复杂对象调用执行顺序

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class Meal {
    Meal() {
        System.out.println("Meal()"); // 5
    }
}

class Lunch extends Meal {
    private static Demo4 demo4 = new Demo4();  //1
    private Demo demo = new Demo();  // 6
    static {
        System.out.println("lunch static code ");//2
    }
    Lunch() {
        System.out.println("Lunch()"); //7 
    }
}
public class Sandwich extends Lunch {
    private static Demo3 demo3 = new Demo3();//3
    private Demo2 demo2 = new Demo2(); // 8
    static{
        System.out.println("Sandwich static code");//4
    }
    Sandwich() {
        System.out.println("Sandwich()");  // 9
    }

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

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

class Demo2 {
    Demo2() {
        System.out.println("Demo2()");
    }
}

class Demo3 {
    Demo3() {
        System.out.println("Demo3()");
    }
}

class Demo4 {
    Demo4() {
        System.out.println("Demo4()");
    }
}

观察上面的执行顺序，可得:

1. 首先调用基类的静态成员变量的初始化方法，调用基类的静态代码块，逐层这样调用，直到最低层
2. 调用基类的成员变量初始化方法，调用基类的构造函数，逐层这样调用，直到最低层