通过行为参数传递代码

Posted 2023-01-03

一、概述

1.1、行为参数化的含义：让方法接受多种行为作为参数，并在内部使用，来完成不同行为。

1.2、案例：我们要得到重量大于150克的苹果和所有的绿苹果。

二、代码实现

2.1 行为参数化

package com.jdk.test;

public class Apple 
private String color;
private int weight;
public String getColor() 
  return color;

public void setColor(String color) 
  this.color = color;

public int getWeight() 
  return weight;

public void setWeight(int weight) 
  this.weight = weight;

public Apple(String color, int weight) 
  super();
  this.color = color;
  this.weight = weight;

@Override
public String toString() 
  return "Apple [color=" + color + ", weight=" + weight + "]";

package com.jdk.test;
/**
 * 
 * @author Administrator
 *策略模式的应用
 *行为参数化：让方法接受多种行为作为参数,并在内部使用,来完成不同的行为。
 */
public interface ApplePredicate 
  
  boolean  test(Apple apple);

package com.jdk.test;

public class AppleGreenColorPredicate implements ApplePredicate 

  @Override
  public boolean test(Apple apple) 
    //选出绿色的苹果
    return "green".equals(apple.getColor());
  

package com.jdk.test;

public class AppleHeavyWeightPredicate implements ApplePredicate 

  @Override
  public boolean test(Apple apple) 
    //选出大于150克的苹果
    return apple.getWeight() > 150;
  

package com.jdk.test;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class FilteringApples 
  
public static void main(String[] args) 
  List<Apple> inventory = Arrays.asList(new Apple("green",80),
      new Apple("red",190),
      new Apple("green",100));
  
  List<Apple> heavryApples = filterApples(inventory,new AppleHeavyWeightPredicate());
  heavryApples.forEach(Apple -> System.out.println("输出重量大于150克"+Apple.toString()));
  List<Apple> greenApples = filterApples(inventory,new AppleGreenColorPredicate()); 
  greenApples.forEach(Apple -> System.out.println("输出绿色的Apple"+Apple.toString()));


public static List<Apple> filterApples(List<Apple> inventory,ApplePredicate p) 
  List<Apple>  result=new ArrayList<>();
  for (Apple apple : inventory) 
    if(p.test(apple)) 
      result.add(apple);
    
  
  return result;

 

以上是我们使用行为参数化来实现的需求，下面我们来看下使用匿名内部类的实现方式：

List<Apple> redApples = filterApples(inventory,new ApplePredicate() 
    @Override
    public boolean test(Apple apple) 
      return "red".equals(apple.getColor());
    
  );
redApples.forEach(Apple ->System.out.println("输出红色Apple"+Apple.toString()));

使用了匿名内部类并没有让我们感到代码的简洁和易读，我们再对上面的代码进行改造。

2.2使用Lambda表达式

List<Apple> greenApples = filterApples(inventory, (Apple apple) -> "green".equals(apple.getColor()));
greenApples.forEach(Apple -> System.out.println("使用Lambda表达式"+Apple.toString()));

//按照大小升序排序

greenApples.sort((Apple a1,Apple a2) -> a1.getMax().compareTo(a2.getMax()));

这段代码看起来是不是清晰多了，这就是JDK8中的

Lambda表达式的写法。

三、总结

通过上面的案例我们已经熟悉了JDK8中的Lambda表达式的写法，我们可以将filter方法进行提取让它变成一个公共

的代码块，而不仅仅是过滤Apple了。

public interface Predicate<T> 
boolean test(T t);
public static <T> List<T> filter(List<T> inventory,Predicate<T> p) 
  List<T>  result=new ArrayList<>();
  for (T t : inventory) 
    if(p.test(t)) 
      result.add(t);
    
  
  return result;