1 package org.mano.example;
  2 public class Company
  3 {
  4    public static void main( String[] args )
  5    {
  6       Payroll payroll = new Payroll();
  7       payroll.paySalary();
  8    }
  9 }
 10 package org.mano.example;
 11 import java.util.ArrayList;
 12 import java.util.List;
 13 public class Payroll {
 14    private List<Employee> employees =
 15       new ArrayList<>();
 16    public Payroll() {
 17       employees.add(new
 18             SalariedEmployee("Harry Potter",
 19          "123-234-345",7800));
 20       employees.add(new
 21             CommissionEmployee("Peter Parker",
 22          "234-345-456",2345.67,0.15));
 23       employees.add(new
 24             HourlyEmployee("Joker Poker",
 25          "456-567-678",562.36,239.88));
 26    }
 27    public void paySalary() {
 28       for (Employee e: employees) {
 29          System.out.println
 30             ("----------------------------------------------------");
 31          System.out.println(e.toString());
 32          System.out.printf
 33             ("Gross payment: $%,.2f\n",e.salary());
 34          System.out.println
 35             ("----------------------------------------------------");
 36       }
 37    }
 38 }
 39  
 40 package org.mano.example;
 41  
 42 public abstract class Employee {
 43    protected String name;
 44    protected String ssn;
 45    public Employee(String name, String ssn) {
 46       this.name = name;
 47       this.ssn = ssn;
 48    }
 49    public String getName() {
 50       return name;
 51    }
 52    public void setName(String name) {
 53       this.name = name;
 54    }
 55    public String getSsn() {
 56       return ssn;
 57    }
 58    public void setSsn(String ssn) {
 59       this.ssn = ssn;
 60    }
 61    @Override
 62    public String toString() {
 63       return String.format("%s\nSSN: %s",
 64          getName(),getSsn());
 65    }
 66    public abstract double salary();
 67 }
 68  
 69 package org.mano.example;
 70 public class SalariedEmployee extends Employee {
 71    protected double basicSalary;
 72    public SalariedEmployee(String name, String ssn,
 73          double basicSalary) {
 74       super(name, ssn);
 75       setBasicSalary(basicSalary);
 76    }
 77    public double getBasicSalary() {
 78       return basicSalary;
 79    }
 80    public void setBasicSalary(double basicSalary) {
 81       if(basicSalary>= 0.0)
 82          this.basicSalary = basicSalary;
 83       else
 84          throw new IllegalArgumentException("basic " +
 85             "salary must be greater than 0.0");
 86    }
 87    @Override
 88    public double salary() {
 89       eturn getBasicSalary();
 90    }
 91    @Override
 92    public String toString() {
 93       return String.format("%s\nBasic Salary: $%,.2f",
 94          super.toString(),getBasicSalary());
 95    }
 96 }
 97  
 98 package org.mano.example;
 99 public class HourlyEmployee extends Employee {
100    protected double wage;
101    protected double hours;
102    public HourlyEmployee(String name, String ssn,
103    double wage, double hours) {
104       super (name, ssn);
105       setWage(wage);
106       setHours(hours);
107    }
108    public double getWage() {
109       return wage;
110    }
111    public void setWage(double wage) {
112       if(wage >= 0.0)
113          this.wage = wage;
114       else
115          throw new IllegalArgumentException("wage " +
116             "must be > 0.0");
117    }
118    public double getHours() {
119       return hours;
120    }
121    public void setHours(double hours) {
122       if(hours >= 0.0)
123          this.hours = hours;
124       else
125          throw new IllegalArgumentException("hours "  +
126             "must be > 0.0");
127    }
128    @Override
129    public double salary() {
130       return getHours() * getWage();
131    }
132    @Override
133    public String toString() {
134       return String.format("%s\nWage: $%,
135          .2f\nHours worked: %,.2f",
136          super.toString(),getWage(),getHours());
137    }
138 }
139  
140 package org.mano.example;
141 public class CommissionEmployee extends Employee {
142    protected double sales;
143    protected double commission;
144    public CommissionEmployee(String name, String ssn,
145          double sales, double commission) {
146       super(name, ssn);
147       setSales(sales);
148       setCommission(commission);
149    }
150    public double getSales() {
151       return sales;
152    }
153    public void setSales(double sales) {
154       if(sales >=0.0)
155          this.sales = sales;
156       else
157          throw new IllegalArgumentException("Sales " +
158             "must be >= 0.0");
159    }
160    public double getCommission() {
161       return commission;
162    }
163    public void setCommission(double commission) {
164       if(commission > 0.0 && commission < 1.0)
165          this.commission = commission;
166       else
167          throw new IllegalArgumentException("Commission " +
168             "must be between 0.0 and 1.0");
169    }
170    @Override
171    public double salary() {
172       return getCommission() * getSales();
173    }
174    @Override
175    public String toString() {
176       return String.format("%s\nSales: %,
177          .2f\nCommission: %,.2f",
178          super.toString(),getSales(),getCommission());
179    }
180 }

