Jdk8新特性之4大函数式接口

@FunctionalInterface
public interface Supplier<T> {

    /**
     * Gets a result.
     *
     * @return a result
     */
    T get();
}

@FunctionalInterface
public interface Consumer<T> {

    /**
     * Performs this operation on the given argument.
     *
     * @param t the input argument
     */
    void accept(T t);

}

@FunctionalInterface
public interface Function<T, R> {

    /**
     * Applies this function to the given argument.
     *
     * @param t the function argument
     * @return the function result
     */
    R apply(T t);

}

@FunctionalInterface
public interface Predicate<T> {

    /**
     * Evaluates this predicate on the given argument.
     *
     * @param t the input argument
     * @return {@code true} if the input argument matches the predicate,
     * otherwise {@code false}
     */
    boolean test(T t);
}

/**
 * @author WGR
 * @create 2020/3/24 -- 21:46
 */
public class Demo02Supplier {
    // 使用Lambda表达式返回数组元素最大值
    public static void main(String[] args) {
        System.out.println("开始了");
        printMax(() -> {
            int[] arr = {11, 99, 88, 77, 22};
            Arrays.sort(arr); // 升序排序
            return arr[arr.length - 1];
        });
    }

    public static void printMax(Supplier<Integer> supplier) {
        System.out.println("aa");
        int max = supplier.get();
        System.out.println("max = " + max);
    }
}

public class Demo03Consumer {

    public static void main(String[] args) {
        printHello( str ->{
            //HELLO JDK8
            System.out.println(str.toUpperCase());
        });
    }

    public static void printHello(Consumer<String> consumer) {
        consumer.accept("hello jdk8");
    }
}

public class Demo04ConsumerAndThen {

    public static void main(String[] args) {
        printHello( str1 ->{
            System.out.println(str1.toUpperCase());
        },str2 ->{
            System.out.println(str2.toLowerCase());
        });
    }

    public static void printHello(Consumer<String> c1, Consumer<String> c2) {
        String str = "Hello Jdk8";
//        default Consumer<T> andThen(Consumer<? super T> after) {
//            Objects.requireNonNull(after);
//            return (T t) -> { accept(t); after.accept(t); };
//        }
        c2.andThen(c1).accept(str);
    }
}

public class Demo05Function {

    public static void main(String[] args) {
        getNumber( str ->{
            return Integer.parseInt(str);
        });
    }

    public static void getNumber(Function<String, Integer> function) {
        String num = "20";
        Integer apply = function.apply(num);
        System.out.println(apply);
    }
}

public class Demo06FunctionAndThen {

    public static void main(String[] args) {
        getNumber(str -> {
            return Integer.parseInt(str);
        }, num -> {
            return num * 5;
        });
    }

    public static void getNumber(Function<String, Integer> f1, Function<Integer, Integer> f2) {
        String num = "20";
        Integer integer = f1.andThen(f2).apply(num);
        System.out.println(integer);   //100
    }
}

public class Demo07Predicate {
    public static void main(String[] args) {
        isLongName( str -> {
            return str.length() > 3;
        });
    }

    public static void isLongName(Predicate<String> predicate) {
        boolean test = predicate.test("新年快乐");
        System.out.println(test);
    }
}

public class Demo08Predicate_And_Or_Negate {
    // 使用Lambda表达式判断一个字符串中即包含W,也包含H
    // 使用Lambda表达式判断一个字符串中包含W或者包含H
    // 使用Lambda表达式判断一个字符串中不包含W
    public static void main(String[] args) {
        test((String str) -> {
            // 判断是否包含W
            return str.contains("W");
        }, (String str) -> {
            // 判断是否包含H
            return str.contains("H");
        });
    }

    public static void test(Predicate<String> p1, Predicate<String> p2) {

        String str = "Hello World";
        boolean b = p1.and(p2).test(str);
        if (b) {
            System.out.println("即包含W,也包含H");
        }

        // 使用Lambda表达式判断一个字符串中包含W或者包含H
        boolean b1 = p1.or(p2).test(str);
        if (b1) {
            System.out.println("包含W或者包含H");
        }
        // 使用Lambda表达式判断一个字符串中不包含W
        boolean b2 = p1.negate().test("Hello W");
        // negate相当于取反 !boolean
        if (b2) {
            System.out.println("不包含W");
        }
    }
}