Java Programming Idea (4th edition) initialization of static data

No matter how many objects are created, static data always consumes only one copy of storage space . The static keyword cannot be applied to local variables, so it can only be used for fields. If a domain is a static base type field and does not initialize it, it will get a standard initial value for the base type, and if it is a reference to an object, the default initializer is null. Examples are as follows:

Package Test;class bowl{bowl (int marker) {System.out.println ("Bowl (" +marker+ ")");} void F1 (int marker) {System.out.println ("F1 (" +marker+ ")");}} Class Table{static Bowl bowl1=new Bowl (1); Table () {System.out.println ("table ()"); Bowl2.f1 (1);} void F2 (int marker) {System.out.println ("F2 (" +marker+ ")");} Static Bowl bowl2=new Bowl (2);} Class Cupboard{bowl Bowl3=new Bowl (3); static Bowl bowl4=new Bowl (4); Cupboard () {System.out.println ("cupboard ()"); Bowl4.f1 (2);} void F3 (int marker) {System.out.println ("F3 (" +marker+ ")");} Static Bowl bowl5=new Bowl (5);} public class Static {public static void main (String args[]) {System.out.println ("Creating New Cupboard () in main"); new CUPB Oard (); System.out.println ("Creating New Cupboard () in main"); new cupboard (); Table.f2 (1); cupboard.f3 (1);} Static table Table=new table (), Static cupboard cupboard=new cupboard ();

The introduction of the bowl class allows you to see the creation of classes. The table class and the cupboard class include static data members of type Bowl in their class definitions. Note that before a static data member is defined, the cupboard class first defines a non-static data member Bowl3 of the bowl type.

Output Result:

Visible from the output, static initialization occurs only at the necessary time,If you do not create a Table object and do not reference TABLE.BOWL1 or TABLE.BOWL2, then static bowl BOWL1 and BOWL2 will never be created. only the first table object is created (or the first time the static data is accessed), they before it is initialized .。 thereafter, Static objects will no longer be initialized。

From the output, it is known that the order of initialization is a static object (provided that they have not been initialized because of the previous object creation) and then non-static objects.

Java Programming Idea (4th edition) initialization of static data