函数式接口

Function函数式接口

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Function function = new Function<String, String>() {

    @Override
    public String apply(String str) {
        return str;
    }
};

// 使用lamba简化
function = (str)->{
    return str;
};
System.out.println(function.apply("123"));

Predicate断定型接口

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Predicate<String> predicate = new Predicate<String>() {

    @Override
    public boolean test(String str) {
        return str.isEmpty();
    }
};

predicate = (str)->{
    return str.isEmpty();
};
System.out.println(predicate.test("33")); // false
System.out.println(predicate.test("")); // true

Consumer消费型接口

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Consumer<String>consumer = new Consumer<String>() {

    @Override
    public void accept(String str) {
        System.out.println(str);
    }
};

consumer = (str)->{System.out.println(str);};
consumer.accept("hello world..");

供给型接口

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Supplier<String> supplier = new Supplier<String>() {

    @Override
    public String get() {
        return "supper a str";
    }
};

supplier = ()->{return "supper a str by lambda";};
System.out.println(supplier.get());

stream流式计算

package com.test.fun;

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

public class Fun4 {

    public static void main(String[] args) {
        User u1 = new User(1, "aa", 21);
        User u2 = new User(2, "bb", 22);
        User u3 = new User(3, "cc", 23);
        User u4 = new User(4, "dd", 24);
        User u5 = new User(5, "ee", 25);
        User u6 = new User(6, "ee", 26);
        /**
         * 筛选：
         * 1. id必须是偶数
         * 2. 年龄必须大于23岁
         * 3. 用户名转为大写字母
         * 4. 用户名字母倒着排序
         * 5. 只输出一个用户
         */
        List<User> list = Arrays.asList(u1, u2, u3, u4, u5, u6);
        list.stream().filter((u)->{return u.getId()% 2==0;})
                     .filter((u)->{return u.getAge() > 23;})
                     .map(u->{return u.getName().toUpperCase();})
                     .sorted((uu1, uu2)->{return uu2.compareTo(uu1);})
                     .limit(1)
                     .forEach(System.out::println);
    }

}

class User {
    private int id;
    private String name;
    private int age;
    public User(int id, String name, int age) {
        this.id = id;
        this.name = name;
        this.age = age;
    }
    public int getId() {
        return id;
    }
    public String getName() {
        return name;
    }
    public int getAge() {
        return age;
    }
    @Override
    public String toString() {
        return "User [id=" + id + ", name=" + name + ", age=" + age + "]";
    }
}