排序集合中的对象

1.源码介绍

1.1 Stream sorted()

源码查看：

/**
 * Returns a stream consisting of the elements of this stream, sorted
 * according to natural order.  If the elements of this stream are not
 * {@code Comparable}, a {@code java.lang.ClassCastException} may be thrown
 * when the terminal operation is executed.
 *
 * 
For ordered streams, the sort is stable.  For unordered streams, no
 * stability guarantees are made.
 *
 * 
This is a stateful
 * intermediate operation.
 *
 * @return the new stream
 */
Stream sorted();

说明：T 必须是实现了 Comparable 接口的类，否则方法会抛出 ClassCastException 异常。

1.2. Stream sorted(Comparator<? super T> comparator)

源码查看：

/**
 * Returns a stream consisting of the elements of this stream, sorted
 * according to the provided {@code Comparator}.
 *
 * 
For ordered streams, the sort is stable.  For unordered streams, no
 * stability guarantees are made.
 *
 * 
This is a stateful
 * intermediate operation.
 *
 * @param comparator a non-interfering,
 *                   stateless
 *                   {@code Comparator} to be used to compare stream elements
 * @return the new stream
 */
Stream sorted(Comparator<? super T> comparator);

说明：根据给定的 比较器 进行排序。Comparator是一个函数式接口，其源码如下（仅展示关键部分）：

@FunctionalInterface
public interface Comparator {
    /**
     * Compares its two arguments for order.  Returns a negative integer,
     * zero, or a positive integer as the first argument is less than, equal
     * to, or greater than the second.

     * 
     * ......（此处略去部分注释）
     *
     * @param o1 the first object to be compared.
     * @param o2 the second object to be compared.
     * @return a negative integer, zero, or a positive integer as the
     *         first argument is less than, equal to, or greater than the
     *         second.
     * @throws NullPointerException if an argument is null and this
     *         comparator does not permit null arguments
     * @throws ClassCastException if the arguments' types prevent them from
     *         being compared by this comparator.
     */
    int compare(T o1, T o2);

说明：方法的返回值分类以及含义如下：

• 负数：o1 小于 o2
• 0：o1 等于 o2
• 正数：o1 大于 o2

3. 使用

3.1 Stream sorted()

3.2 Stream sorted(Comparator<? super T> comparator)