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 main
Bowl(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。