有道难题

class Base {
	private String name = "base";

	public Base(){
		tellName();
		printName(name);
	}
	public void tellName(){
		System.out.println("Base tell name: "+ name);
	}
	public void printName(String name) {
		System.out.println("Base print name: "+name);
	}
}

public class Derived extends Base {
	private String name = "derived";

	public Derived() {
		tellName();
		printName(name);
	}

	public void tellName() {
		System.out.println("Derived tell name: " +name);
	}

	public void printName(String name) {
		System.out.println("Derived print name: " + name);
	}
	public static void main(String args[]) {
		new Derived();
		
	}
}

输出结果：

Derived tell name: null
Derived print name: base
Derived tell name: derived
Derived print name: derived

思路：在new Derived()的构造器里面，先调用了super（此时Derived的name还没有初始化），然后new Base()（省略super初始化Object了部分），其中的tellName被重写了，所以调用子类的tellName;然后再去执行被重写的printName；然后去初始化Derived的name……

printName

printName