compareTo源码解读

/**
     * Compares two strings lexicographically.
     * The comparison is based on the Unicode value of each character in
     * the strings. The character sequence represented by this
     * <code>String</code> object is compared lexicographically to the
     * character sequence represented by the argument string. The result is
     * a negative integer if this <code>String</code> object
     * lexicographically precedes the argument string. The result is a
     * positive integer if this <code>String</code> object lexicographically
     * follows the argument string. The result is zero if the strings
     * are equal; <code>compareTo</code> returns <code>0</code> exactly when
     * the {@link #equals(Object)} method would return <code>true</code>.
     * <p>
     * This is the definition of lexicographic ordering. If two strings are
     * different, then either they have different characters at some index
     * that is a valid index for both strings, or their lengths are different,
     * or both. If they have different characters at one or more index
     * positions, let <i>k</i> be the smallest such index; then the string
     * whose character at position <i>k</i> has the smaller value, as
     * determined by using the &lt; operator, lexicographically precedes the
     * other string. In this case, <code>compareTo</code> returns the
     * difference of the two character values at position <code>k</code> in
     * the two string -- that is, the value:
     * <blockquote><pre>
     * this.charAt(k)-anotherString.charAt(k)
     * </pre></blockquote>
     * If there is no index position at which they differ, then the shorter
     * string lexicographically precedes the longer string. In this case,
     * <code>compareTo</code> returns the difference of the lengths of the
     * strings -- that is, the value:
     * <blockquote><pre>
     * this.length()-anotherString.length()
     * </pre></blockquote>
     *
     * @param   anotherString   the <code>String</code> to be compared.
     * @return  the value <code>0</code> if the argument string is equal to
     *          this string; a value less than <code>0</code> if this string
     *          is lexicographically less than the string argument; and a
     *          value greater than <code>0</code> if this string is
     *          lexicographically greater than the string argument.
     */
    public int compareTo(String anotherString) {
	int len1 = count;
	int len2 = anotherString.count;
	int n = Math.min(len1, len2);
	char v1[] = value;
	char v2[] = anotherString.value;
	int i = offset;
	int j = anotherString.offset;

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

compareTo比较的是两个字符串的字典顺序，如果两个字符串的字典顺序相等，则返回0.如果此字符串比传入的参数字符串的字段顺序小则返回一个小于0的数，如果大则返回一个大于0的数。