java 通过行为参数化传递代码，来解决不断增长的需求 ...

1， 通过定义不同的谓词接口来区分不同的苹果的重量，如果后续有更多的需求，只需要添加更多的谓词即可

1. package org.example;
4. import java.util.ArrayList;
5. import java.util.List;
7. enum Color {
8.     RED, GREEN, YELLOW
9. }
11. class Apple {
12.     private Integer weight;
13.     private Color color;
15.     public Apple(Integer weight, Color color) {
16.         this.weight = weight;
17.         this.color = color;
18.     }
20.     public Integer getWeight() {
21.         return weight;
22.     }
24.     public void setWeight(Integer weight) {
25.         this.weight = weight;
26.     }
28.     public Color getColor() {
29.         return color;
30.     }
32.     public void setColor(Color color) {
33.         this.color = color;
34.     }
35. }
37. interface ApplePredicate {
38.     boolean test(Apple apple);
39. }
41. class AppleGreenColorPredicate implements ApplePredicate {
42.     // 选择绿色苹果的谓词
43.     @Override
44.     public boolean test(Apple apple) {
45.         return Color.GREEN.equals(apple.getColor());
46.     }
47. }
49. class AppleHeavyWeightPredicate implements ApplePredicate {
50.     // 选择重量大于150克的谓词
51.     @Override
52.     public boolean test(Apple apple) {
53.         return apple.getWeight() > 150;
54.     }
55. }
58. public class Main {
60.     public static List<Apple> filterApples(List<Apple> inventory, ApplePredicate p) {
61.         // 通过谓词筛选苹果
62.         List<Apple> result = new ArrayList<>();
63.         for (Apple apple :
64.                 inventory) {
65.             if (p.test(apple)) {
66.                 result.add(apple);
67.             }
68.         }
69.         return result;
70.     }
73.     public static void main(String[] args) {
74.         List<Apple> inventory = new ArrayList<>();
75.         inventory.add(new Apple(300,Color.RED));
76.         inventory.add(new Apple(12,Color.RED));
77.         inventory.add(new Apple(350,Color.GREEN));
78.         inventory.add(new Apple(200,Color.YELLOW));
80.         // 方便的筛选绿色苹果和重苹果
81.         List<Apple> result = filterApples(inventory, new AppleGreenColorPredicate());
82.         result = filterApples(result, new AppleHeavyWeightPredicate());
83.         for (var apple :
84.                 result) {
85.             System.out.println(apple.getColor() + ":" + apple.getWeight());
86.         }
88.     }
89. }

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2，上述定义接口实现的方式过于啰嗦和繁杂可以使用匿名类和lamble表达式进行简化

2.1， 匿名内部类

1. List<Apple> result = filterApples(inventory, new ApplePredicate() {
2.     @Override
3.     public boolean test(Apple apple) {
4.         return Color.GREEN.equals(apple.getColor());
5.     }
6. });
7. result = filterApples(inventory, new ApplePredicate() {
8.     @Override
9.     public boolean test(Apple apple) {
10.         return apple.getWeight() > 150;
11.     }
12. });

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2.2 lamble表达式

1. List<Apple> result = filterApples(inventory, (Apple apple)->apple.getColor().equals(Color.GREEN));
2. result = filterApples(result, (Apple apple)->apple.getWeight()>150);

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3,更进一步的可以将针对苹果的list类型进行抽象化，用于其他的水果

1. interface Predicate <T>{
2.     boolean test(T t);
3. }
5. public static <T> List<T> filter(List<T> inventory, Predicate<T> p) {
6.     // 通过谓词筛选T
7.     List<T> result = new ArrayList<>();
8.     for (T e :
9.             inventory) {
10.         if (p.test(e)) {
11.             result.add(e);
12.         }
13.     }
14.     return result;
15. }

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