Java - Duplicate methods in classes and how to call them from another class

Question

I am learning and loving Java and Android but have a long way to go. This is a best practice question, I think. In my Android Activity I have 6 classes. Several of them are calling methods that I have duplicated from another class. It seems redundant to duplicate the methods when I could just call them from another class. I also think it would be easier to maintain them all in one class. (Main activity, maybe?) My question is: What is the best practice for calling the same method from more than one class? For example, say my classes are:

Main Activity GameSelector Game1Home Game1

I have a few methods which are the same in every class. Lets call them getPrefs() and setPrefs(). I am not passing anything into them or out of them. Which class should they go in, and how do I call them from another class?

Edit - Thanks to some very helpful answers I have a fully functioning Configurations class and my other 6 classes look much cleaner! This will be very easy to maintain and I learn a few great pointers while making it. I'm posting my finished class here in case it may help anyone else. You can call the methods from your other classes like this:

Configurations.getPrefs(this);

and refer to static variables you've defined as global in your configurations file like this:

Configurations.buttonClicked.start();

Configurations.java:

public class Configurations extends Activity {
static MediaPlayer buttonClicked;
static MediaPlayer instructionsAudio;
static MediaPlayer messageAudio;
static MediaPlayer correctNum_sound;
static MediaPlayer incNuma_sound;
static MediaPlayer incNumb_sound;
static String storeChildsName;
static String storeRequestedRange;
static String storeVoiceChoice;
static Intent i;


public static void setupPrefs(final Activity a) {
    ImageButton settingsClicked = ((ImageButton) a.findViewById(R.id.prefButton));
    settingsClicked.setOnClickListener(new OnClickListener() {

            public void onClick(View v) {
                ImageView settingsClicked = ((ImageView) a.findViewById(R.id.prefButton));
                    settingsClicked.setImageResource(R.drawable.settings_button_clicked);
                buttonClicked = MediaPlayer.create(a, R.raw.click);
                    buttonClicked.start();

                    Intent settingsActivity = new Intent(a.getBaseContext(),
                                    Preferences.class);
                    a.startActivity(settingsActivity);
            }
    });
}
public static void getPrefs(final Activity a) {
    // Get the xml/preferences.xml preferences
    SharedPreferences prefs = PreferenceManager
                    .getDefaultSharedPreferences(a.getBaseContext());
    storeChildsName = prefs.getString("editTextPref",
                    "Friend");
    storeRequestedRange = prefs.getString("listPref", "3");
    storeVoiceChoice = prefs.getString("voices", "1");
}

public static void setupMusicToggle(final Activity a) {
    i=new Intent(a, MyMusicService.class);
       final ToggleButton togglebutton =(ToggleButton)a.findViewById(R.id.music_toggle);
      togglebutton.setOnClickListener(new OnClickListener() {  
          public void onClick(View v) {   
              // Perform action on clicks    
              if (togglebutton.isChecked()) {   
                  Toast.makeText(a, "Music on.", Toast.LENGTH_SHORT).show();  
                  a.startService(i);  
              } else {   
                  a.stopService(i);
                  Toast.makeText(a, "Music off.", Toast.LENGTH_SHORT).show(); 
                      }    }}); 
}

public static void returnHome(View view, Activity a) {
    ImageView homeClicked = (ImageView) a.findViewById(R.id.home);
    homeClicked.setImageResource(R.drawable.homebuttonclicked);
    buttonClicked = MediaPlayer.create(a, R.raw.click);
    buttonClicked.start();
    Intent intent = new Intent(a, GameSelector.class);
    a.startActivity(intent);
}

public static void releaseMP(Activity a) {
    if (buttonClicked != null) {
        buttonClicked.stop();
        buttonClicked.release();}
        if (instructionsAudio != null) {
            instructionsAudio.stop();
            instructionsAudio.release();}
        if (messageAudio != null) {
            messageAudio.stop();
            messageAudio.release();
        }
        if (correctNum_sound != null){
            correctNum_sound.stop();
            correctNum_sound.release();
        }
        if (incNuma_sound != null) {
            incNumb_sound.stop();
            incNuma_sound.release();
        }
        if (incNumb_sound !=null) {
            incNumb_sound.stop();
            incNumb_sound.release();
        }
}

public static boolean isMyServiceRunning(Activity a) {
    ActivityManager manager = (ActivityManager) a.getSystemService(Context.ACTIVITY_SERVICE);
    for (RunningServiceInfo service : manager.getRunningServices(Integer.MAX_VALUE)) {
        if (MyMusicService.class.getName().equals(service.service.getClassName())) {
            return true;
        }
    }
    return false;
}

}

Hope this helps someone as much as it's helped me!

PS - If you see any room for improvement in this code please share! I have a lot to learn =)

Answer 1

What I do is to create an abstract Activity class that extends the Android API's Activity class (or the support library's FragmentActivity class):

public abstract class Activity extends android.app.Activity { //or extends FragmentActivity
//put your common stuff here
}

Similar recommendations would ask you to name this class BaseActivity, but I like the name Activity better because it's in sync with the Android system.

All my activities would be extended from this abstract class:

//GameActivity.java
public class GameActivity extends Activity {
}

//OptionsActivity.java
public class OptionsActivity extends Activity {
}

I also keep this abstract Activity class (and some other goodies) in a library project so that I have a single base for all my common stuff and all my other projects would simply include this as a library (Project Properties > Android > Libraries > Add). But of course, your development needs may differ from this model.

Extra tips for your Java development:

• Always start with the strictest access modifier (private), changing to more leniant ones as you need more access (default > protected > public).
• If a method does not use anything non-static, be sure to make it a static method. This way you don't have to instantiate an object just to call the method inside its class.
• Use getters and setters for member fields unless you are sure direct access is desired and will not introduce chances of errors.
• Use wrapper classes like java.lang.Integer when you need to show 'not known' or 'invalid' status of a primitive type (int).

Answer 2

It all depends upon the sole purpose of the classes and methods you define.

If there are too many methods you need to use in many of your activities, then one option wil be;

1. Define a separate helper class and implement those methods there. Include them in all your required classes.
2. Inheritance or interface would be a second option.

Answer 3

There are several ways to share code - you can do it by

1. Defining a "helper" class, and adding your static methods to it,
2. Defining a base class (often an abstract base class) and adding your methods to it,
3. Defining a non-static class, and embedding an instance of that class in each of the classes that need to share the code; classes could also share a reference to a common instance.

It is hard to say which approach is more appropriate, but from the method names it appears that you are planning to get and set preferences. In situations like that, the #1 or #3 with a shared instance are often the most appropriate.

Answer 4

It depends on what each method does. By the name, getPrefs() looks like setting preferences of some sort. In that case, what I personally do, is create a class Configuration and make a singleton instance that all classes share.

Android is slightly different from the usual Java.
In 'usual' Java, you instantiate the objects, have a reference to them and then you call methods on them.
In Android, most of your methods are defined in Activity, Fragment, DialogFragment , etc. and you are not in control of instantiating them. The methods defined whitin those can only be called within themselves unless declared static.

So, go over your design, see what the methods do and check if you can make a different class out of them :)
Hope it helps.