java:带有lambda表达式的Arrays.sort()

Question

我想months使用Arrays.sort方法按长度对数组中的String元素进行排序.我在这里被告知,可以使用lambda表达式而不是创建实现Comparator的新类.是否完全相同,但它不起作用.

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

public class MainClass {
public static void main(String[] args)
{

    String[] months = {"January","February","March","April","May","June","July","August","September","October","December"};

    System.out.println(Arrays.toString(months)); //printing before


    //neither this works:
    Arrays.sort(months, 
            (a, b) -> Integer.signum(a.length() - b.length())   
    );

    //nor this:
    Arrays.sort(months, 
            (String a, String b) -> { return Integer.signum(a.length() - b.length()) }; 
    );


    System.out.println(Arrays.toString(months)); //printing after
}
}

Answer 1

最干净的方式是:

Arrays.sort(months, Comparator.comparingInt(String::length));

或者,使用静态导入:

Arrays.sort(months, comparingInt(String::length));

但是,这也可以,但更详细:

Arrays.sort(months,
            (String a, String b) -> a.length() - b.length());

或更短:

Arrays.sort(months, (a, b) -> a.length() - b.length());

最后你的最后一个:

Arrays.sort(months, 
    (String a, String b) -> { return Integer.signum(a.length() - b.length()) }; 
);

有;错位的-它应该是:

Arrays.sort(months, 
    (String a, String b) -> { return Integer.signum(a.length() - b.length()); }
);