JAVA动态绑定机制（非常非常重要）

JAVA动态绑定机制：动态绑定是与运行类型进行绑定

1.当调用对象方法的时候，该方法会和该对象的内存地址/运行类型（也就是与运行类型）绑定（意思就是如：有一个Cat类，Cat类中有一个cay方法，这个方法会和Cat类发生动态绑定）

2.当调用对象属性时，没有动态绑定机制，哪里声明，哪里使用

package JAVA面向对象中级部分.encapsulationAndInherit.binding;public class DynamicBinding {public static void main(String[] args) {A a  = new B();//向上转型//当注释了B类中的sum()方法和sum1()方法结果变为了30和20System.out.println(a.sum());//40 --》30System.out.println(a.sum1());//30 --》20}
}class A{//父类public int i = 10;//由于调用方法时，方法会和该对象的内存地址（也就是运行类型）绑定//由于运行类型是B，所以查找是从B类方法开始查找，要因为B类中的getI()方法，直接返回属性i,属性没有动态绑定机制，因此直接返回20public int sum(){return getI()+10;}//方法是有动态绑定机制，所以查找时，先从子类B查找，由于B类没有sum1方法，//继承查找父类，父类有则调用sum1方法，要因为sum1方法返回是属性i，属性没有动态绑定机制直接返回i的值，所以是20public int sum1(){return i+10;}public int getI(){return i;}
}class B extends A {public int i = 20;
//    public int sum(){
//        return i+20;
//    }
//
//    public int sum1(){
//        return i+10;
//    }public int getI(){return i;}
}

多态应用

基本介绍：多态数组是数组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

案例：

1.现有一个继承结构如下：要求创建一个Person对象，2个Student对象和2个Teacher对象，统一放在数组中。并调用msay方法。
2.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？

package JAVA面向对象中级部分.encapsulationAndInherit.ployArray;public class Person {private String name;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;}public String say(){return "姓名:"+name+"\t年龄:"+age;}}package JAVA面向对象中级部分.encapsulationAndInherit.ployArray;public class Student extends  Person{private double score;public Student(String name,int age) {this.setName(name);this.setAge(age);}public Student(String name,int age,double score){//注意在构造器中使用super和this调用构造器完成初始化，两者只能出一个并且放在第一条语句super(name,age);
//        this(name,age);this.score =score;}public String say(){return super.say()+"\t成绩:"+score;}public void study(){System.out.println("学生:"+getName()+"正在学习JAVA课程！");}
}
package JAVA面向对象中级部分.encapsulationAndInherit.ployArray;public class Teacher extends  Person{private double salary;public Teacher(String name,int  age) {this.setName(name);this.setAge(age);}public Teacher(String name,int age,double salary){super(name,age);this.salary = salary;}public String say(){return super.say()+"\tsalary:"+salary;}public void teach(){System.out.println("老师:"+getName()+"正在教JAVA课程！");}
}package JAVA面向对象中级部分.encapsulationAndInherit.ployArray;public class PloyArray {public static void main(String[] args) {Person[] people = new Person[5];people[0] = new Person("海康",20);people[1] = new Student("湛江",18,99);people[2] = new Student("南宁",20,99.9);people[3] = new Teacher("西安",21,21688);people[4] = new Teacher("广州",22,22168);//循环遍历多态数组，调用sayfor (int i = 0; i < people.length; i++) {//person[i]编译类型是Person，运行类型是根据实际情况有JV来判断
//            System.out.println(people[i].say());//动态绑定机制if (people[i] instanceof Student){Student student = (Student) people[i];student.study();}else if (people[i] instanceof  Teacher){Teacher teacher = (Teacher) people[i];teacher.teach();}else {System.out.println(people[i].say());//在类型转换时，范围大的一定要放在后面，要不大的对小范围有接收作用}}}
}

多态参数问题

基本介绍：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：

定义员工类Employee，包含姓名和月工资【prvate】，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 employee)，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【employee.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package JAVA面向对象中级部分.encapsulationAndInherit.ployParameter;public class PloyParameter {public static void main(String[] args) {Worker worker = new Worker("海康", 18168);testWork(worker);double v = showEmpAnnual(worker);System.out.println(v);System.out.println("=================经理===============");Manager manager = new Manager("明天", 81688, 100000);testWork(manager);double v1 = showEmpAnnual(manager);System.out.println(v1);}public static double showEmpAnnual(Employee employee){return employee.getAnnual();}public static void testWork(Employee employee){if (employee instanceof Worker){Worker worker = (Worker) employee;worker.work();}else if (employee instanceof Manager){Manager manager = (Manager) employee;manager.manage();}else {System.out.println("您输入的类型有误！");}}
}
package JAVA面向对象中级部分.encapsulationAndInherit.ployParameter;public class Employee {private String name;private double salary;public Employee() {}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;}//计算年工资getAnnual方法public double getAnnual(){return salary*12;}
}
package JAVA面向对象中级部分.encapsulationAndInherit.ployParameter;public class Worker  extends Employee{public Worker() {}public Worker(String name, double salary) {super(name, salary);}//普通员工work方法public void work(){System.out.println("普通员工打工干活");}public double getAnnual(){return getSalary()*12;}
}
package JAVA面向对象中级部分.encapsulationAndInherit.ployParameter;public class Manager extends Employee{private double bonus;public Manager(String name,double salary){super(name,salary);}public Manager(double bonus) {this.bonus = bonus;}public Manager(String name, double salary, double bonus) {super(name, salary);this.bonus = bonus;}//管理方法public void manage(){System.out.println("经理放屁了");}public double getAnnual(){return getSalary()*12 + bonus;}
}