将整数插入 TreeMap
我想存储项目的 ID 及其相应的坐标。为此，我使用 TreeMap，其中坐标是包含 int x 和 int y 的类。现在，为了将数据插入到地图中，我可以写：
treeMapObject.put(5,new BasicRow(30,90));
或者我必须写：
treeMapObject.put(new Integer(5),new BasicRow(30,90));
我猜只有第二个是正确的，因为地图处理对象。但现在的问题是，假设我有以下代码：
treeMapObject.put(new Integer(5),new BasicRow(30,90));
treeMapObject.put(new Integer(5),new BasicRow(45,85));
在这种情况下会发生什么？
I want to store the IDs of items and their corresponding co-ordinates. For this, I'm using a TreeMap where Coordinates is a class containing int x and int y. Now, for inserting data into the map can I write:
treeMapObject.put(5,new BasicRow(30,90));
Or do I have to write:
treeMapObject.put(new Integer(5),new BasicRow(30,90));
I guess only the second one is correct because Maps deal with objects. But now the question is, say I have the following piece of code:
treeMapObject.put(new Integer(5),new BasicRow(30,90));
treeMapObject.put(new Integer(5),new BasicRow(45,85));
In such a case what will happen?
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评论（3）
实际上这两个版本都是正确的，因为你的Java编译器将为你执行所谓的“自动装箱”：如果你提供一个int，而需要一个Integer，java会自动为你将该int包装在一个Integer对象中。反之亦然（已在 Java 5 中引入。如果您使用甚至不应该编译的旧 Java 版本）。
对于您的第二个问题：您首先添加的条目将被覆盖。
actually both versions are correct, because your Java compiler will perform what is called "autoboxing" for you: If you supply an int, where an Integer is required, java will automatically wrap that int in an Integer object for you. This works vice-versa as well (has been introduced in Java 5. If you'd use an older Java version that should not even compile.).
For your second question: The entry you added first will be overwritten.
yankee 是对的，两者都可以工作，因为 Java 将 autobox< /a> 将整数值转换为
Integer对象。请注意，如果您想显式执行此操作，最好编写：
而不是：
如果您使用
valueOf，则类Integer可以避免创建新的Integer对象，它将从其内部缓存中返回一个预先存在的Integer对象，这比创建新对象更有效。yankee is right, both will work, because Java will autobox the integer values into an
Integerobject.Note that if you want to do this explicitly, it is better to write:
instead of:
If you use
valueOf, then classIntegercan avoid creating a newIntegerobject, it will return a pre-existingIntegerobject from its internal cache, which is more efficient than creating a new object.存在轻微差异，但不会影响地图的行为。在这两种情况下，如果您尝试获取整数 5 的值，映射将返回该基本行。
区别：第二行总是创建一个新的 Integer 实例，而第一行可能会插入一个现有实例。但地图是通过平等进行比较，而不是身份，所以这实际上并不重要。只是第一行对内存消耗有（非常）小的积极影响。
There is a slight difference, which does not affect the behaviour of the map. In both cases, if you try to get the value for integer 5, the map will return that basic row.
The difference: the second line will always create a new instance of
Integerwhile the first one may insert an existing instance. But maps compare by equality, not by identity, so it actually doesn't matter. Just that the first line has a (very) small postive impact on memory consumption.