Java 8 中 Function 接口使用方法介绍

// Java Function 接口的定义
@FunctionalInterface
public interface Function<T, R> {
R apply(T t);

default <V> Function<V, R> compose(Function<? super V, ? extends T> before) {
    Objects.requireNonNull(before);
    return (V v) -> apply(before.apply(v));
}

default <V> Function<T, V> andThen(Function<? super R, ? extends V> after) {
    Objects.requireNonNull(after);
    return (T t) -> after.apply(apply(t));
}

static <T> Function<T, T> identity() {
    return t -> t;
}

Function<Integer, Integer> add = p -> p + 10;
Integer result = add.apply(10);
// 这里会输出 20，因为这个函数定义的操作时把参数加上 10 后返回
System.out.println(result);

Function<Integer, Integer> multiplyTen = a -> a * 10;
Function<Integer, Integer> addTen = a -> a + 10;
// 先增加 10，然后再乘 10，输出结果 110
Function<Integer, Integer> addTenThenMultiplyTen = multiplyTen.compose(addTen);
System.out.println(addTenThenMultiplyTen.apply(1));

// 先乘 10，然后再加 10，输出结果 20
Function<Integer, Integer> multiplyTenAddTenThen = multiplyTen.andThen(addTen);
System.out.println(multiplyTenAddTenThen.apply(1));

public class CheckUtils {
    private static final Function<String, String> lengthCheck = params -> {
        if (params.length() > 100) {
            throw new RuntimeException("Length exceed max limit.");
        }
        return params;
    };

    private static final Function<String, String> invalidCharacterCheck = str -> {
        if (!str.matches("^[a-f,A-F]$")) {
            throw new RuntimeException("Contains invalid character.");
        }
        return str;
    };
    
    public static void checkStringLengthAndPhoneNumber(String string) {
        invalidCharacterCheck.compose(lengthCheck).apply(string);
    }
}