函数式接口

参考：https://juejin.im/post/5a69373ef265da3e5661b62b#heading-2

@Data
public class Book {

    String author;

    Double money;

    public Book(String author, double money) {
        this.author = author;
        this.money = money;

    }
}

    public static <T, R> List<R>  map(List<T> list, Function<T, R> f) {
        List<R> result = new ArrayList<>();
        for(T s: list){
            result.add(f.apply(s));
        }
        return result;
    }


    public static void main(String[] args) {

        List<Book> books = Arrays.asList(
                new Book("张三", 99.00D),
                new Book("李老四", 59.00D),
                new Book("王二麻子", 59.00D)
        );
        List<Integer> results = map(books, book -> book.getAuthor().length());
        System.out.println(results.toString());

    }

    static void modifyTheValue(int valueToBeOperated, Function<Integer, Integer> function){

        int newValue = function.apply(valueToBeOperated);

        System.out.println(newValue);

    }

    public static void main(String[] args) {

        int incr = 20;  int myNumber = 10;

        modifyTheValue(myNumber, val-> val + incr);

        myNumber = 15;  modifyTheValue(myNumber, val-> val * 10);

        modifyTheValue(myNumber, val-> val - 100);

        modifyTheValue(myNumber, val-> "somestring".length() + val - 100);

    }

f.apply(s)，s是参数，对参数执行f操作，返回操作后的结果。