Static code block, construction code block, construction method, static code Construction Method

Static code block, construction code block, construction method, static code Construction Method

 

 

Run the following code and observe the result:

Package com. test; public class HelloB extends HelloA {public HelloB () {}{ System. out. println ("I'm B class");} static {System. out. println ("static B");} public static void main (String [] args) {new HelloB () ;}} class HelloA {public HelloA () {}{ System. out. println ("I'm A class");} static {System. out. println ("static ");}}

The result is as follows:

Static Astatic BI'm A classi' m B class

 

 

Resolution:

1. Static code block: it is initiated in step 3 of the class loading process. The main purpose is to grant the class variable an initial value.

2. Construct a code block: it is independent and must be attached to a carrier for running. Java puts the constructed code block in front of each constructor to instantiate some common instance variables and reduce the amount of code.

3. constructor: Used to instantiate a variable.

 

Summary:

1 is a class level, and 2 and 3 are instance-level. Therefore, 1 must take precedence over 2 and 3.

The execution sequence is 1> 2> 3;