实现Comparable接口下的唯一方法comparaTo()就可以比较类的大小，这些类包括java内置的包装类（Integer类，Character类等）、日期类和自定义的类(当然得自己实现Comparable接口，重写comparaTo方法)。
public interface Comparable<T> {
/**
* @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.
*/
public int compareTo(T o);
}
Integer类的比较,根据基本数据类型比较。
public int compareTo(Integer anotherInteger) {
return compare(this.value, anotherInteger.value);
}
public static int compare(int x, int y) {
return (x < y) ? -1 : ((x == y) ? 0 : 1);
}
Character类的比较，根据Unicode编码顺序比较。Unicode表中，序号30-39是数字“0,1，2···9”，序号65-90是大写字母“A，B，C···Z”，序号97-122是小写字母“a，b，c···z”。
public int compareTo(Character anotherCharacter) {
return compare(this.value, anotherCharacter.value);
}
public static int compare(char x, char y) {
return x - y;
}
String类的比较。如果一个字符串是另一个起始开始的子串，返回两个字符串的长度差，否则逐个比较字符的Unicode码大小，返回不相等时unicode码之差。
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;
}
例如abc和aBc比较，返回b和B的Unicode码之差32（98-66）.
