46.函数式接口

1.概述

 

 

@FunctionalInterface
public interface FunctionInterface {
    void show();
}

2.函数式接口作为方法参数

public class Demo {
    public static void main(String[] args) {
        startThread(new Runnable() {
            @Override
            public void run() {
                System.out.println(Thread.currentThread().getName() + "启动一个线程");
            }
        });
        startThread(() -> System.out.println(Thread.currentThread().getName() + "启动一个线程"));
    }

    public static void startThread(Runnable runnable) {
        Thread thread = new Thread(runnable);
        thread.start();
    }
}

3.函数式接口作为返回值

    public static Comparator<String> getComparator() {
//        return new Comparator<String>() {
//            @Override
//            public int compare(String s1, String s2) {
//                return s1.length()-s2.length();
//            }
//        };
        return (s1,s2)->s1.length()-s2.length();
    }
        //      将下面集合中的字符串按照长度排序
        ArrayList<String> list = new ArrayList<>();
        list.add("aaa");
        list.add("aaaaa");
        list.add("aaaaaa");
        list.add("aaaa");
        System.out.println("排序之前:"+list);//[aaa, aaaaa, aaaaaa, aaaa]
        Collections.sort(list,getComparator());
        System.out.println("排序之后:"+list);//[aaa, aaaa, aaaaa, aaaaaa]

4.常用函数式接口

Supplier接口

public class Demo2 {
    public static void main(String[] args) {
        String str = getStr(new Supplier<String>() {
            @Override
            public String get() {
                return "字符串";
            }
        });
        System.out.println(str);
        String str1 = getStr(() -> "字符串");
        System.out.println(str1);
    }

    public static String getStr(Supplier<String> supplier) {
        return supplier.get();
    }
}

    public static Integer getMax(Supplier<Integer> supplier) {
        return supplier.get();
    }
        int []num={15,55,88,33,66};
        Integer max = getMax(new Supplier<Integer>() {
            @Override
            public Integer get() {
                int max = num[0];
                for (int i = 0; i < num.length; i++) {
                    if (num[i] > max) {
                        max = num[i];
                    }
                }
                return max;
            }
        });
        Integer max1 = getMax(() -> {
            int maxValue = num[0];
            for (int i = 0; i < num.length; i++) {
                if (num[i] > maxValue) {
                    maxValue = num[i];
                }
            }
            return maxValue;
        });
        System.out.println(max);
        System.out.println(max1);

Consumer接口

public class ConsumerDemo {
    public static void main(String[] args) {
        opertorStr("林青霞", s -> System.out.println(s));//林青霞
        opertorStr2("周星驰", s -> System.out.println(s), s -> System.out.println(new StringBuilder(s).reverse().toString()));//周星驰驰星周
        String s[] = {"林青霞,18", "周星驰,58", "云舒,17"};
        opertorStrArr(s, str -> System.out.print("姓名:" + str.split(",")[0]),
                str -> System.out.println(",年龄:" + str.split(",")[1]));
    }

    //      1.定义一个方法消费一个字符串
    public static void opertorStr(String s, Consumer<String> consumer) {
        consumer.accept(s);
    }

    //    2.定义一个方法消费两次字符串
    public static void opertorStr2(String s, Consumer<String> consumer1, Consumer<String> consumer2) {
//    consumer1.accept(s);
//    consumer2.accept(s);
        consumer1.andThen(consumer2).accept(s);
    }

    //    3.消费一个字符串数组
    public static void opertorStrArr(String[] s, Consumer<String> consumer1, Consumer<String> consumer2) {
//    consumer1.accept(s);
//    consumer2.accept(s);
        for (String str : s) {
            consumer1.andThen(consumer2).accept(str);
        }

    }

Predicate接口

public class PredicateDemo {
    public static void main(String[] args) {
        boolean b1 = checkStr("hello", s -> s.length() > 8);
        System.out.println(b1);

        boolean b2 = checkStr2("helloWorld", s -> s.length() > 8, s -> s.length() < 15);
        System.out.println(b2);
    }

    public static boolean checkStr(String s, Predicate<String> predicate) {
        return predicate.test(s);
//        return predicate.negate().test(s);//对test结果取非操作
    }

    //    同一个字符串给出两个判断,两个判断结果进行逻辑运算之后返回
    public static boolean checkStr2(String s, Predicate<String> predicate1, Predicate<String> predicate2) {
//    boolean b1= predicate1.test(s);
//    boolean b2= predicate2.test(s);
//    return b1&&b2;
        return predicate1.and(predicate2).test(s);
    }
}

        String s[] = {"林青霞,25", "周星驰,55", "成龙,60", "胡歌,30"};
        ArrayList<String> strings = checkArr(s, s1 -> s1.split(",")[0].length() > 2, s1 -> Integer.parseInt(s1.split(",")[1]) < 26);
        for (String str : strings) {
            System.out.println(str);
        }
    public static ArrayList<String> checkArr(String s[], Predicate<String> predicate1, Predicate<String> predicate2) {
        ArrayList<String> strings = new ArrayList<>();
        for (String str : s) {
            if (predicate1.and(predicate2).test(str)) {
                strings.add(str);
            }
        }
        return strings;
    }

Funftion接口

public class FunftionDemo {
    public static void main(String[] args) {
        convert("100", s -> Integer.parseInt(s));
        convert("100", s -> Integer.parseInt(s) + 500, s -> String.valueOf(s));
    }

    public static void convert(String s, Function<String, Integer> function) {
        Integer apply = function.apply(s);
        System.out.println(apply);
    }
//Function<String,Integer>:String(泛型1)是apply()方法输入的参数类型,Integer(泛型2)是apply()方法输出的类型
    public static void convert(String s, Function<String, Integer> f1, Function<Integer, String> f2) {
//        Integer apply1 = f1.apply(s);
//        String apply2 = f2.apply(apply1);
//        System.out.println(apply2);
        String s1 = f1.andThen(f2).apply(s);//将f1的apply返回结果作为f2的apply()方法的参数
        System.out.println(s1);
    }
}

 

Function<String, Integer>