import java.util.HashSet;public class JPTQuestion3 {public static void main(String[] args) {HashSet shortSet = new HashSet();for (short i = 0; i < 100; i++) {shortSet.add(i);shortSet.remove(i - 1);}System.out.println(shortSet.size());} }

輸出:100。

如果把循環(huán)變量改為int型的, 那么

import java.util.HashSet;public class JPTQuestion3 {public static void main(String[] args) {HashSet shortSet = new HashSet();for (int i = 0; i < 100; i++) {shortSet.add(i);shortSet.remove(i-1);}System.out.println(shortSet.size());} }

輸出:1

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這是什么坑啊。而且，這HashSet竟然不指定泛型就在用了-_-

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為什么范圍比int小的的就不會(huì)被移除，而大于等于int范圍的就會(huì)被移除？泛型指定與否都與結(jié)果無(wú)關(guān)。

?

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原因：.........................................i-1是int型的，HashSet里面存的是Short類型的，所以，沒(méi)有一個(gè)數(shù)字被移除。

官方解釋：自動(dòng)裝箱的作用

Java Programming Test Question 3 Answer and Explanation

The size of the shortSet will be 100. Java Autoboxing feature has been introduced in JDK 5, so while adding the short to HashSet<Short> it will automatically convert it to Short object. Now i-1 will be converted to int while evaluation and after that it will autoboxed to Integer object but there are no Integer object in the HashSet, so it will not remove anything from the HashSet and finally its size will be 100.

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轉(zhuǎn)載于:https://www.cnblogs.com/fuzhihong0917/p/5703678.html

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