检查Object的错误是null

Question

I got a HttpResponse which gets a json response.

Now if the json response contains data it all works fine, but whenever the json is null my application crashes.

I've been trying to following code but with no avail.

(sb = json response)

Object result11 = sb;
Log.d("Result11", result11.toString());

if (result11 == JSONObject.NULL)
    Log.d("if", "I am NULL");
else
    Log.d("else", "I am not null");

I tried comparing result11 to:

null, "", "null", JSONObject.NULL

It always returns "I am not null"

Whilst the log says that Resul11 = null.

Any help would be appreciated. Thanks in advance.

EDIT:

Object result11 = sb;
            Log.d("Result11", result11.toString());

            StringBuilder test = (StringBuilder)result11;

            if (test.toString().equals("null"))
                Log.d("if", "I am NULL");
            else
                Log.d("else", "I am not null");

SOLUTION by @Mark Byers

test.toString().trim().equals("null") 

results in "I AM NULL"

Answer 1

You don't have a null . You have a StringBuilder that when converted to a String contains the value "null" .

To compare strings do not use the == operator. Instead you should convert to a String and use the equals method.

StringBuilder stringBuilder = (StringBuilder)result11;
String trimmed = stringBuilder.toString().trim();
if (trimmed.equals("null")) { ... }

The == operator compares the references and only returns true if the operands are references to the same object (or both null references). The equals method compares the values.

Related

• Java String.equals versus ==

Answer 2

如果你得到一个null结果与空指针比较： result11 == null