NullPointerException... god damn it! (java)

[bobthe2lol]

I'm getting a null pointer exception, and i have no idea why. There really isnt much more to say about this, so here.

Error:

Exception in thread "main" java.lang.NullPointerException
at java.nio.HeapByteBuffer.get(HeapByteBuffer.java:143)
        at ClientNetwork.WranglePacket(ClientNetwork.java:50)
        at ClientNetwork.ExtractPacket(ClientNetwork.java:35)
        at ClientNetwork.Read(ClientNetwork.java:25)
        at Client.run(Client.java:29)
        at java.lang.Thread.run(Thread.java:636)
        at Server.ListenForConnection(Server.java:28)
        at Server.<init>(Server.java:13)
        at Server.main(Server.java:34)

And the class file that is causing it:
It starts in WranglePacket here:

case 0x02:
                short Length = inbuffer.getShort();
                System.out.println("Got a length: "+Length+","+inbuffer.position());
                if(Length>0){
                    byte[] str = null;
                    inbuffer.get(str, 0, Length); //line 50
                    String string = new String(str,"UTF8");
                    System.out.println("Aha! Got a username: "+string);
                    username = string;
                } else{
                    System.out.println("False alarm!");
                }

The rest of the file:

import java.io.*;
import java.net.*;
import java.nio.ByteBuffer;
public class ClientNetwork{
    Socket sock;
    int ID;
    String username;
    ByteBuffer inbuffer;
    ByteBuffer outbuffer;
    ClientNetwork(Socket soc, int id){
        sock = soc;
        ID = id;
        inbuffer = ByteBuffer.allocate(4096);
        outbuffer = ByteBuffer.allocate(4096);
        InitPackets();
    }

    public void InitPackets(){
        new Handshake();
    }

    public void Read(byte[] data) throws UnsupportedEncodingException{
        inbuffer.put(data);
        System.out.println("Reading in "+data.length+" bytes of data.");
        ExtractPacket();
    }

    public void ExtractPacket() throws UnsupportedEncodingException{
        int Position =  inbuffer.position();
        inbuffer.position(0);
        byte i;
        while((i = inbuffer.get())!=0){
            System.out.println(i);
            if(Packets.IsPacket(i)){
                WranglePacket(i);
            }
        }
        inbuffer.position(Position);
    }

    public void WranglePacket(int ID) throws UnsupportedEncodingException{
        System.out.println("Whoopee! Wrangling!");
        inbuffer.position(1);
        switch (ID){
            case 0x02:
                short Length = inbuffer.getShort();
                System.out.println("Got a length: "+Length+","+inbuffer.position());
                if(Length>0){
                    byte[] str = null;
                    inbuffer.get(str, 0, Length);
                    String string = new String(str,"UTF8");
                    System.out.println("Aha! Got a username: "+string);
                    username = string;
                } else{
                    System.out.println("False alarm!");
                }
            default:
                System.out.println("Unknown ID: "+ID);
        }
    }
    

}

If you can see the error, that would be great. I can't :P
Thanks in advance!

[Smashmaster]

Which line is line 50 in WranglePacket

Wait

byte[] str = null;
inbuffer.get(str, 0, Length); //line 50

I'm guessing it's that one.

Assign str before you use it.

[VoiDeD]

byte[] str = null;
inbuffer.get(str, 0, Length); //line 50

The issue is that str isn't initialized, and is null.

You'd need to create a byte array of size Length there.

[url][noparse]http://download.oracle.com/javase/1.4.2/docs/api/java/nio/ByteBuffer.html#get%28byte[],%20int,%20int%29[/noparse][/url]

[quote]
In other words, an invocation of this method of the form src.get(dst, off, len) has exactly the same effect as the loop

for (int i = off; i < off + len; i++)
dst[i] = src.get();
[/quote]

[bobthe2lol]

Ah, great. Thank you very much.

Got a length: 10
Aha! Got a username: bobthe2lol

Works perfectly :)

I have another question aswell, if possible. How can I get the number of elements in a ByteBuffer? There seems to be no function to do this, and buffer.array().length just returns the length that i allocated it with...?

[jA_cOp]

[QUOTE=bobthe2lol;27433446]
I have another question aswell, if possible. How can I get the number of elements in a ByteBuffer? There seems to be no function to do this, and buffer.array().length just returns the length that i allocated it with...?[/QUOTE]

arrayOffset() could be it.

[bobthe2lol]

Thanks. I gave up on ByteBuffer and wrote my own wrapper for byte with all the write and read functions etc. I may be an idiot, and was using the wrong thing in the first place, but oh well :v:

[jA_cOp]

[QUOTE=bobthe2lol;27439276]Thanks. I gave up on ByteBuffer and wrote my own wrapper for byte with all the write and read functions etc. I may be an idiot, and was using the wrong thing in the first place, but oh well :v:[/QUOTE]

As long as you know what a terrible, terrible idea that is :v:

[bobthe2lol]

Why so? It's simple really. It has a byte[] in it, and then it has write/read byte/int/short/long/string etc. Why is it a bad idea?

[jA_cOp]

[QUOTE=bobthe2lol;27439368]Why so? It's simple really. It has a byte[] in it, and then it has write/read byte/int/short/long/string etc. Why is it a bad idea?[/QUOTE]

The best code you'll ever write is code you never have to write.

[bobthe2lol]

True, so can you point me to a byte[] wrapper that has function to write and read string/byte/byte[]/int/long/short/etc that is already written?

[jA_cOp]

[QUOTE=bobthe2lol;27439797]True, so can you point me to a byte[] wrapper that has function to write and read string/byte/byte[]/int/long/short/etc that is already written?[/QUOTE]

[url=http://download.oracle.com/javase/1.4.2/docs/api/java/nio/ByteBuffer.html]ByteBuffer[/url]?

(As for Strings - convert them to byte arrays or byte buffers first (e.g. String.getBytes()). Remember that there are many different ways to encode a string.)