Removing Objects from an ArrayList

Question

Hi I am a bit new to Java and Android. I am working on a project which it cycles through random Activities and I am stuck with a problem for days.

public class ActivityHelper extends Activity {
    ArrayList<String> classes = new ArrayList<String>();
    public   void addClass (){
        classes.add("Activity1");
        classes.add("Activity2");
        classes.add("Activity3");
                //etc

    }
    public  String openClass (){
        addClass();
        Random rand = new Random ();
        int crazy = rand.nextInt(classes.size());
        String cheese = classes.get(crazy);
        classes.remove(cheese);
        return cheese;  
    }   
}

// A Method in Activity1 extends ActivityHelper
public void doJob() {

    String cheese = openClass();
    try {               
        @SuppressWarnings("rawtypes")
        Class ourClass = Class.forName("com.activity.dan." + cheese);
        Intent ourIntent = new Intent(Activity1.this, ourClass);
        startActivity(ourIntent);
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    }
}

The program perfectly cycles through the classes but my problem is the classes.remove(cheese); doesnt work. I am hoping once the Class is opened it will be removed from the ArrayList and wont be used again if the doJob(); method is called on another class. I tried using static and putting the remove list in the Activity1 but nothing seems to work. Your help will be appreciated.

where do you call all these methods? what is your onCreate()? — Sergey Benner
– Sergey Benner, Commented Mar 12, 2012 at 13:22
use this classes.remove(crazy) instead of classes.remove(cheese) because remove method take an index of item see sun java docs — ρяσѕρєя K
– ρяσѕρєя K, Commented Mar 12, 2012 at 13:25

zapl · Accepted Answer · 2012-03-13 09:59:51Z

1

I guess your remove is working but each Activity you create contains a new instance of classes and that's not what you want. It might work this way.

public class ActivityHelper extends Activity{
static ArrayList<String> classes = new ArrayList<String>();
static {
    classes.add("Activity1");
    classes.add("Activity2");
    classes.add("Activity3");
            //etc
}
public  String openClass (){
    // don't add classes here - would be done every time.
    // print out some debug
    Log.d("ActivityHelper", "State before openClass: " + Arrays.toString(classes.toArray()));
    Random rand = new Random ();
    int crazy = rand.nextInt(classes.size());
    String cheese = classes.get(crazy);
    classes.remove(crazy);
    // print out some debug
    Log.d("ActivityHelper", "State after openClass: " + Arrays.toString(classes.toArray()));
    return cheese;
}

edited Mar 13, 2012 at 9:59

answered Mar 12, 2012 at 13:27

zapl

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3 Comments

dan pasco Over a year ago

Hi tried this method but still it seems to be creating a new Instance of the class. Also tried removing via index but still same case. I am hoping to work around it and try a ArrayList of Classes and randomly cycle through them if possible. Any thoughts?

zapl Over a year ago

if you print (e.g. Log.d("TAG", Arrays.toString(classes.toArray()));) the content of classes in openClass is the content really reset all the time? Because if classes is static then it will exist only once for all instances of your Activity. That will not work if your Activities are in different apps or processes though. And a restart of your app (kill with some TaskManager) might reset classes as well.

zapl Over a year ago

@danpasco I've added some debug to the Answer. It should print a list that always gets smaller. If not you might need to use e.g. SharedPreferences to keep a list of Activities you still want to be opened.

Job Brown · Accepted Answer · 2012-03-12 13:18:02Z

0

ArrayList.remove() expects an Integer, not a class. Call .remove() with the Integer index you want to remove and it should work as expected.

answered Mar 12, 2012 at 13:18

Job Brown

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3 Comments

Adam Over a year ago

remove() is overloaded. remove(int) and remove(Object)

ρяσѕρєя K Over a year ago

@SergeyBenner: hi,can you give me an example where we pass an object in ArrayList.remove(int index) apart from Integer Object.

Job Brown Over a year ago

By bad, didn't see that it accepted Object as a parameter. Either wa try removing by index? Clearly not working for Object

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