接口多态

接口的多态性与前面的示例非常相似，不同之处在于，这里的多态性规则是根据Java接口指定的规范进行的。接口名称可以用作引用变量，就像我们对上面的类名称所做的那样。它引用实现该接口的任何类的任何对象。这是一个例子。

 1 package org.mano.example;
 2 public interface Player {
 3    public enum STATUS{PLAY,PAUSE,STOP};
 4    public void play();
 5    public void stop();
 6    public void pause();
 7 }
 8  
 9 package org.mano.example;
10 public class VideoPlayer implements Player {
11    private STATUS currentStatus = STATUS.STOP;
12    @Override
13    public void play() {
14       if(currentStatus == STATUS.STOP ||
15             currentStatus == STATUS.PAUSE) {
16          currentStatus = STATUS.PLAY;
17          System.out.println("Playing Video...");
18       }
19       else
20          System.out.println("I am ON playing man!");
21    }
22    @Override
23    public voidstop() {
24       if(currentStatus == STATUS.PLAY ||
25             currentStatus == STATUS.PAUSE) {
26          currentStatus = STATUS.STOP;
27          System.out.println("Video play stopped.");
28       }
29       else
30          System.out.println("Do you want me to go fishing?");
31    }
32    @Override
33    public void pause() {
34       if(currentStatus == STATUS.PLAY) {
35          currentStatus = STATUS.PAUSE;
36          System.out.println("Video play paused.");
37       }
38       else
39          System.out.println("I'm a statue. You froze me
40             already!");
41       }
42    }
43  
44 package org.mano.example;
45 public class AudioPlayer implements Player {
46    private STATUS currentStatus = STATUS.STOP;
47    @Override
48    public void play() {
49       if(currentStatus == STATUS.STOP ||
50             currentStatus == STATUS.PAUSE) {
51          currentStatus = STATUS.PLAY;
52          System.out.println("Playing Audio...");
53       }
54       else
55          System.out.println("I am ON playing man!");
56    }
57    @Override
58    public void stop() {
59       if(currentStatus == STATUS.PLAY ||
60             currentStatus == STATUS.PAUSE) {
61          currentStatus = STATUS.STOP;
62          System.out.println("Audio play stopped.");
63       }
64       else
65          System.out.println("Do you want me to go fishing?");
66    }
67    @Override
68    public void pause() {
69       if(currentStatus == STATUS.PLAY) {
70          currentStatus = STATUS.PAUSE;
71          System.out.println("Audio play paused.");
72       }
73       else
74          System.out.println("I'm a statue. You froze me
75             already!");
76       }
77    }
78  
79 package org.mano.example;
80 public class PlayerApp {
81    public static void main(String[] args) {
82       Player player= new VideoPlayer();
83       player.play();
84       player.pause();
85       player.stop();
86       player= new AudioPlayer();
87       player.play();
88       player.pause();
89       player.stop();
90    }
91 }