一、简要描述

• 使用Lambda的前提

        必须有一个函数式接口: 有且只有一个抽象方法的接口

        @FunctionnalInterface注解

• 常见的函数式接口
  • Runnable / Callable
  • Supplier / Consumer
  • Comparator
  • Predicate
  • Function

二、代码实现

1、Runnable - RunnableLambda测试类

package tech.flygo.lambda.demo3;

/**
 * @description: Runnable Lambda测试类
 * @author: flygo
 * @time: 2023/5/13 19:52
 */
public class RunnableLambda {

    public static void main(String[] args) {
        // 实现匿名内部类的方式，实现多线程
        new Thread(new Runnable() {
            @Override
            public void run() {
                String name = Thread.currentThread().getName();
                System.out.println(name + "线程已启动");
            }
        }).start();

        // 使用Lambda表达式，实现多线程
        new Thread(() -> {
            String name = Thread.currentThread().getName();
            System.out.println(name + "线程已启动");
        }).start();

        // 使用优化的Lambda实现多线程
        new Thread(() -> System.out.println(Thread.currentThread().getName())).start();
    }
}

2、Supplier - SupplierLambda 测试类

package tech.flygo.lambda.demo3;

import java.util.function.Supplier;

/**
 * @description: 提供者Lambda测试类
 * @author: flygo
 * @time: 2023/5/13 20:05
 */
public class SupplierLambda {

    public static void main(String[] args) {
        int[] array = {3, 4, 8, 99, 444};

        // 调用getMax方法，参数传递Lambda
        int maxNum = getMax(() -> {
            int temp = array[0];

            // 查找数组的最大值
            for (int i : array) {
                if (temp < i) {
                    temp = i;
                }
            }
            return temp;
        });
        
        System.out.println(maxNum);
    }

    // 定义一个方法的参数传递Supplier传递使用泛型Integer
    public static int getMax(Supplier<Integer> supplier) {
        return supplier.get();
    }
}

3、Consumer - ConsumerLambda 测试类

package tech.flygo.lambda.demo3;

import java.util.function.Consumer;

/**
 * @description: 消费者Lambda测试类
 * @author: flygo
 * @time: 2023/5/13 20:21
 */
public class ConsumerLambda {

    public static void main(String[] args) {
//        consumerString(s -> System.out.println(s));

        consumerString(
                s -> System.out.println(s.toUpperCase()),
                s -> System.out.println(s.toLowerCase())
        );
    }

    static void consumerString(Consumer<String> consumer) {
        consumer.accept("Hello");
    }

    static void consumerString(Consumer<String> one, Consumer<String> two) {
        one.andThen(two).accept("Hello");
    }

}

4、Comparator - ComparatorLambda测试类

package tech.flygo.lambda.demo3;

import java.util.Arrays;
import java.util.Comparator;

/**
 * @description: 比较器Lambda测试类
 * @author: flygo
 * @time: 2023/5/13 20:32
 */
public class ComparatorLambda {

    public static void main(String[] args) {
        String[] strs = {"adbc", "avc", "de", "dfafafdd"};

        // 使用匿名内部类的方式，实现比较器
        Comparator<String> comparator = new Comparator<String>() {
            @Override
            public int compare(String o1, String o2) {
                return o1.length() - o2.length();
            }
        };
        Arrays.sort(strs, comparator);
        System.out.println(Arrays.toString(strs));

        // 使用Lambda表达式实现
        Arrays.sort(strs, (o1, o2) -> o1.length() - o2.length());
        System.out.println(Arrays.toString(strs));

        Arrays.sort(strs, Comparator.comparingInt(String::length));
        System.out.println(Arrays.toString(strs));
    }
}

5、Predicate - PredicateLambda测试类

package tech.flygo.lambda.demo3;

import java.util.function.Predicate;

/**
 * @description: 断言Lambda测试类
 * @author: flygo
 * @time: 2023/5/13 22:10
 */
public class PredicateLambda {

    public static void main(String[] args) {
        // 与运算
        andMethod(s -> s.contains("H"), s -> s.contains("W"));
        // 或运算
        orMethod(s -> s.contains("H"), s -> s.contains("W"));
        // 非运算
        negateMethod(s -> s.length() < 5);
    }

    static void andMethod(Predicate<String> one, Predicate<String> two) {
        boolean isValid = one.and(two).test("Helloworld");
        System.out.println("字符串符合要求吗：" + isValid);
    }

    static void orMethod(Predicate<String> one, Predicate<String> two) {
        boolean isValid = one.or(two).test("HelloWorld");
        System.out.println("字符串符合要求吗：" + isValid);
    }

    static void negateMethod(Predicate<String> predicate) {
        boolean validLength = predicate.negate().test("HelloWorld");
        System.out.println("字符串很长吗？" + validLength);
    }
}

6、Function - FunctionLambda测试类

package tech.flygo.lambda.demo3;

import java.util.function.Function;

/**
 * @description: 函数Lambda测试类
 * @author: flygo
 * @time: 2023/5/13 22:21
 */
public class FunctionLambda {

    public static void main(String[] args) {

        // 传入的值为10，one Function 第一个 10 + 10 = 20，返回值20作为two函数的值进行处理 20 * 10 = 200
        method(s -> Integer.parseInt(s) + 10, i -> i * 10);
        
        String str = "张三,18";
        int age = getAgeNum(str, s -> s.split(",")[1],
                s -> Integer.parseInt(s),
                n -> n += 100);
        System.out.println(age);

    }

    static void method(Function<String, Integer> one, Function<Integer, Integer> two) {
        int num = one.andThen(two).apply("10");
        System.out.println(num + 20);
    }

    static int getAgeNum(String str, Function<String, String> one,
                         Function<String, Integer> two,
                         Function<Integer, Integer> three) {
        return one.andThen(two).andThen(three).apply(str);
    }
}