initialization order

initialization order

■  The general order of class initialization is:

 

1 - First all static items are initialized, in their source code order..

2 - Then all member variables are initialized.

3 - Lastly the constructor is called.

 

■  Below is a simple demonstration program showing class initialization order.  Its output is:

 

1a - Static class variable vstatic initialized first.

1b - Static initialization block ran.

2  - Non-static class variable vnonstatic initialized.

3  - Constructor ran.

 

public class ExecuteDemo {

        public static void main(String[ ] args) {

                        DemonstrateOrder DO = new DemonstrateOrder ( );   }

}

class DemonstrateOrder{

        static String vstatic = verify(" 1a - Static class variable vstatic initialized first." );

        String vnonstatic = verify(" 2  - Non-static class variable vnonstatic initialized." );

        static {System.out.println(" 1b - Static initialization block ran." ); }

 

        static String verify(String s) { System.out.println(s);  return s; }

 

        DemonstrateOrder ( ) {System.out.println(" 3  - Constructor ran." );  }

}

 

■  The general order of initialization for classes with inheritance is:

 

First, parent static items, then child static items

Then parent member variables, followed by the parent constructor

Then child member variables, followed by the child constructor

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