package pkg;

class Student{
	private String name;
	Student(String name){
		this.name=name;
	}
	protected void set(String nm) {
		name=nm;
	}
	protected void change() {
		name="Jack";
	}
	public String toString() {
	//must be PUBLIC:Cannot reduce the visibility of the inherited method from Object
		return "My name is "+name;
	}
}

public class p138 extends Student{
	p138(String name){
		super(name);
	}
	
	void change(String name) {
		set(name);
		//super.set(name);// is also OK
	}
	
	void defaultSet() {
		change();//don't need to be invoked by one OBJECT
	}
	
	public String toString() {
		return "My name is "+super.toString();
	}
	
	
	public static void main(String[] args) {
		p138 obj=new p138("Alice");
		System.out.println(obj);
		obj.change("Bob");
		System.out.println(obj);
		obj.defaultSet();
		System.out.println(obj);

	}
}

OUTPUT:

My name is My name is Alice
My name is My name is Bob
My name is My name is Jack

总结：

1、toString()函数是Object的遗传方法，必须定义为public；

2、protected可以被其它包中的子类来访问。

3、子类中可以直接调用基类中的方法，而不必生成具体的对象。