java8之行为参数化

今天看到一块switch代码，觉得又臭又长，可以优化一下，只需要将函数名作为入参进行改造，有点类似于策略模式。

以下是使用Java8进行行为参数化的简单案例：

User.java

import lombok.Data;
import lombok.ToString;

@Data
@ToString
public class User {

    public User(Integer age) {
        this.age = age;
    }

    private Integer age;
}

UserPredicate.java

public interface CommonPredicate<T> {
    boolean test(T t);
}

Filter.java

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

public class Filter {

    /**
     * list 类型抽象化
     *
     * @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 t : list) {
            if (p.test(t)) {
                result.add(t);
            }
        }
        return result;
    }

    public List<User> oldUser(List<User> inventory) {
        return filter(inventory, (User user) -> user.getAge() > 50);
    }

    public List<User> youngUser(List<User> inventory) {
        return filter(inventory, (User user) -> user.getAge() < 20);
    }

    public static void main(String[] args) {
        List<User> userList = new ArrayList<>();
        userList.add(new User(11));
        userList.add(new User(21));
        userList.add(new User(31));
        userList.add(new User(41));
        userList.add(new User(51));
        userList.add(new User(61));

        Filter filter = new Filter();
        List<User> oldList = filter.oldUser(userList);
        oldList.forEach(r -> System.out.println(r.toString()));

        System.out.println("=======");
        List<User> youngerList = filter.youngUser(userList);
        youngerList.forEach(y -> System.out.println(y.toString()));
    }
}

Filter.java里面的main方法的输出结果如下：

User(age=51)
User(age=61)
=======
User(age=11)