构造器初始化

初始化顺序

    在类的内部，变量定义的先后顺序决定了初始化的顺序。即使变量定义散布于方法定义之间，它们仍旧会在任何方法（包括构造器）被调用之前得到初始化。

请看下例：

//OrderOfInitialization.java
class Window {Window(int marker) {System.out.println("Window(" + marker + ")");}}class House {Window w1 = new Window(1);House() {System.out.println("House()");w3 = new Window(33);}Window w2 = new Window(2);void f() {System.out.println("f()");}Window w3 = new Window(3);}public class OrderOfInitialization {public static void main(String[] args) {House h = new House();h.f();}}

运行结果：

Window(1)Window(2)Window(3)House()Window(33)f()

静态数据的初始化

    无论创建多少个对象，静态数据都只占用一份存储区域。static关键字不能应用于局部变量，因此它只能作用于域。

请看下例：

//StaticInitialization.java
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 StaticInitialization {public static void main(String[] args) {System.out.println("Creating new Cupboard() in main");new Cupboard();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();}

运行结果：

Cupboard()f1(2)Creating new Cupboard() in mainBowl(3)Cupboard()f1(2)f2(1)f3(1)

    由输出可见，静态初始化只有在必要时刻才会进行，静态对象不会再次被初始化。

    初始化的顺序是先静态对象，而后是“非静态”对象。