Comparable接口和Coma

Comparable接口中只申明了一个方法public int compareTo(Object o)

* @param   o the object to be compared.
* @return  a negative integer, zero, or a positive integer as this object
*          is less than, equal to, or greater than the specified object.
*
* @throws NullPointerException if the specified object is null
* @throws ClassCastException if the specified object's type prevents it
*         from being compared to this object.
类实现了Comparable接口说明这个类的对象是能够进行比较的。

“实现Comparable接口的类的对象的List列表(或数组)”，则该List列表(或数组)可以通过 Collections.sort（或 Arrays.sort）进行排序。

此外，“实现Comparable接口的类的对象”可以用作“有序映射(如TreeMap)”中的键或“有序集合(TreeSet)”中的元素，而不需要指定比较器。

如String类就实现了comarable接口

public int compareTo(String anotherString) {
    int len1 = value.length;
    int len2 = anotherString.value.length;
    int lim = Math.min(len1, len2);
    char v1[] = value;
    char v2[] = anotherString.value;

    int k = 0;
    while (k < lim) {
        char c1 = v1[k];
        char c2 = v2[k];
        if (c1 != c2) {
            return c1 - c2;
        }
        k++;
    }
    return len1 - len2;
}