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1.什么是封装,如何使用封装
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package case1;
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public class TestPersonDemo {
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public static void main(String[] args) {
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/********* begin *********/
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// 声明并实例化一Person对象p
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Person p = new Person();
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// 给p中的属性赋值
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p.setName("张三");
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p.setAge("18岁");
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// 调用Person类中的talk()方法
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p.talk();
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/********* end *********/
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}
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}
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// 在这里定义Person类
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class Person {
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/********* begin *********/
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private String name;
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private String age;
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public String getName(){
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return name;
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}
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public void setName(String name){
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this.name = name;
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}
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public String getAge(){
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return age;
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}
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public void setAge(String age){
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this.age = age;
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}
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public void talk(){
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System.out.print("我是:"+name+",今年:"+age);
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}
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/********* end *********/
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}
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2.什么是继承,怎样使用继承
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package case2;
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public class extendsTest {
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public static void main(String args[]) {
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// 实例化一个Cat对象,设置属性name和age,调用voice()和eat()方法,再打印出名字和年龄信息
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/********* begin *********/
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Cat c=new Cat("大花猫",6);
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c.voice("大花猫");
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c.eat("大花猫");
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System.out.println(c.getName()+c.getAge()+"岁");
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/********* end *********/
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// 实例化一个Dog对象,设置属性name和age,调用voice()和eat()方法,再打印出名字和年龄信息
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/********* begin *********/
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Dog d=new Dog("大黑狗",8);
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d.voice("大黑狗");
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d.eat("大黑狗");
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System.out.println(d.getName()+d.getAge()+"岁");
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/********* end *********/
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}
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}
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class Animal {
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/********* begin *********/
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private String name;
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private int age;
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public Animal(String name,int age){
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this.name = name;
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this.age =age;
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}
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public String getName(){
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return name;
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}
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public void setName(String name){
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this.name=name;
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}
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public int getAge(){
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return age;
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}
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public void setAge(int age){
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this.age = age;
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}
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/********* end *********/
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}
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class Cat extends Animal {
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// 定义Cat类的voice()和eat()方法
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/********* begin *********/
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public Cat(String name,int age){
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super(name,age);
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}
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public void voice(String name){
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System.out.println(name+"喵喵叫");
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}
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public void eat(String name){
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System.out.println(name+"吃鱼");
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}
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/********* end *********/
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}
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class Dog extends Animal {
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// 定义Dog类的voice()和eat()方法
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/********* begin *********/
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public Dog(String name,int age){
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super(name,age);
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}
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public void voice(String name){
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System.out.println(name+"汪汪叫");
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}
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public void eat(String name){
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System.out.println(name+"吃骨头");
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}
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/********* end *********/
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}
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3.方法的重写与重载
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package case4;
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public class overridingTest {
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public static void main(String[] args) {
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// 实例化子类对象s,调用talk()方法打印信息
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/********* begin *********/
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Student s=new Student("张三",18,"哈佛大学");
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s.talk();
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/********* end *********/
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}
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}
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class Person {
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/********* begin *********/
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String name;
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int age;
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public void talk(){
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System.out.println("我是:"+name+"今年:"+age+"岁");
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}
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/********* end *********/
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}
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class Student extends Person {
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/********* begin *********/
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String school;
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Student(String name,int age,String school){
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this.name=name;
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this.age=age;
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this.school=school;
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}
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public void talk(){
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System.out.print("我是:"+name+","+"今年:"+age+"岁"+","+"我在"+school+"上学");
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}
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/********* end *********/
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}
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4.抽象类
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package case5;
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public class abstractTest {
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public static void main(String[] args) {
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/********* begin *********/
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// 分别实例化Student类与Worker类的对象,并调用各自构造方法初始化类属性。
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Student s=new Student("张三",20,"学生");
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Worker w=new Worker("李四",30,"工人");
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// 分别调用各自类中被复写的talk()方 印息
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s.talk();
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w.talk();
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/********* end *********/
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}
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}
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// 声明一个名为Person的抽象类,在Person中声明了三个属性name age occupation和一个抽象方法——talk()。
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abstract class Person {
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/********* begin *********/
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String name;
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int age;
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String occupation;
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abstract void talk();
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/********* end *********/
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}
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// Student类继承自Person类,添加带三个参数的构造方法,复写talk()方法 返回姓名、年龄和职业信息
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class Student extends Person {
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/********* begin *********/
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public Student(String name,int age,String occupation){
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this.name=name;
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this.age=age;
