Java subclass and parent class initialization process

When instantiating a subclass, the default constructor of the parent class is called layer by layer from the parent class at the top.

The so-called default constructor is a constructor without parameters. If the parent class does not have a constructor, The subclass must explicitly use super to call a constructor with parameters of the parent class.

Class X {y B = New Y (); X () {system. out. print ("X") ;}} class y {Y () {system. out. print ("Y") ;}} public class app extends X {Y = New Y (); app () {system. out. print ("Z");} public static void main (string [] ARGs) {new app ();}}

CodeThe output is yxyz. Therefore, the Code initialization process is:

1. First, call the constructor of the parent class.

2. initialize the member variables of the class.

3. Finally, call your own constructor.