继承与初始化和构造器的调用

调用构造器要遵循以下顺序：
1、调用基类构造器。这个步骤会不断反复递归下去，首先是构造这种层次结构的根，然后是下一层导出类，等等，直到最底层的导出类。
2、按声明顺序调用成员的初始化方法。
3、调用导出类构造器的主体。

继承与初始化
请看下例：

class Insect {
private int i = 9;
protected int j;// protected static int j; 上转型时 j 不再初始化，为39

Insect() {
System.out.println("i=" + i + ",j=" + j);
j = 39;
}

private static int x1 = printInit("static Insect.x1 initialized");

static int printInit(String s) {
System.out.println(s);
return 47;
}
}

public class Beetle extends Insect {
private int k = printInit("Beetle.k initialized");

public Beetle() {
System.out.println("k=" + k);
System.out.println("j=" + j);
}

private static int x2 = printInit("static Insect.x2 initialized");

public static void main(String[] args) {
System.out.println("Beetle constructor");
Beetle b = new Beetle();
System.out.println();
Insect a = new Beetle();
}
}

运行结果：

static Insect.x1 initialized
static Insect.x2 initialized
Beetle constructor
i=9,j=0
Beetle.k initialized
k=47
j=39

i=9,j=0
Beetle.k initialized
k=47
j=39

构造器的调用顺序
请看下例：

class Meal {
Meal() {
System.out.println("Meal()");
}
}

class Bread {
Bread() {
System.out.println("Bread()");
}
}

class Cheese {
Cheese() {
System.out.println("Cheese()");
}
}

class Lettuce {
Lettuce() {
System.out.println("Lettuce()");
}
}

class Lunch extends Meal {
Lunch() {
System.out.println("Lunch()");
}
}

class PortableLunch extends Lunch {
PortableLunch() {
System.out.println("PortableLunch()");
}
}

public class Sandwich extends PortableLunch {

private Bread b = new Bread();
private Lettuce l = new Lettuce();
private Cheese c = new Cheese();

public Sandwich() {
System.out.println("Sandwich()");
}

public static void main(String[] args) {
new Sandwich();
}
}

运行结果：

Meal()
Lunch()
PortableLunch()
Bread()
Lettuce()
Cheese()
Sandwich()