1. 多态数组 数组的定义类型为父类类型，里面保存的实际元素类型为子类类型 1.1 应用实例: 315 现有一个继承结构如下：要求创建 1 个 Person 对象、2 个 Student 对象和 2 个 Teacher 对象, 统
1. 多态数组
数组的定义类型为父类类型，里面保存的实际元素类型为子类类型
1.1 应用实例: 315
现有一个继承结构如下：要求创建 1 个 Person 对象、2 个 Student 对象和 2 个 Teacher 对象, 统一放在数组 中，并调用每个对象say 方法.
代码在com.stulzl.poly_array.包中
测试PloyArray
package com.stulzl.poly_array;
//多态数组 315
//现有一个继承结构如下：要求创建 1 个 Person 对象、2 个 Student 对象和 2 个 Teacher 对象,
// 统一放在数组 中，并调用每个对象say 方法.
public class PloyArray {
public static void main(String[] args) {
Person persons[] = new Person[5];//多态数组
persons[0]=new Person("jack",20);
persons[1]=new Student("jack",18,100);
persons[2]=new Student("smith",19,30);
persons[3]=new Teacher("july",30,20000);
persons[4]=new Teacher("king",50,25000);
//循环遍历数组
for (int i = 0; i < persons.length; i++) {
//person[i] 编译类型是 Person ,运行类型是是根据实际情况有 JVM 来判断
System.out.println(persons[i].say());//有动态绑定机制
}
}
}父类Person
package com.stulzl.poly_array;
public class Person {//父类
private String name;
private int age;
//构造器
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;
}
//返回信息
public String say(){
return name+"\t"+age;
}
}子类Student
package com.stulzl.poly_array;
public class Student extends Person{//子类
private double score;
public Student(String name, int age, double score) {
super(name, age);
this.score = score;
}
public double getScore() {
return score;
}
public void setScore(double score) {
this.score = score;
}
//返回信息
public String say(){
return "学生 "+super.say()+" "+score;
}
}子类Teacher
package com.stulzl.poly_array;
public class Teacher extends Person{//子类
private double salary;
public Teacher(String name, int age, double salary) {
super(name, age);
this.salary = salary;
}
public double getSalary() {
return salary;
}
public void setSalary(double salary) {
this.salary = salary;
}
//返回信息
public String say(){
return "老师 "+super.say()+" "+salary;
}
}1.2应用实例升级：316
如何调用子类特有的方法，比如 Teacher 有一个 teach , Student 有一个 study 怎么调用？
代码在com.stulzl.poly_array_pro.包中
测试PloyArray
package com.stulzl.poly_array_pro;
public class PolyArray {
public static void main(String[] args) {
Person persons[] = new Person[5];//多态数组
persons[0]=new Person("jack",20);
persons[1]=new Student("marry",18,100);
persons[2]=new Student("smith",19,30);
persons[3]=new Teacher("july",30,20000);
persons[4]=new Teacher("king",50,25000);
//循环遍历数组
for (int i = 0; i < persons.length; i++) {
//person[i] 编译类型是 Person ,运行类型是是根据实际情况有 JVM 来判断
System.out.println(persons[i].say());//有动态绑定机制
if(persons[i] instanceof Student){//判断person[i]的运行类型是不是Student
Student student = (Student)persons[1];//向下转型
student.study();
}else if(persons[i] instanceof Teacher){
Teacher teacher = (Teacher)persons[i];
teacher.teach();
}else if(persons[i] instanceof Person) {
}else{
System.out.println("您的运行类型有误");
}
}
}
}父类Person
package com.stulzl.poly_array_pro;
public class Person {//父类
private String name;
private int age;
//构造器
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;
}
//返回信息
public String say() {
return name + "\t" + age;
}
}子类Student
package com.stulzl.poly_array_pro;
public class Student extends Person {//子类
private double score;
public Student(String name, int age, double score) {
super(name, age);
this.score = score;
}
public double getScore() {
return score;
}
public void setScore(double score) {
this.score = score;
}
//返回信息
public String say(){
return "学生 "+super.say()+" "+score;
}
//特有方法
public void study(){
System.out.println("学生 "+getName()+" 正在学java课程");
}
}子类Teacher
package com.stulzl.poly_array_pro;
public class Teacher extends Person {//子类
private double salary;
public Teacher(String name, int age, double salary) {
super(name, age);
this.salary = salary;
}
public double getSalary() {
return salary;
}
public void setSalary(double salary) {
this.salary = salary;
}
//返回信息
public String say(){
return "老师 "+super.say()+" "+salary;
}
//特有方法
public void teach(){
System.out.println("老师 "+getName()+" 正在讲java课程");
}
}2. 多态参数 317
方法定义的形参类型为父类类型，实参类型允许为子类类型
2.1 例 317
代码在com.stulzl.poly_parameter.包中
测试PolyParameter
package com.stulzl.poly_parameter;
//多态参数 317
public class PolyParameter {
public static void main(String[] args) {
Worker tom = new Worker("tom",2500);
Manager milan = new Manager("milan",5000,200000);
//这里是声明对象调用本类方法
PolyParameter polyParameter = new PolyParameter();
polyParameter.showEmpAnnual(tom);
polyParameter.testWork(tom);
polyParameter.showEmpAnnual(milan);
polyParameter.testWork(milan);
}
//showEmpAnnual(Employee e)
//实现获取任何员工对象的年工资,并在 main 方法中调用该方法 [e.getAnnual()]
public void showEmpAnnual(Employee e){//使用父类接收，编译类型父类Employee，运行类型具体看子类
System.out.println(e.getAnnual());//这里涉及动态绑定机制
}
//添加一个方法，testWork,如果是普通员工，则调用 work 方法，如果是经理，则调用 manage 方法
public void testWork(Employee e){//还是编译类型父类Employee，运行类型具体看子类
if(e instanceof Worker){//判断e的运行类型是不是Worker的类型
Worker worker = (Worker)e;//向下强转
worker.work();
}else if(e instanceof Manager){
Manager manager = (Manager)e;
manager.manager();
}else{
System.out.println("不做处理");
}
}
}父类Employee
package com.stulzl.poly_parameter;
public class Employee {//父类
private String name;
private double salary;
public Employee(String name, double salary) {
this.name = name;
this.salary = salary;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public double getSalary() {
return salary;
}
public void setSalary(double salary) {
this.salary = salary;
}
//返回年度总工资
public double getAnnual(){
return 12*salary;
}
}子类Worker
package com.stulzl.poly_parameter;
public class Worker extends Employee {//子类
public Worker(String name, double salary) {
super(name, salary);
}
//特有的工作方法
public void work(){
System.out.println("普通员工 "+getName()+" 在工作");
}
//重写获取年薪的方法，因为普通员工没有其他收入，则直接调用父类方法getAnnual()
public double getAnnual() {
return super.getAnnual();
}
}子类Manager
package com.stulzl.poly_parameter;
public class Manager extends Employee {//子类
private double bonus;
public Manager(String name, double salary, double bonus) {
super(name, salary);
this.bonus = bonus;
}
public double getBonus() {
return bonus;
}
public void setBonus(double bonus) {
this.bonus = bonus;
}
//经理特有的管理方法
public void manager(){
System.out.println("经理 "+getName()+" 正在管理");
}
//重写获取年薪的方法
public double getAnnual(){
return super.getAnnual()+bonus;
}
}