• 向上转型。去if、else，面向业务内容，优雅的将平面逻辑立体化。



1 package upperConvert;
 2 
 3 public class UpperConvert {
 4 
 5     /**
 6      * 向上转型
 7      */
 8     public static void main(String[] args) {
 9         UpperConvert.run(new LCDMonitor());
10         UpperConvert.run(new CRTMonitor());
11         UpperConvert.run(new PlasmaMonitor());
12     }
13 
14     public static void run(Monitor monitor) {
15         monitor.displayText();
16         monitor.displayGraphics();
17     }
18 
19 }
20 
21 class Monitor {
22     public void displayText() {
23     }
24 
25     public void displayGraphics() {
26     }
27 }
28 
29 class LCDMonitor extends Monitor {
30     public void displayText() {
31         System.out.println("LCD display text");
32     }
33 
34     public void displayGraphics() {
35         System.out.println("LCD display graphics");
36     }
37 }
38 
39 class CRTMonitor extends Monitor {
40     public void displayText() {
41         System.out.println("CRT display text");
42     }
43 
44     public void displayGraphics() {
45         System.out.println("CRT display graphics");
46     }
47 }
48 
49 class PlasmaMonitor extends Monitor {
50     public void displayText() {
51         System.out.println("Plasma display text");
52     }
53 
54     public void displayGraphics() {
55         System.out.println("Plasma display graphics");
56     }
57 }