1.字符串String是怎么排序的絮宁?
下面的代碼媳拴,userName是String型的
userList.stream().sorted(Comparator.comparing(User::getUsername).reversed()).collect(Collectors.toList());
Comparator 類中的comparing方法治力,入?yún)魅隖unction碱鳞,用限界表達(dá)式限定傳入的類型侵佃,通過Function的apply方法獲取值麻昼。
public static <T, U extends Comparable<? super U>> Comparator<T> comparing(
Function<? super T, ? extends U> keyExtractor)
{
Objects.requireNonNull(keyExtractor);
return (Comparator<T> & Serializable)
(c1, c2) -> keyExtractor.apply(c1).compareTo(keyExtractor.apply(c2));
}
這是String的比較方法,仔細(xì)分析馋辈,他是將兩個字符串先轉(zhuǎn)成char型抚芦,再逐一對比char,做減法迈螟,利用char型在java中是UTF-8編碼燕垃,而UTF-8編碼在0~128是和ASCII編碼是一致的,A-Z 65-90 a-z 96-122 所以大寫字母是在小寫字母之前的
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;
}