java继承时候类的运行顺序问题

• Z时代
• 2024-01-10
• 分类：综合

子类在继承父类后，创建子类对象会首先调用父类的构造函数，先运行父类的构造函数，然后再运行子类的构造函数，例如以下所看到的：

class Father{
	public Father(){
		System.out.println("I am father");
	}
}
public class Child extends Father{
	public Child(){	
		System.out.println("I am child");
	}
	public static void main(String[] args) {
		Father f=new Father();
		Child c=new Child();
	}
}

当父类有带參数的构造函数时，子类默认是调用不带參数的构造函数，例如以下所看到的：

class Father{
	public Father(){
		System.out.println("I am father");
	}
	public Father(String name){
		System.out.println("I am father,My name is "+name);
	}
}
public class Child extends Father{
	public Child(){	
		System.out.println("I am child");
	}
	public static void main(String[] args) {
		Father f=new Father("Apache");
		Child c=new Child();
	}
}

若想子类调用父类带參数的构造函数，须要用super()函数申明，例如以下：

class Father{
	public Father(){
		System.out.println("I am father");
	}
	public Father(String name){
		System.out.println("I am father,My name is "+name);
	}
}
public class Child extends Father{
	public Child(){	
		super("Apache");
		System.out.println("I am child");
	}
	public static void main(String[] args) {
		Father f=new Father("Apache");
		Child c=new Child();
	}
}

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