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this.occupation=occupation;
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}
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public void talk(){
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System.out.println("学生——>姓名:"+this.name+","+"年龄:"+this.age+","+"职业:"+this.occupation+"!");
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}
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/********* end *********/
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}
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// Worker类继承自Person类,添加带三个参数的构造方法,复写talk()方法 返回姓名、年龄和职业信息
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class Worker extends Person {
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/********* begin *********/
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public Worker(String name,int age,String occupation){
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this.name=name;
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this.age=age;
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this.occupation=occupation;
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}
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public void talk(){
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System.out.println("工人——>姓名:"+this.name+","+"年龄:"+this.age+","+"职业:"+this.occupation+"!");
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}
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/********* end *********/
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}
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5.接口
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package case7;
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public class interfaceTest {
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public static void main(String[] args) {
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// 实例化一Student的对象s,并调用talk()方法,打印信息
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/********* begin *********/
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Student s=new Student();
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System.out.println(s.talk());
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/********* end *********/
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}
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}
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// 声明一个Person接口,并在里面声明三个常量:name、age和occupation,并分别赋值,声明一抽象方法talk()
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interface Person {
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/********* begin *********/
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final String name="张三";
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final int age=18;
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final String occupation="学生";
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abstract String talk();
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/********* end *********/
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}
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// Student类继承自Person类 复写talk()方法返回姓名、年龄和职业信息
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class Student implements Person {
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/********* begin *********/
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public String talk(){
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return "学生——>姓名:"+this.name+","+"年龄:"+this.age+","+"职业:"+this.occupation+"!";
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}
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/********* end *********/
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}
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6.super关键字的使用
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package case3;
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public class superTest {
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public static void main(String[] args) {
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// 实例化一个Student类的对象s,为Student对象s中的school赋值,打印输出信息
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/********* begin *********/
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Student s = new Student();
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s.school = "哈佛大学";
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System.out.println("姓名:"+s.name+",年龄:"+s.age+",学校:"+s.school);
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/********* end *********/
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}
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}
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class Person {
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/********* begin *********/
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String name;
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int age;
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public Person(String name,int age){
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this.name=name;
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this.age=age;
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}
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/********* end *********/
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}
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class Student extends Person {
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/********* begin *********/
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String school;
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public Student(){
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super("张三",18); //super调用父类的方法
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}
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/********* end *********/
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}
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7.final关键字的理解与使用
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package case6;
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public class finalTest {
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public static void main(String args[]) {
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Bike1 obj = new Bike1();
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obj.run();
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Honda honda = new Honda();
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honda.run();
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Yamaha yamaha = new Yamaha();
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yamaha.run();
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}
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}
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//不可以修改 final 变量的值
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// final方法,不可以重写
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//不可以扩展 final 类
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//请在此添加你的代码
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/********** Begin *********/
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class Bike1 {
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int speedlimit = 90;
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void run() {
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speedlimit = 120;
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System.out.println("speedlimit=120");
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}
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}
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class Bike2 {
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void run() {
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System.out.println("running");
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}
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}
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class Honda extends Bike2 {
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void run() {
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System.out.println("running safely with 100kmph");
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}
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}
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class Bike3 {
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}
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class Yamaha extends Bike3 {
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void run() {
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System.out.println("running safely with 100kmph");
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}
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}
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/********** End **********/
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8.什么是多态,怎么使用多态
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package case8;
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public class TestPolymorphism {
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public static void main(String[] args) {
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// 以多态方式分别实例化子类对象并调用eat()方法
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/********* begin *********/
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Animal dog=new Dog();
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dog.eat();
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Animal cat=new Cat();
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cat.eat();
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Animal lion=new Lion();
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lion.eat();
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/********* end *********/
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}
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}
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// Animal类中定义eat()方法
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class Animal {
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/********* begin *********/
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public void eat(){
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}
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/********* end *********/
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}
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// Dog类继承Animal类 复写eat()方法
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class Dog extends Animal {
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/********* begin *********/
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public void eat(){
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System.out.println("eating bread...");
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}
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/********* end *********/
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}
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// Cat类继承Animal类 复写eat()方法
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class Cat extends Animal {
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|
/********* begin *********/
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|
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|
|
public void eat(){
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|
|
System.out.println("eating rat...");
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}
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|
|
/********* end *********/
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|
|
|
|
}
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// Lion类继承Animal类 复写eat()方法
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|
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class Lion extends Animal {
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|
|
/********* begin *********/
|
|
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|
|
public void eat(){
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|
|
|
|
System.out.println("eating meat...");
|
|
|
|
|
}
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|
|
/********* end *********/
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|
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|
|
}
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