java学习笔记day09

思维导图

final 、 多态 、 抽象类 、 接口（都很重要）

一、final

二、多态

多态中的成员访问特点⭐ 【P237】

多态的好处 【P239]

多态的弊端

向上转型、向下转型 ⭐【P241】

形象案例：孔子装爹

多态的问题理解：class 孔子爹 {public int age = 40;public void teach() {System.out.println("讲解JavaSE");}}class 孔子 extends 孔子爹 {public int age = 20;public void teach() {System.out.println("讲解论语");}public void playGame() {System.out.println("英雄联盟");}}//Java培训特别火,很多人来请孔子爹去讲课，这一天孔子爹被请走了//但是还有人来请，就剩孔子在家，价格还挺高。孔子一想，我是不是可以考虑去呢?//然后就穿上爹的衣服，带上爹的眼睛，粘上爹的胡子。就开始装爹//向上转型孔子爹 k爹 = new 孔子();//到人家那里去了System.out.println(k爹.age); //40k爹.teach(); //讲解论语//k爹.playGame(); //这是儿子才能做的//讲完了，下班回家了//脱下爹的装备，换上自己的装备//向下转型孔子 k = (孔子) k爹; System.out.println(k.age); //20k.teach(); //讲解论语k.playGame(); //英雄联盟

多态继承中的内存图解⭐⭐【P242】

多态中对象变化的内存图解 【P243】

多态的3道练习题【P245~P246】⭐

1.猫与狗

/*多态练习：猫狗案例*/class Animal {public void eat(){System.out.println("吃饭");}}class Dog extends Animal {public void eat() {System.out.println("狗吃肉");}public void lookDoor() {System.out.println("狗看门");}}class Cat extends Animal {public void eat() {System.out.println("猫吃鱼");}public void playGame() {System.out.println("猫捉迷藏");}}class DuoTaiTest {public static void main(String[] args) {//定义为狗Animal a = new Dog();a.eat();System.out.println("--------------");//还原成狗Dog d = (Dog)a;d.eat();d.lookDoor();System.out.println("--------------");//变成猫a = new Cat();a.eat();System.out.println("--------------");//还原成猫Cat c = (Cat)a;c.eat();c.playGame();System.out.println("--------------");//演示错误的内容//Dog dd = new Animal();//Dog ddd = new Cat();//ClassCastException//Dog dd = (Dog)a;}}

2.南方人与北方人

/*不同地方饮食文化不同的案例*/class Person {public void eat() {System.out.println("吃饭");}}class SouthPerson extends Person {public void eat() {System.out.println("炒菜,吃米饭");}public void jingShang() {System.out.println("经商");}}class NorthPerson extends Person {public void eat() {System.out.println("炖菜,吃馒头");}public void yanJiu() {System.out.println("研究");}}class DuoTaiTest2 {public static void main(String[] args) {//测试//南方人Person p = new SouthPerson();p.eat();System.out.println("-------------");SouthPerson sp = (SouthPerson)p;sp.eat();sp.jingShang();System.out.println("-------------");//北方人p = new NorthPerson();p.eat();System.out.println("-------------");NorthPerson np = (NorthPerson)p;np.eat();np.yanJiu();}}

3.我爱你（多层继承练习）⭐

/*看程序写结果:先判断有没有问题，如果没有，写出结果多态的成员访问特点：方法：编译看左边，运行看右边。继承的时候：子类中有和父类中一样的方法，叫重写。子类中没有父亲中出现过的方法，方法就被继承过来了。*/class A {public void show() {show2();}public void show2() {System.out.println("我");}}class B extends A {/*public void show() {show2();}*/public void show2() {System.out.println("爱");}}class C extends B {public void show() {super.show();}public void show2() {System.out.println("你");}}public class DuoTaiTest4 {public static void main(String[] args) {A a = new B();a.show();B b = new C();b.show();}}

