Comparator 和 Comparable 比较

Comparator 是一个比较器，而Comparable是支持排序的一个标识，如果某一个类实现了Comparable则表示类支持排序，且排序方式为‘接口提供’。
Comparator是一个比较器， 相当与一个自定义的比较方式,所以不能运用在通用工具中，一般地， 我们使用比较器来比较两个对象的时候，需要借用外部力量，比如内部类实现Comparator，提供compare方法实现。

当我们在后期才会考虑到该类对象需要排序的时候，那么我们可以考虑使用Comparator 自定义个比较器，然后达到排序的目的， 比如String 的忽略大小写比较字符串.

/**
     * A Comparator that orders String objects as by
     * compareToIgnoreCase. This comparator is serializable.
     * 

     * Note that this Comparator does not take locale into account,
     * and will result in an unsatisfactory ordering for certain locales.
     * The java.text package provides Collators to allow
     * locale-sensitive ordering.
     *
     * @see     java.text.Collator#compare(String, String)
     * @since   1.2
     */
    public static final Comparator CASE_INSENSITIVE_ORDER
                                         = new CaseInsensitiveComparator();
    private static class CaseInsensitiveComparator
                         implements Comparator, java.io.Serializable {
    // use serialVersionUID from JDK 1.2.2 for interoperability
    private static final long serialVersionUID = 8575799808933029326L;

        public int compare(String s1, String s2) {
            int n1=s1.length(), n2=s2.length();
            for (int i1=0, i2=0; i1compareTo with normalized versions of the strings
     * where case differences have been eliminated by calling
     * Character.toLowerCase(Character.toUpperCase(character)) on
     * each character.
     * 

     * Note that this method does not take locale into account,
     * and will result in an unsatisfactory ordering for certain locales.
     * The java.text package provides collators to allow
     * locale-sensitive ordering.
     *
     * @param   str   the String to be compared.
     * @return  a negative integer, zero, or a positive integer as the
     *      specified String is greater than, equal to, or less
     *      than this String, ignoring case considerations.
     * @see     java.text.Collator#compare(String, String)
     * @since   1.2
     */
    public int compareToIgnoreCase(String str) {
        return CASE_INSENSITIVE_ORDER.compare(this, str);
    }