父：

package JZZ;

public class Person {
public String name;
public int age;
public String sex;
public void study() {
	System.out.println("studying");
}
public void showAge() {
	System.out.println(name+"的年龄"+age);
}
public void addAge() {
	age+=2;
}
}

子：

package JZZ;

public class Student {
	public String name;
	public int age;
	
	public String getName() {
		return name;
	}
	public void setName(String name) {
		if(name.length()>15) {
			name = "JAZ";
		}
		this.name = name;
	}
	
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		if( age<1 || age >450) {
			age = 10;
		}
		this.age = age;
	}
	@Override
	public String toString() {
		return "Student [name=" + name + ", age=" + age + "]";
	}
}

第一个Text.java：

package JZZ;

public class Text {
	
	public static void main(String[] age) {
		Person p1 = new Person();
		p1.name = "YMY";
		p1.age = 18;
		p1.sex = "女";
		p1.study();
		p1.showAge();
		p1.addAge();
		p1.showAge();
		System.out.println();
		Person p2 = new Person();
		p2.name = "JAZ";
		p2.age = 18;
		p2.sex = "男";
		p2.study();
		p2.showAge();
		p2.addAge();
		p2.showAge();
		
	}
}

测试结果：
studying
YMY的年龄18
YMY的年龄20

studying
JAZ的年龄18
JAZ的年龄20

第二个Textt.java：

package JZZ;

public class Textt {
	public static void main(String[] args) {
		Student s1 = new Student();
		s1.setName("YMY");
		s1.setAge(-18);
		
		String info =s1.toString();
		System.out.println(info);
	}
}

测试结果：
Student [name=YMY, age=10]