JAVA构造器调用顺序

参考：On Java 8

1. 基类构造器被调用。这个步骤重复递归，直到根基类的构造器被调用，然后是它的派生类，以此类推，直到最底层的派生类构造器被调用。
2. 按声明顺序初始化成员。
3. 最终调用派生类的构造器。

例子：

// polymorphism/Sandwich.java
// Order of constructor calls
// {java polymorphism.Sandwich}
package polymorphism;

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

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

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

输出:

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