三、抽象类

抽象类的成员特点

抽象类的案例

1.猫狗案例

//定义抽象的动物类abstract class Animal {//姓名private String name;//年龄private int age;public Animal() {}public Animal(String name,int age) {this.name = name;this.age = age;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}//定义一个抽象方法public abstract void eat();}//定义具体的狗类class Dog extends Animal {public Dog() {}public Dog(String name,int age) {super(name,age);}public void eat() {System.out.println("狗吃肉");}}//定义具体的猫类class Cat extends Animal {public Cat() {}public Cat(String name,int age) {super(name,age);}public void eat() {System.out.println("猫吃鱼");}}//测试类class AbstractTest {public static void main(String[] args) {//测试狗类//具体类用法//方式1：Dog d = new Dog();d.setName("旺财");d.setAge(3);System.out.println(d.getName()+"---"+d.getAge());d.eat();//方式2：Dog d2 = new Dog("旺财",3);System.out.println(d2.getName()+"---"+d2.getAge());d2.eat();System.out.println("---------------------------");Animal a = new Dog();a.setName("旺财");a.setAge(3);System.out.println(a.getName()+"---"+a.getAge());a.eat();Animal a2 = new Dog("旺财",3);System.out.println(a2.getName()+"---"+a2.getAge());a2.eat();//练习：测试猫类}}

2.老师案例

/*老师案例具体事物：基础班老师，就业班老师共性：姓名，年龄，讲课。分析：基础班老师姓名，年龄讲课。就业班老师姓名，年龄讲课。实现：老师类基础班老师就业班老师*///定义抽象的老师类abstract class Teacher {//姓名private String name;//年龄private int age;public Teacher() {}public Teacher(String name,int age) {this.name = name;this.age = age;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}//抽象方法public abstract void teach();}//基础班老师类class BasicTeacher extends Teacher {public BasicTeacher(){}public BasicTeacher(String name,int age) {super(name,age);}public void teach() {System.out.println("基础班老师讲解JavaSE");}}//就业班老师类class WorkTeacher extends Teacher {public WorkTeacher(){}public WorkTeacher(String name,int age) {super(name,age);}public void teach() {System.out.println("就业班老师讲解JavaEE");}}class AbstractTest2 {public static void main(String[] args) {//具体的类测试，自己玩//测试(多态)//基础班老师Teacher t = new BasicTeacher();t.setName("刘意");t.setAge(30);System.out.println(t.getName()+"---"+t.getAge());t.teach();System.out.println("--------------");t = new BasicTeacher("刘意",30);System.out.println(t.getName()+"---"+t.getAge());t.teach();System.out.println("--------------");//就业班老师t = new WorkTeacher();t.setName("林青霞");t.setAge(27);System.out.println(t.getName()+"---"+t.getAge());t.teach();System.out.println("--------------");t = new WorkTeacher("林青霞",27);System.out.println(t.getName()+"---"+t.getAge());t.teach();}}

3.学员案例

/*学生案例具体事务：基础班学员，就业班学员共性：姓名，年龄，班级，学习，吃饭分析：基础班学员成员变量：姓名，年龄，班级成员方法：学习，吃饭就业班学员成员变量：姓名，年龄，班级成员方法：学习，吃饭得到一个学员类。成员变量：姓名，年龄，班级成员方法：学习，吃饭实现：学员类基础班学员就业班学员*///定义抽象学员类abstract class Student {//姓名private String name;//年龄private int age;//班级private String grand;public Student() {}public Student(String name,int age,String grand) {this.name = name;this.age = age;this.grand = grand;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public String getGrand() {return grand;}public void setGrand(String grand) {this.grand = grand;}//学习public abstract void study();//吃饭public void eat() {System.out.println("学习累了,就该吃饭");}}//具体基础班学员类class BasicStudent extends Student {public BasicStudent() {}public BasicStudent(String name,int age,String grand) {super(name,age,grand);}public void study() {System.out.println("基础班学员学习的是JavaSE");}}//具体就业班学员类class WorkStudent extends Student {public WorkStudent() {}public WorkStudent(String name,int age,String grand) {super(name,age,grand);}public void study() {System.out.println("就业班学员学习的是JavaEE");}}class AbstractTest3 {public static void main(String[] args) {//我仅仅测试基础班学员//按照多态的方式测试Student s = new BasicStudent();s.setName("林青霞");s.setAge(27);s.setGrand("1111");System.out.println(s.getName()+"---"+s.getAge()+"---"+s.getGrand());s.study();s.eat();System.out.println("--------------");s = new BasicStudent("武鑫",48,"1111");System.out.println(s.getName()+"---"+s.getAge()+"---"+s.getGrand());s.study();s.eat();//就业班测试留给自己玩}}

