//在包person下
//Person.java
package person;public class Person {    public Person(String name, int age) {super();this.name = name;this.age = age;}protected String name;protected int age;public String getInfo() {return "姓名："+name+"，年龄："+age+" ";}
}//Student.java
package person;public class Student extends Person {protected String school;protected String grade;Student(String name,int age,String school,String grade){super(name,age);this.school=school;this.grade=grade;}public String getInfo() {return super.getInfo()+"学校：" +school+" ,年级："+grade;}
}//Demo.java
package person;public class Demo {public static void main(String[] args) {// TODO Auto-generated method stubPerson person =new Person("小张",18);System.out.println(person.getInfo());Student student=new Student("小李",20,"天津大学","大一");System.out.println(student.getInfo());}}

package finaldemo;public class Demo {public final double PI=3.14;public final int[] arr= {1,2,3};public final String str = "Welcome to Java";public static void main(String[] args) {// TODO Auto-generated method stubDemo demo = new Demo();demo.PI=3.14159;               //errordemo.arr=new int[5];           //errordemo.arr[2]=4;                 //rightdemo.str="that's a error!";    //error
        System.out.println(demo.PI);for(int i=0;i<3;i++) {System.out.print(demo.arr[i]+" ");}System.out.println();System.out.println(demo.str);}}

//package Demo2 下
//Animal.java
package Demo2;public class Animal {public Animal(String name) {super();this.name = name;}String name;}//Cat.java
package Demo2;public class Cat extends Animal {String eyeColor;public Cat(String name,String eyeColor) {super(name);// TODO Auto-generated constructor stubthis.eyeColor=eyeColor;}}//Dog.java
package Demo2;public class Dog extends Animal {String furColor;public Dog(String name,String furColor) {super(name);// TODO Auto-generated constructor stubthis.furColor=furColor;}}//Demo.java
package Demo2;public class Demo {public static void main(String[] args) {// TODO Auto-generated method stubAnimal animal = new Animal("animal");Cat cat =new Cat("cat","blue");Dog dog = new Dog("dog","black");//判断animal，cat，dog是否为AnimalSystem.out.println("animal is Animal? "+ (animal instanceof Animal));System.out.println("cat is Animal? "+ (cat instanceof Animal));System.out.println("dog is Animal? "+ (dog instanceof Animal));animal=dog;System.out.println(animal.name);System.out.println("animal is Dog? "+ (animal instanceof Dog));}}