Java 为什么我会收到“不兼容的类型：对象无法转换为字符串”？
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Why am I getting, "incompatible types: Object cannot be converted to String" with this?
提问by B. Clay Shannon
I'm trying to use the simplest possible code for calling a Web API REST method from an Android app, and the code that I found herelooked very promising:
我正在尝试使用最简单的代码从 Android 应用程序调用 Web API REST 方法，我在这里找到的代码看起来非常有前途：
public String callWebService(String requestUrl)
{
String deviceId = "Android Device";
HttpClient httpclient = new DefaultHttpClient();
HttpGet request = new HttpGet(requestUrl);
request.addHeader("deviceId", deviceId);
ResponseHandler handler = new BasicResponseHandler();
String result = "";
try
{
result = httpclient.execute(request, handler); // <= a line too far
}
catch (ClientProtocolException e)
{
e.printStackTrace();
}
catch (IOException e)
{
e.printStackTrace();
}
httpclient.getConnectionManager().shutdown();
return result;
}
However, it won't compile, telling me: "incompatible types: Object cannot be converted to String" on this line:
但是，它不会编译，在这一行告诉我：“不兼容的类型：对象无法转换为字符串”：
result = httpclient.execute(request, handler);
It does give a couple of options in an attempt to circumvent the logjam:
它确实提供了几个选项来试图绕过僵局：
...but I don't know which, if any, of these options is the preferred way to solve this dilemma. Is one way "the way"?
...但我不知道这些选项中的哪一个（如果有的话）是解决这个困境的首选方法。一种方式是“方式”吗？
UPDATE
更新
This code, as I said, looks promising to me, however I think it's basically unusable as is, because it gives me the dreaded "NetworkOnMainThreadException" From logcat:
正如我所说，这段代码对我来说看起来很有希望，但是我认为它基本上无法使用，因为它给了我可怕的“ NetworkOnMainThreadException”来自 logcat：
04-01 13:18:41.861 1267-1267/hhs.app E/AndroidRuntime﹕ FATAL EXCEPTION: main
. . .
java.lang.IllegalStateException: Could not execute method of the activity
. . .
Caused by: java.lang.reflect.InvocationTargetException
. . .
Caused by: android.os.NetworkOnMainThreadException
采纳答案by Sotirios Delimanolis
Because you are using a raw type in
因为您使用的是原始类型
ResponseHandler handler = ...
With raw types, the type variables in the method declarations are erased. So everything appears as Object(or whatever the leftmost bound of the type parameter is).
对于原始类型，方法声明中的类型变量将被删除。所以一切都显示为Object（或任何类型参数最左边的边界）。
Instead, use a parameterized type
相反，使用参数化类型
ResponseHandler<String> handler = ...
This also works because BasicResponseHandlerextends ResponseHandler<String>.
这也有效，因为BasicResponseHandlerextends ResponseHandler<String>。
Now
现在
httpclient.execute(request, handler);
will have a return type associated with the type argument used when declaring handler, which is Stringand the result can therefore be assigned to a Stringvariable (or anywhere a Stringis expected).
将具有与声明时使用的类型参数关联的返回类型handler，String因此可以将结果分配给String变量（或String预期的任何地方）。
回答by Ivan Verges
Try this:
尝试这个：
result = httpclient.execute(request, handler).toString();
If i'm not wrong, you should be able to use the "toString" method to convert the return of execute method to String type.
如果我没猜错，您应该可以使用“toString”方法将 execute 方法的返回值转换为 String 类型。
