Java 从 Object 到 long 到 String 的转换
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Java Cast from Object to long to String
提问by Mastergeek
Here's the situation, I have an Object in a Map which I explicitly know to contain an instance of Long and I need to turn that value into a string but keep getting incompatible type errors. Here's what my code looks like:
这是这种情况，我在 Map 中有一个对象，我明确知道它包含一个 Long 的实例，我需要将该值转换为字符串，但不断收到不兼容的类型错误。这是我的代码的样子：
Map<String, Object> map = ...;
Object obj = new Long(31415L);
String str = Long.valueOf((long)map.get("id")); //Problem line
This gives:
这给出：
Inconvertible types.
Found : java.lang.Object
Required: long
Any suggestions as to how to get around this?
关于如何解决这个问题的任何建议？
回答by fge
Use, for instance:
使用，例如：
String.valueOf(map.get("id"))
The problem is that you try and cast an object to a primitive type. That cannot work.
问题在于您尝试将对象强制转换为原始类型。那行不通。
But since the values of your map will be Longs anyway (collections cannot contain primitive types, save for specialized implementations such as found in GNU Trove), look at @BheshGurung's answer...
但是由于您的地图的值Long无论如何都是s（集合不能包含原始类型，除了在 GNU Trove 中找到的特殊实现之外），请查看@BheshGurung 的答案...
回答by Bhesh Gurung
You can just do
你可以做
String str = map.get("id").toString();
回答by zee
You can use the toString function;
public String toString() {
return String.valueOf(map.get("id"))
}
String str = map.get("id").toString();
回答by technophiliac
You have 2 issues here:
你在这里有两个问题：
You created a *L*ong, not a *l*ong. Therefore you need to cast back to a *L*ong, not a *l*ong.
In order to get the String representation of a *L*ong you must call toString() on it.
您创建了 * L*ong，而不是 * l*ong。因此，您需要转换回 * L*ong，而不是 * l*ong。
为了获得 * L*ong的字符串表示，您必须对其调用 toString() 。
Use this:
String str = ((Long)map.get("id")).toString();
用这个：
String str = ((Long)map.get("id")).toString();
