隊(duì)列排序常見(jiàn)的問(wèn)題總結(jié)

• Long類(lèi)型強(qiáng)制轉(zhuǎn)換問(wèn)題

   var addToQueueTime: Long

   fun compareTo(entity2: IBroadCastEntity): Int {
       return (entity2.addToQueueTime - addToQueueTime).toInt()
   }

該情況下long類(lèi)型強(qiáng)制轉(zhuǎn)換為int類(lèi)型，存在數(shù)據(jù)溢出隱患，本來(lái) entity2.addToQueueTime - addToQueueTime > 0的，結(jié)果數(shù)據(jù) 溢出后可能為 負(fù)值，從而產(chǎn)生相反的排序結(jié)果

• 漏掉==的情況

data class ImChatMsgItem(
    var userId: Long = 0,
    var avatar: String = "",
    var name: String = "",
    var lastMsg: String = "",
    var lastMsgTime: Long = 0,
) : Comparable<ImChatMsgItem> {
    override fun compareTo(other: MsgItem): Int {
        return if (other.lastMsgTime - lastMsgTime > 0) {
            1
        } else {
            -1
        }
    }
}

該情況下，漏掉了相等的情況，會(huì)引發(fā)相應(yīng)的報(bào)錯(cuò)

java.lang.IllegalArgumentException: Comparison method violates its general contract!
    at java.util.ComparableTimSort.mergeHi(ComparableTimSort.java:866)
    at java.util.ComparableTimSort.mergeAt(ComparableTimSort.java:483)
    at java.util.ComparableTimSort.mergeForceCollapse(ComparableTimSort.java:422)
    at java.util.ComparableTimSort.sort(ComparableTimSort.java:222)
    at java.util.Arrays.sort(Arrays.java:1302)
    at java.util.Arrays.sort(Arrays.java:1485)
    at java.util.ArrayList.sort(ArrayList.java:1470)
    at java.util.Collections.sort(Collections.java:206)
    at java.util.Collections.sort(Collections.java:159)
    at kotlin.collections.CollectionsKt__MutableCollectionsJVMKt.sort((MutableCollectionsJVM.kt:31) (#pluginId:host#)

到這里不得提下，java中對(duì)比的3原則

自反性：當(dāng) 兩個(gè)相同的元素相比時(shí)，compare必須返回0，也就是compare(o1, o1) = 0;

反對(duì)稱(chēng)性：如果compare(o1,o2) = 1，則compare(o2, o1)必須返回符號(hào)相反的值也就是 -1；

傳遞性：如果 a>b, b>c, 則 a必然大于c。也就是compare(a,b)>0, compare(b,c)>0, 則compare(a,c)>0

上面這個(gè)用列就是違反自反性原則，導(dǎo)致的報(bào)錯(cuò)

總結(jié)下升序和降序的總結(jié)

class MyComparator implements Comparator<A> {

    @Override
    public int compare(A o1, A o2) {
        //升序
        //return o1.a - o2.a;
        //降序：后面會(huì)具體分析為什么降序
        return o2.a - o1.a;
    }
}