java初学--class extends

Person.java

public class Person { int age; String name; String school; Person(String name,int age) { this.name=name; this.age=age; } Person(String string, int age, String school) { this.name=name; this.age=age; this.school=school; } void sayHello(Student s) { System.out.println("My school is "+school); } void sayHello() { System.out.println("wpx"); } } Student.java

public class Student extends Person { String school; int score; void sayHello(Student another) { System.out.println("Hi!"); if(school==another.school ) System.out.println(" Shoolmates"); } boolean isGoodStudent() { return score>=90; } void testThisSuper() { int a; a=age; a=this.age; a=super.age; } void sayHello() { super.sayHello(); System.out.println("My school is "+school); } Student(String name,int age,String school) { super(name,age); this.school=school; } // Student()(); public static void main(String []args) { Person p=new Person("Liming",50); Student s=new Student("Wangqiang",20,"PKU"); Person p2=new Student("Zhangyi",18,"THU"); // Student s2=(Student)p2;//强制转换 // Student s3=(Student)p; p.sayHello(s); Person []manypeople = new Person[100]; manypeople[0] = new Person("Li",18); manypeople[1] = new Person("Wang",18,"PKU"); } }