Java中构造方法的执行顺序

一、先执行内部静态对象的构造方法，如果有多个按定义的先后顺序执行；静态对象在构造的时候也是也先执行其内部的静态对象。

二、再调用父类的构造方法（父类还有父类的话，从最开始的基类开始调用），如果没有明显指定调用父类自定义的构造方法，那么编译器会调用默认的父类构造方法super()。但是如果要调用父类自定义的构造方法，要在子类的构造方法中明确指定。

三、按声明顺序将成员引用对象变量初始化。

四、最后调用自身的构造方法。

下面以一个例子来说明代码如下：

class Animal{
    String name;
    Animal() {
        System.out.println("class Animal");
    }
    Animal(String name){
        this.name = name;
        System.out.println(name + "  class Animal");
        printNumber();
    }

    public void printNumber(){

    }
}

class Fish extends Animal{
    Fish() {
        System.out.println("class Fish");
    }
}

class GoldFish extends Fish {
    GoldFish() {
        System.out.println("class GoldFish");
    }
}

class Cat {
    Cat(){
        System.out.println("class cat");
    }
}

class Rabbit {
    private static int number;
    private static Cat cat = new Cat();
    public Rabbit() {
        number++;
        System.out.println(number + "class rabbit");
    }
}

class Dog extends Animal{
    public int dogNumber;
    private GoldFish goldFish = new GoldFish();
    static  Rabbit blackRabbit = new Rabbit();
    static  Rabbit whiterabbit = new Rabbit();

    public Dog() {
        super("Tom");
        System.out.println("class Dog");
        dogNumber = 10;
        System.out.println("The dog's number is:" + dogNumber);
    }

    public void printNumber(){
        System.out.println("The dog's number is:" + dogNumber);
    }
}

public class TestInheritanceConstructor extends Animal {
    public static void main(String[] args){
        new Dog();  //Test the executive order of constructor
    }
}

class Animal{
	String name;
	Animal() {
		System.out.println("class Animal");
	}
	Animal(String name){
		this.name = name;
		System.out.println(name + "  class Animal");
		printNumber();
	}
	
	public void printNumber(){
		
	}
}

class Fish extends Animal{
	Fish() {
		System.out.println("class Fish");
	}
}

class GoldFish extends Fish {
	GoldFish() {
		System.out.println("class GoldFish");
	}
}

class Cat {
	Cat(){
		System.out.println("class cat");
	}
}

class Rabbit {
	private static int number;
	private static Cat cat = new Cat();
	public Rabbit() {
		number++;
		System.out.println(number + "class rabbit");
	}
}

class Dog extends Animal{
	public int dogNumber;
	private GoldFish goldFish = new GoldFish();
	static  Rabbit blackRabbit = new Rabbit(); 
	static  Rabbit whiterabbit = new Rabbit(); 
	
	public Dog() {
		super("Tom");
		System.out.println("class Dog");
		dogNumber = 10;
		System.out.println("The dog's number is:" + dogNumber);
	}
	
	public void printNumber(){
		System.out.println("The dog's number is:" + dogNumber);
	}
}

public class TestInheritanceConstructor extends Animal {
	public static void main(String[] args){
		new Dog();	//Test the executive order of constructor 
	}
}

执行结果：

class cat 
1class rabbit
2class rabbit
Tom  class Animal
The dog's number is:0
class Animal
class Fish
class GoldFish
class Dog
The dog's number is:10

解释：

输出：class cat  是因为Dog类中有静态成员。而静态成员所在的类Rabbit中又有静态成员。所以最先执行它。验证第 一句。

输出：1class rabbit 和 2class rabbit 是执行类Rabbit构造函数。

输出：Tomclass Animal 执行父类的构造函数，因为用super("")。

输出：The dog's number is:0 可以看出子类的dogNumber还是默认值0

输出：class Animal 和 class Fish 和 class GoldFish是构造goldFish引用对象类型。验证第三句。

输出：class Dog  和The dog's number is:10是执行自己的构造函数。