How to access same instance of object in multiple classes

[Josh Reev]

If i create an object in Class1 and save some data in that object in Class1, how can i access that same data in Class2? Here's a code sample that should clarify my situatuation:

Class1.java:

public class Class1 implements Runnable {
 	public ClientArray ca;

    	public Class1(int port) throws IOException {
        ca = new ClientArray();
	Client client = new Client(socket);
	ca.setArraySize();
 	ca.addClient(client);
    }

Class2.java:

    protected void doInSession() {

        
	//need to access that same ClientArray ca here that i created in Class1!
        System.out.println(ca.getClient() + "clietttttttttttttt");
    }


ClientArray.java:

public class ClientArray {
    Client[] ClientArray;

    public void ClientArray() {
    }

    public void setArraySize() {
        System.out.println("new ca");
        ClientArray = new Client[100];
    }
    
    
    public void addClient(Client client) {
        ClientArray[0] = client;
        
    }
    public Client getClient() {
        System.out.println(ClientArray[0].getSocket() + " aaaaaaaaaaaaaaaaaa");
        return ClientArray[0];
    }
    
}

[William P O'Sullivan]

In Class2 you need to access Class1's property (in your case ca)

Either declare ca as public and use class1.ca or use the proper get/set pattern.

To access Class1 from any other class, you need a Singleton(static) instance.

WP

[Steve Luke]

The best way to do that is to pass the Object from one class to another. So if you make an instance of Class2 inside Class1, you might do this:

class Class1
{
    //...

        Class2 class2Instance = new Class2(this.ca);
    //...
}

clas Class2
{
    private final ClientArray ca;

    public Class2(ClientArray cArray)
    {
        this.ca = cArray;
    }

    //...
}

If Class1 doesn't know about Class2, but Class2 knows about Class1 then you can use a getter method:

class Class1
{
     private ClientArray ca;

    public ClientArray getClientArray()
    {
        return this.ca;
    }
}

If Class1 doesn't know about Class2 and Class2 doesn't know about Class1, then there needs to be some controller class which knows about both. Class1 would allow others to get the ClientArray, and Class2 would be assigned the ClientArray:

class Class2
{
    private ClientArray ca;

    public void setClientArray(ClientArray cArray)
    {
        this.ca = cArray;
    }
}

class SomeController
{
    //...
        Class1 class1Instance = //...
        Class2 class2Instance = //...
        class2Instance.setClientArra( class1Instance.getClientArray() );
    //...
}

Finally, if Class1 doesn't know about Class2, and Class2 doesn't know about Class1, and there is no Controller type thing which both know about, then there needs to be some shared Scope object to hold the value. Class1 would pass the value to the Scope and Class2 would take the value from the Scope.

class Scope
{
    private ClientArray ca;

    public ClientArray getClientArray()
    {
        return this.ca;
    }

    public void setClientArray(ClientArray cArray)
    {
        this.ca = cArray;
    }
}

class Class1
{
    private final Scope scope;

    public Class1(Scope scope, int port)
    {
        this.scope = scope;

        ClientArray ca = new ClientArray();
        Client client = new Client(port);
        ca.setArraySize();
        ca.addClient(client);

        this.scope.setClientArray(ca);
    }
}

class Class2
{
    private final Scope scope;

    public Class2(Scope scope)
    {
        this.scope = scope;
    }

    protected void doInSession()
    {
        ClientArray ca = this.scope.getClientArray();
        System.out.println(ca.getClient() + "clietttttttttttttt");
    }
}

[Josh Reev]

Thanks for your efforts, it looks like i can achieve what i want by creating ClientArray like this:

       ca = ClientArray.getInstance();

and getInstance looks like this:

   public static ClientArray getInstance() {
                if (instance==null)
                  instance = new ClientArray();
        return instance;
    }

[Steve Luke]

Before you get into using a Singleton for this, I would suggest you take a search around forum (or the net in general) on the proper use of Singletons. It can be debated as to what the appropriate use of them are, but there are good discussions about whether to use them 'because they are easier' as opposed to some other approach which may be more resilient and Object-Oriented friendly.

For example: this recent thread has a pretty good discussion on the subject. And it also has some great links that describe the things to consider in great detail.