4.员工案例

/*假如我们在开发一个系统时需要对员工类进行设计，员工包含3个属性：姓名、工号以及工资。经理也是员工，除了含有员工的属性外，另为还有一个奖金属性。请使用继承的思想设计出员工类和经理类。要求类中提供必要的方法进行属性访问。分析：普通员工类成员变量：姓名、工号以及工资。成员方法：工作经理类：成员变量：姓名、工号以及工资，奖金属性成员方法：工作实现：员工类：普通员工类：经理类：*///定义员工类abstract class Employee {//姓名、工号以及工资private String name;private String id;private int salary;public Employee() {}public Employee(String name,String id,int salary) {this.name = name;this.id = id;this.salary = salary;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getId() {return id;}public void setId(String id) {this.id = id;}public int getSalary() {return salary;}public void setSalary(int salary) {this.salary = salary;}//工作public abstract void work();}//普通员工类class Programmer extends Employee {public Programmer(){}public Programmer(String name,String id,int salary) {super(name,id,salary);}public void work() {System.out.println("按照需求写代码");}}//经理类class Manager extends Employee {//奖金private int money; //bonus 奖金public Manager(){}public Manager(String name,String id,int salary,int money) {super(name,id,salary);this.money = money;}public void work() {System.out.println("跟客户谈需求");}public int getMoney() {return money;}public void setMoney(int money) {this.money = money;}}class AbstractTest4 {public static void main(String[] args) {//测试普通员工Employee emp = new Programmer();emp.setName("林青霞");emp.setId("czbk001");emp.setSalary(18000);System.out.println(emp.getName()+"---"+emp.getId()+"---"+emp.getSalary());emp.work();System.out.println("-------------");emp = new Programmer("林青霞","czbk001",18000);System.out.println(emp.getName()+"---"+emp.getId()+"---"+emp.getSalary());emp.work();System.out.println("-------------");/*emp = new Manager();emp.setName("刘意");emp.setId("czbk002");emp.setSalary(8000);emp.setMoney(2000);*///由于子类有特有的内容，所以我们用子类来测试Manager m = new Manager();m.setName("刘意");m.setId("czbk002");m.setSalary(8000);m.setMoney(2000);System.out.println(m.getName()+"---"+m.getId()+"---"+m.getSalary()+"---"+m.getMoney());m.work();System.out.println("-------------");//通过构造方法赋值m = new Manager("刘意","czbk002",8000,2000);System.out.println(m.getName()+"---"+m.getId()+"---"+m.getSalary()+"---"+m.getMoney());m.work();}}

