public interface ApplePredicate {
    /**
    * 謂詞（選擇標準）
    * @param apple
    * @return
    */
    boolean test(Apple apple);
}

public class AppleWeightPredicate implements ApplePredicate{
    @Override
    public boolean test(Apple apple) {
        return apple.getWeight() > 150;
    }
}

public class AppleGreenColorPredicate implements ApplePredicate{
    @Override
    public boolean test(Apple apple) {
        return "green".equals(apple.getColor());
    }
}

public class FilterApples {
    /**
    * ApplePredicate參數實現了行為參數化
    * @param inventory
    * @param p
    * @return
    */
    public static List<Apple> filterApples(List<Apple> inventory, ApplePredicate p) {
        List<Apple> result = new ArrayList<Apple>();
        for (Apple apple : inventory) {
            if (p.test(apple)) {
                result.add(apple);
            }
        }
        return result;
    }
    
    /**
    * 匿名類實現
    * @param inventory
    * @return
    */
    public List<Apple> redApples(List<Apple> inventory) {
        return filterApples(inventory, new ApplePredicate() {
            @Override
            public boolean test(Apple apple) {
                return "red".equals(apple.getColor());
            }
        });
    }
    /**
    * 使用Lambda表達式
    * @param inventory
    * @return
    */
    public List<Apple> yellowApples(List<Apple> inventory) {
        return filterApples(inventory, (Apple apple) -> "yellow".equals(apple.getColor()));
    }
}

List類型抽象化：

public interface CommonPredicate<T> {
    /**
    * 類型抽象化
    * @param t
    * @return
    */
    boolean test(T t);
}

public class filter {
  /**
  * list類型抽象化
  * @param list
  * @param p
  * @param <T>
  * @return
  */
  public static <T> List<T> filter(List<T> list, CommonPredicate<T> p) {
        List<T> result = new ArrayList<T>();
    for (T e : list) {
      if (p.test(e)) {
        result.add(e);
      }
    }
    return result;
  }
    
  public List<Apple> redApples(List<Apple> inventory) {
    return filter(inventory, (Apple apple) -> "red".equals(apple.getColor()));
  }
    
  public List<Integer> main(List<Integer> inventory) {
      return filter(inventory, (Integer i) -> i % 2 == 0);
    }
}

行為參數化類似於策略設計模式。

Java8新特性之：行為參數化傳遞代碼