Array of classes in JAVA (using it as a struct)

Question

I have a question about how to make an array of classes. My background is in embedded C, so Java is a bit new for me.

In C you could make a struct. In java I found that this is not possible, so I created a class:

public class Message
{
    public String Text;
    public enum Type {warning,caution,advisory,engineering};
    public enum Actions {yes,no};
    public int priority;

    public Message(String Text,Type nType,Actions nActions,int priority)
    {
         this.Text = Text;
         type = nType;
         actions = nActions;
        this.priority = priority;
    }
    private Type type;
    private Actions actions;

    public String getText() { return Text; }
    public void setText(String Text) { this.Text = Text; }
}

So I kind of used this as a "struct" (in C).

I would like to make an array of this class.

What I did in the main:

public class Main extends AppCompatActivity 
{

SurfaceView cameraView;
TextView textView;
CameraSource cameraSource;
final int RequestCameraPermissionID = 1001;

Message[] dbmessage;
dbmessage = new Message[300];
dbmessage[0] = new Message("TEST MESSAGE", Message.Type.warning,Message.Actions.no,1);

}

WHAT I SHOULD HAVE DONE IN THE MAIN: (BEST ANSWER)

public class Main extends AppCompatActivity 
{
SurfaceView cameraView;
TextView textView;
CameraSource cameraSource;
final int RequestCameraPermissionID = 1001;

// you have to put it into a method. 
public void myMethod() {
    Message[] dbmessage;
    dbmessage = new Message[300];
    dbmessage[0] = new Message("TEST MESSAGE",  Message.Type.warning,Message.Actions.no,1);
}

}

The compiler shows an error: "unknown class dbmessage" I think it is mainly a syntax error?

Would any of you be able to shine a light on this, or give me a kick in the good direction?

Please be patient with me, as Java(or even programming) is not my profession and I am just trying to learn.

EDIT: Thanks to multiple members pointing out that I used code outside a method. This is the solution(obviously). The code from the MAIN is now placed in a method and works perfect. Thank you guys for the patience and the help!

Answer 1

If the code you gave us from class Main is complete (it can't be, because the imports are missing), you try to write statements outside of a method. That's not allowed in Java syntax. A correct snippet would be:

public class Main extends AppCompatActivity 
{
    SurfaceView cameraView;
    TextView textView;
    CameraSource cameraSource;
    final int RequestCameraPermissionID = 1001;

    // you have to put it into a method. 
    public void myMethod() {
        Message[] dbmessage;
        dbmessage = new Message[300];
        dbmessage[0] = new Message("TEST MESSAGE",  Message.Type.warning,Message.Actions.no,1);
    }
}

I'd recommend to get good tutorials / textbooks on both Java as well as Android programming. Otherwise it will be a frustrating experience. Surely there will be chapters on the Java style guide, among others.

Answer 2

Check this post for array of class instanciation.

Although I would recommand you to use an ArrayList, which are kinda similar to vector in C++.

List<Message> myList = new ArrayList<Message>();
myList.add(new Message("TEST MESSAGE", Message.Type.warning,Message.Actions.no,1));

Answer 3

Your problem is that you are refering a non-static variable in a static context. What you need to do is something along the lines of: Create an instance of the mainclass, Create a non-static void that does what you want Call that void from the class instance: This works for me:

class Program
{
    public static void main (String[] args)
    {
        Program p = new Program();
        p.Run();
    }

    public void Run()
    {
        Message[] array = new Message[300];
        array[0] = new Message("TEST MESSAGE", Message.Type.warning,Message.Actions.no,1);
    }
}