多态的应用
多态数组
应用实例:现有一个继承结构如下,要求创建1个Person对象,2个Student对象,2个Teacher对象,统一放在数组中,并调用每个对象say方法.
public class Person {//父类
private String name;
private int age;
public Person(String name, int age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public int getAge() {
return age;
}
public void setName(String name) {
this.name = name;
}
public void setAge(int age) {
this.age = age;
}
public String say (){
return name + "\t" + age;
}
}
public class Student extends Person{//学生类
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;
}
@Override
public String say() {
return "学生:"+super.say() + " score= " + score;
}
}
public class Teacher extends Person{//老师类
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;
}
@Override
public String say() {
return "老师:"+super.say()+" salary= " + salary;
}
}
public class PolyArray {//main方法
public static void main(String[] args) {
Person[] person = new Person[5];
person[0] = new Person("dawei",25);
person[1] = new Student("erwei",23,60);
person[2] = new Student("sanwei",22,70);
person[3] = new Teacher("dazou",27,10000);
person[4] = new Teacher("erzou",25,20000);
for (int i = 0; i < 5; i++) {
//person编译类型是Person,运行类型根据实际情况由JVM来判断
System.out.println(person[i].say());//动态绑定机制
}
}
}
应用实例升级: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?
- 先分别在S和T两个类里添加study和teach方法
- 此时在main方法里继续用person调用teach和study是会报错的,因为编译类型是person,而person类里没有子类特有的方法.此时的解决办法可以是通过
instanceof
来进行判断运行类型并向下转型.再执行对于的方法.
多态参数
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
应用实例1:前面的主人喂动物
应用实例2: com.happywei.poly .polyparameter 包 PloyParameter.java定义员工类Employee,包含姓名和月工资[private],以及计算年工资getAnnual的方法。普通员工和经理继承了员工,经理类多了奖金bonus属性和管理manage方法,普通员工类多了work方法,普通员工和经理类要求分别重写getAnnual方法
测试类中添加一个方法showEmpAnnal(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()]
测试类中添加一个方法,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