20220406Java

记个笔记

字符串操作类中s1.compareTo(s)规则：

Compares two strings lexicographically. The comparison is based on the Unicode value of each character in the strings. The character sequence represented by this String object is compared lexicographically to the character sequence represented by the argument string. The result is a negative integer if this String object lexicographically precedes the argument string. The result is a positive integer if this String object lexicographically follows the argument string. The result is zero if the strings are equal; compareTo returns 0 exactly when the equals(Object) method would return true.

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 k be the smallest such index; then the string whose character at position k has the smaller value, as determined by using the < operator, lexicographically precedes the other string. In this case, compareTo returns the difference of the two character values at position k in the two string -- that is, the value:

 this.charAt(k)-anotherString.charAt(k)
 

If there is no index position at which they differ, then the shorter string lexicographically precedes the longer string. In this case, compareTo returns the difference of the lengths of the strings -- that is, the value:

 this.length()-anotherString.length()
 

1.当字符串s1和s都表示数字时，有三种结果-1（代表s1<s） ，  0（代表s与s1相等）  ，1（代表s1>s）。

2.当字符串s1和s不表示数字时，有三种结果负整数 （代表s1和s中的第一个不相同的字符的Unicode值相减为负数），0（代表s与s1相等） ，

正整数（代表s1和s中的第一个不相同的字符的Unicode值相减为正数）；若s1包含s（即s中的字符，s1都有），也有上述三种结果

但意义不同（除0表示相等）其中正整数表示s1包含s且长度大于s；反之为负整数。

3.Unicode中 a表示61   A表示41其它字母类推。

最后总结英语是有必要学的！