instanceof不适用于“或”

Question

I'm working on a web project with Java.

My colleague has finished the socket part, including object serialization and deserialization.

What I need to do is to develop the classes that would be serialized and deserialized to send and receive them.

The sequence diagram is simple:

• the client sends a string to the server
• the server create an object with the received string
• the server sends the object to the client

I have now two kinds of objects:

class T1{public int i1 = 1;}
class T2{public int i2 = 2;}
//both classes have implemented Serializable and override toString

And I do things as below:

Object obj = class.forName(strFromClient).newInstance();
if(obj instanceof T1 || obj instanceof T2)
{
    // send obj to client with my colleague's method
    send(obj);
}

The client can receive successfully the obj of type of T1 , the client can System.out.println(obj) and get 1 .
To my surprise, when I do the same thing for T2 , it doesn't work. When the client try to System.out.println(obj) , a 0 is shown whereas I'm expecting a 2 . I also try to add a String into T2 and the client get an NullException , meaning that the string in the received obj is null .

I don't quite understand why but if I change my code like this, everything will be fine:

Object obj = class.forName(strFromClient).newInstance();
if(obj instanceof T1)
{
    // send obj to client with my colleague's method
    send(obj);
}
else if(obj instanceof T2)
{
    // send obj to client with my colleague's method
    send(obj);
}

Answer 1

I did a test using the following code:

Object x = 1; // afterwards = ""

if (x instanceof String || x instanceof Integer) {
    System.out.println("Hurray!");
}

In both cases: x = 1 or x = "" the string Hurray! was printed. Hence I guess your obj is neither of type T1 nor of type T2 .

Answer 2

i think your problem is - T1 and T2 value you receive there are null ,

in only that case the condition will not get validated .

Please debug and check the value of T1 and T2 you receive in the step.

You can use this code - and add null checks before instance of