Question

may be its too simple but I couldnt find the right way.

In C++ I can write initWithParameter: xxx to instantiate a class and then in the init set some instance variables given the value at init time.

In Java I don’t know how to do that. Currently I do the following:

public class SpecialScreen extends BASEScreen{
private static final int ACTIVITY_1 = 1;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState); //create the instance
    defineScreenType (ACTIVITY_1); //second call to set the instance variable
    presentOnScreen();
}

While in BASEScreen:

public class BASEScreen extends Activity {
private Integer activityCode; // which activity should I do?

@Override
public void onCreate(Bundle savedInstanceState) {  // the creation
    super.onCreate(savedInstanceState);
}

// the setting of the instance variable
public void defineScreenType(int screenID) {
    activityCode = screenID;

}

This can’t be the best way of doing it. How to do this better?

Thanks

ADDED to show the calling of the SpecialScreen within BASEScreen:

    @Override
public boolean onMenuItemSelected(int featureId, MenuItem item) {
    Intent i;
    switch (item.getItemId()) {
    case OTHER_PAGE_ID:
        // 
        if (activityCode == ACTIVITY_1) {
            i = new Intent(this, SpecialScreen2.class);
            i.putExtra("Task", ACTIVITY_2);
            startActivityForResult(i, ACTIVITY_2);
            finish();

        } else {
            i = new Intent(this, SpecialScreen1.class);
            i.putExtra("Task", ACTIVITY_1);
            startActivityForResult(i, ACTIVITY_1);
            finish();
        }

        return true;

ps I know that putting the Extra is not required anymore. This was the way I did it before I had the two SpecialScreen subclasses and always called the BASEScreen with this parameter.

Answer 1

Correct, there is no “default” syntax like in c++. You have to do it in the constructor. Mind you, you don’t need to use the setter method, you could make activityCode protected rather than private, and just do:

activityCode = ACTIVITY_1;

The other option is using the Builder Pattern to construct your objects, using a set of defaults inside the builder that you override (when needed) when requesting the object be built.

Edit in response to comments below:

I apologize for some confusion as I was calling it a “constructor” when it’s not.

If in BASEScreen you change the access to protected from private

public class BASEScreen extends Activity {
    protected Integer activityCode;

You can then access that in the SpecialScreen subclass:

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    activityCode = 1; // Or ACTIVITY_1 if you'd like
    presentOnScreen();
}