問題描述

我一直在這里和谷歌上發現從 long 到 int 而不是相反的問題.但我確信在從 int 到 Long 之前遇到這種情況的人不止我一個.

I keep finding both on here and Google people having troubles going from long to int and not the other way around. Yet I'm sure I'm not the only one that has run into this scenario before going from int to Long.

我發現的唯一其他答案是首先將其設置為 Long"，這確實沒有解決問題.

The only other answers I've found were "Just set it as Long in the first place" which really doesn't address the question.

我最初嘗試強制轉換，但得到Cannot cast from int to Long"

I initially tried casting but I get a "Cannot cast from int to Long"

for (int i = 0; i < myArrayList.size(); ++i ) {
    content = new Content();
    content.setDescription(myArrayList.get(i));
    content.setSequence((Long) i);
    session.save(content);
}

你可以想象我有點困惑，我被困在使用 int 因為一些內容是作為一個 ArrayList 和我的實體進入的m 存儲此信息需要序列號為 Long.

As you can imagine I'm a little perplexed, I'm stuck using int since some content is coming in as an ArrayList and the entity for which I'm storing this info requires the sequence number as a Long.

推薦答案

請注意，轉換為 long 和轉換為 Long 之間存在差異.如果你轉換成 long (一個原始值)，那么它應該被自動裝箱成一個 Long (包裝它的引用類型).

Note that there is a difference between a cast to long and a cast to Long. If you cast to long (a primitive value) then it should be automatically boxed to a Long (the reference type that wraps it).

您也可以使用 new 創建 Long 的實例，并使用 int 值對其進行初始化.

You could alternatively use new to create an instance of Long, initializing it with the int value.

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