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java sort default order

· 2 min read

背景​

java 的Array.sort()或者.stream.sorted() 都会使用Comparable<T> 作为参数
目前需要了解这些排序函数究竟是升序还是降序的

一句话答案​

所有的排序都是升序的ascending

原因​

Array.sort() , .stream.sorted() 都使用Comparable<T>这个类,都需要实现接口int compare(T o1, T o2);

我们看看接口compare的注释:

Params:
o1 – the first object to be compared. o2 – the second object to be compared.
Returns:
a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second.
int compare(T o1, T o2);

入参有两个:第一个参数o1,第二个是o2 返回值:

  • 如果o1 < o2 返回 负数
  • 如果o1 > o2 返回正数
  • 如果o1 = o2,返回0

再看看注释java.util.Comparator<T> , 默认都是natural ordering

    /**
     * Returns a comparator that imposes the reverse of the <em>natural
     * ordering</em>.
     *
     * <p>The returned comparator is serializable and throws {@link
     * NullPointerException} when comparing {@code null}.
     *
     * @param  <T> the {@link Comparable} type of element to be compared
     * @return a comparator that imposes the reverse of the <i>natural
     *         ordering</i> on {@code Comparable} objects.
     * @see Comparable
     * @since 1.8
     */
    public static <T extends Comparable<? super T>> Comparator<T> reverseOrder() {
        return Collections.reverseOrder();
    }


相关阅读​

自然排序说明 stackoverflow