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abstract：

1、用来修饰类，此类被称为抽象类。且此类不能够实例化，包含构造器的，因为子类对象实例化时，需要调用父类的构造器。可以没有抽象方法。

2、此方法称为抽象方法，此方法只有方法的声明，没有方法体。

其功能是确定的，通过方法的声明来确定，只是不知道功能如何实现（体现为方法体）

子类必须重写父类所有方法，方可实例化。否则仍是抽象类。

abstract不能修饰私有方法、static方法、final方法、final类

*私有方法不能重写，abstract则必须重写

*静态方法允许调用，而abstract的父类方法不能调用

*final方法不能重写，abstract则必须重写

*final类不能有子类，abstract有子类

例题：

Employee类：

public abstract class Employee {private String name;private int number;private Mydate birthday;public Employee() {}public Employee(String name, int number, Mydate birthday) {this.name = name;this.number = number;this.birthday = birthday;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getNumber() {return number;}public void setNumber(int number) {this.number = number;}public Mydate getBirthday() {return birthday;}public void setBirthday(Mydate birthday) {this.birthday = birthday;}public abstract double earning();public String toString(){return "姓名,"+name+"数字,"+number+"生日"+birthday.toDateString();}
}

Mydate类：

public class Mydate {private int year;private int month;private int day;public Mydate() {}public Mydate(int year, int month, int day) {this.year = year;this.month = month;this.day = day;}public int getYear() {return year;}public void setYear(int year) {this.year = year;}public int getMonth() {return month;}public void setMonth(int month) {this.month = month;}public int getDay() {return day;}public void setDay(int day) {this.day = day;}public String toDateString(){return year+"年"+month+"月"+day+"日";}
}

SalariedEmployee类：

public class SalariedEmployee extends Employee{private double monthlySalary;public SalariedEmployee() {}public SalariedEmployee(String name, int number, Mydate birthday, double monthlySalary) {super(name, number, birthday);this.monthlySalary = monthlySalary;}public void setMonthlySalary(double monthlySalary) {this.monthlySalary = monthlySalary;}public double earning(){return monthlySalary;}public String toString(){return "SalariedEmployee[" + super.toString()+"]";}}

HourlyEmployee类：

public  class HourlyEmployee extends Employee {private double wage;private int hour;public HourlyEmployee() {}public HourlyEmployee(String name, int number, Mydate birthday, double wage, int hour) {super(name, number, birthday);this.wage = wage;this.hour = hour;}public double getWage() {return wage;}public void setWage(double wage) {this.wage = wage;}public int getHour() {return hour;}public void setHour(int hour) {this.hour = hour;}public  double earning(){return wage*hour;}public String toString(){return "HourlyEmployee[" + super.toString()+"]";}
}

PayrollSystem类：

import java.util.Scanner;public class PayrollSystem {public static void main(String[] args) {Scanner scanner=new Scanner(System.in);Employee[] e=new Employee[2];e[0]=new SalariedEmployee("马国森", 123, new Mydate(2001, 1, 1),5000);e[1]=new HourlyEmployee("王悦",123,new Mydate(2001,2,2),32,5);System.out.println("请输入月份");int input=scanner.nextInt();for (int i = 0; i < e.length; i++) {System.out.println(e[i].toString());System.out.println("工资:"+e[i].earning());if (input == e[i].getBirthday().getMonth()) {System.out.println("生日快乐，加薪200！");}}scanner.close();}}