "Animal\tnot Static code area"); } Animal () {S5=NewSing (5, "Animal\tconstructor"); }    }

 Public classCatextendsAnimal {Sing S1=NewSing (1, "Cat\t\tnot static field"); StaticSing s2=NewSing (2, "cat\t\tstatic field"); StaticSing S3;    Sing S4;        Sing S5; Static{S3=NewSing (3, "Cat\t\tstatic code area"); } {S4=NewSing (4, "Cat\t\tnot Static code area"); } Cat () {S5=NewSing (5, "Cat\t\tconstructor"); }}

 Public class Sing {    Sing (int  mark,string flag) {        System.out.println (Mark+ "+flag);}    } 

 Public class Runner {    publicstaticvoid  main (string[] args) {        System.out.println ("+++++++++++++++++++++first+++++++++++++++++++++++++++++");         New Cat ();        System.out.println ("+++++++++++++++++++++second++++++++++++++++++++++++++++");         New Cat ();    }}

III. Results of implementation

+++++++++++++++++++++first+++++++++++++++++++++++++++++
2 animal    static field
3 animal     static Code Area
2 cat        static field
3 cat   & nbsp;    static Code Area
1 animal    not static field
4 animal     Not static code area
5 animal    constructor
1 cat        not static Field
4 cat        not static code area
5 cat         Constructor
+++++++++++++++++++++second++++++++++++++++++++++++++++
1 animal    not static Field
4 animal    not static code area
5 animal    constructor
1 cat         not static field
4 cat        not static code area
5 cat        constructor

Iv. Summary

Initialization order: Parent static field-"Parent static code block-" Subclass static field-"subclass static code block-" Parent non-static field-"Parent non-static code block-" Parent construction-"Subclass non-static field-" Subclass non-static code block-"sub-class construction

Follow these guidelines:

1, static > Non-static

2. Parent Class > Subclass

3. Fields > Code blocks > Constructors

4, static field, static code block in the program life cycle only initialized once

Java subclasses, static code blocks in the parent class, fields, non-static code blocks, fields, and initialization order and number of constructors