How to properly synchronize Threads/Classes

[djdanjo82]

Hello All! Thank you very much for viewing this thread. My problem is I am trying to pass a number value between classes/thread of the same java project in eclipse. I have a java project of 9 classes with three threads. The Display Class/Thread needs to accept a value coming from the Tcpdump Class/Thread. When both of these are ran separately everything is fine. But when I try to pass the count value in Tcpdump it does not function correctly. It either does not get the value or it does not update the right value. It is strange. I am trying to understand synchronizing since I think that is my solution however I do not really know where to begin. I have posted the Tcpdump class below.
__________________________________________________
import java.io.IOException;
import jpcap.*;
import jpcap.packet.Packet;

public class Tcpdump extends Thread implements PacketReceiver{

static int index = 1;
public int received_packets;
//int count = 0;
public int count;
public int packetPSecond;
private Main classMain;
public int tcpdumpSecondCount;
NetworkInterface[] devices = JpcapCaptor.getDeviceList();

public Tcpdump(Main projectMain){
System.out.println("Tcpdump.Tcpdump()");
this.classMain = projectMain;
}

public void receivePacket(Packet packet) {
System.out.println("THIS IS THE PACKET NUMBER: " + " - " + packet);
countPackets();
}

public void countPackets() {
this.count = this.count + 1;
System.out.println("This is the value of count: " + count);

//This line passes count--which is the (Total Number of packets)
classMain.display.gettcpDumpPacketCount(count);
}

public void openDevice() {
System.out.println("This is Tcpdump Opendeive...packets should be captured now");
NetworkInterface[] devices = JpcapCaptor.getDeviceList();
JpcapCaptor jpcap = null;
System.out.println("usage: java Tcpdump <select a number from the following>");
try {
jpcap = JpcapCaptor.openDevice(devices[0], 2000, false, 1000);
//jpcap = JpcapCaptor.openDevice(devices[1], 2000, false, 1000);
} catch (IOException e) {

e.printStackTrace();
}

jpcap.loopPacket(-1, new Tcpdump(classMain));
jpcap.close();
}

public void run() {
System.out.println("Tcpdump is on--------------------------!!!");
openDevice();
}

public void main() throws Exception {
System.out.println("This is Tcpdump main, openDevice should start:");

}
}
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The display class---this method I am using to accept the value is
public Display{

...

public void gettcpDumpPacketCount(int count){
System.out.println("THis is count at display: " + count);
dumpPacketCount = count;
}
}
__________________________________________________ __
Both classes and threads are initialized in my main class.

I would appreciate any advice you could give me. Thanks a lot.

Dan

[kvprajapati]

First thing - Your source code must be surrounded by the bb code tags. See # icon at toolbar or read this How to use BB code tags?

There are two methods for synchronization:
1. Object lock
2. Class lock

Use synchronized keyword to qualify a method or a block.

[djdanjo82]

Thanks adatapost for your reply. I think I may have solved my problem. However, it almost seems too easy. I just added the synchronized word to my method that delivers the long value to my other class/method that is apart of another thread. I know this solution is not very efficient but it might work. I will plan on testing this tomorrow with wireshark. I am basically trying to build my own network analyzer.

public synchronized void countPackets() {
    this.count = this.count + 1;
    //while(classMain.display.network == false)
    System.out.println("This is the value of count: " + count);

        classMain.display.gettcpDumpPacketCount(count);
    }

Thanks again!
Dan