Newb to Declaring Variables - Wanna help?

Question

Hi everyone, yep, this is a total newb question, I've "RTFM" but I still don't understand, concepts like this just don't exist in the languages I'm used to programming. Anyway, my question is simple: how does one properly set a global variable which can be used by all public void functions inside that class?

Here is some example code, I will highlight the redundancy in case you don't see it:

public class baketimer extends Activity implements OnClickListener {
    /** Called when the activity is first created. */

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        final Button cupcake1 = (Button) this.findViewById(R.id.cupcake1);

        cupcake1.setOnClickListener(this);        
    }

    public void onClick(View v) {
        switch(v.getId()){
        case R.id.cupcake1:
            final Button cupcake1 = (Button) this.findViewById(R.id.cupcake1);
            new CountDownTimer(30000, 1000) {

                public void onTick(long millisUntilFinished) {
                    cupcake1.setText("" + millisUntilFinished / 1000);
                }

                public void onFinish() {
                    cupcake1.setText("Done!");
                }
            }.start();
            Toast.makeText(this, "Mmm cupcakes!", Toast.LENGTH_SHORT).show();
            break;

How would I go about declaring cupcake1 for the entire class? I know, this must be so newb, why I can't find it, I dunno.

Thanks in advance!

Answer 1

For the entire class, you define it as static inside the class but outside any function, such as:

public class testprog {
    static int xyz = 0;
    public static void main(String args[]) {
    }
}

But make sure that's what you want. That one single variable will be shared amongst all instances of your class and you'll probably have to synchronise access to it if you're using threads. If you want something that's available to all functions in your class but still has one per instance, leave off the static.

Answer 2

declare the variable inside the class and outside any function, but not necessarily static.

public class YourClass{
    Button cupcake = null;
    public void onCreate(Bundle savedInstanceState) {
        ...
        cupcake = (Button) this.findViewById(R.id.cupcake1);
        ...
    }
    public void onClick(Bundle savedInstanceState) {
        ...
    }
}

Use static (static Button cupcake = ...) if you want the variable to be shared by ALL objects in your program. Otherwise, don't use static, so that the variable only belongs to that object.

Answer 3

First we need to be clear what you mean by "global variable".

• Java has static variables that are shared by all instances of a class.
• Java has instance variables that belong to a single instance of a class.
• Java has local variables and parameters that exist while some method (or code block) is executing.
• Java does not have global variables in the sense of C/C++.

Having said that, here's a simple example that declares a static and an instance variable.

public Foo {
   private static int fooCounter;
   private int nosLegs;

   public Foo (int n) {
       nosLegs = n;
       fooCounter++;
   }

   /* There is only one counter of Foo instances created */
   public static int getFooCount() {
       return fooCounter;
   }

   /* Each Foo can have a different number of legs */
   public int getNosLegs() {
       return nosLegs;
   }
}