抽象类的几个小问题

四、接口

接口特点

接口成员特点⭐【P257】

类与类、类与接口、接口与接口的关系【P258】

抽象类与接口的区别⭐

接口的两个案例⭐⭐⭐

1.猫狗跳高案例

/*猫狗案例,加入跳高的额外功能分析：从具体到抽象猫：姓名,年龄吃饭，睡觉狗：姓名,年龄吃饭，睡觉由于有共性功能，所以，我们抽取出一个父类：动物：姓名,年龄吃饭();睡觉(){}猫：继承自动物狗：继承自动物跳高的额外功能是一个新的扩展功能，所以我们要定义一个接口接口：跳高部分猫：实现跳高部分狗：实现跳高实现；从抽象到具体使用：使用具体类*///定义跳高接口interface Jumpping {//跳高功能public abstract void jump();}//定义抽象类abstract class Animal {//姓名private String name;//年龄private int age;public Animal() {}public Animal(String name,int age) {this.name = name;this.age = age;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}//吃饭();public abstract void eat();//睡觉(){}public void sleep() {System.out.println("睡觉觉了");}}//具体猫类class Cat extends Animal {public Cat(){}public Cat(String name,int age) {super(name,age);}public void eat() {System.out.println("猫吃鱼");}}//具体狗类class Dog extends Animal {public Dog(){}public Dog(String name,int age) {super(name,age);}public void eat() {System.out.println("狗吃肉");}}//有跳高功能的猫class JumpCat extends Cat implements Jumpping {public JumpCat() {}public JumpCat(String name,int age) {super(name,age);}public void jump() {System.out.println("跳高猫");}}//有跳高功能的狗class JumpDog extends Dog implements Jumpping {public JumpDog() {}public JumpDog(String name,int age) {super(name,age);}public void jump() {System.out.println("跳高狗");}}class InterfaceTest {public static void main(String[] args) {//定义跳高猫并测试JumpCat jc = new JumpCat();jc.setName("哆啦A梦");jc.setAge(3);System.out.println(jc.getName()+"---"+jc.getAge());jc.eat();jc.sleep();jc.jump();System.out.println("-----------------");JumpCat jc2 = new JumpCat("加菲猫",2);System.out.println(jc2.getName()+"---"+jc2.getAge());jc2.eat();jc2.sleep();jc2.jump();//定义跳高狗并进行测试的事情自己完成。}}

2.老师学生抽烟案例

/*老师和学生案例,加入抽烟的额外功能分析：从具体到抽象老师：姓名，年龄，吃饭，睡觉学生：姓名，年龄，吃饭，睡觉由于有共性功能，我们提取出一个父类，人类。人类：姓名，年龄吃饭();睡觉(){}抽烟的额外功能不是人或者老师，或者学生一开始就应该具备的，所以，我们把它定义为接口抽烟接口。部分老师抽烟：实现抽烟接口部分学生抽烟：实现抽烟接口实现：从抽象到具体使用：具体*///定义抽烟接口interface Smoking {//抽烟的抽象方法public abstract void smoke();}//定义抽象人类abstract class Person {//姓名private String name;//年龄private int age;public Person() {}public Person(String name,int age) {this.name = name;this.age = age;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}//吃饭();public abstract void eat();//睡觉(){}public void sleep() {System.out.println("睡觉觉了");}}//具体老师类class Teacher extends Person {public Teacher() {}public Teacher(String name,int age) {super(name,age);}public void eat() {System.out.println("吃大白菜");}}//具体学生类class Student extends Person {public Student() {}public Student(String name,int age) {super(name,age);}public void eat() {System.out.println("吃红烧肉");}}//抽烟的老师class SmokingTeacher extends Teacher implements Smoking {public SmokingTeacher() {}public SmokingTeacher(String name,int age) {super(name,age);}public void smoke() {System.out.println("抽烟的老师");}}//抽烟的学生class SmokingStudent extends Student implements Smoking {public SmokingStudent() {}public SmokingStudent(String name,int age) {super(name,age);}public void smoke() {System.out.println("抽烟的学生");}}class InterfaceTest2 {public static void main(String[] args) {//测试学生SmokingStudent ss = new SmokingStudent();ss.setName("林青霞");ss.setAge(27);System.out.println(ss.getName()+"---"+ss.getAge());ss.eat();ss.sleep();ss.smoke();System.out.println("-------------------");SmokingStudent ss2 = new SmokingStudent("刘意",30);System.out.println(ss2.getName()+"---"+ss2.getAge());ss2.eat();ss2.sleep();ss2.smoke();//测试老师留给自己练习}}