if(activityrunning == activity1)
//do this
else if (activityrunning == activity2)
//do something else

class MyActivity extends Activity {
     static boolean active = false;

      @Override
      public void onStart() {
         super.onStart();
         active = true;
      }

      @Override
      public void onStop() {
         super.onStop();
         active = false;
      }
}

public boolean isRunning(Context ctx) {
        ActivityManager activityManager = (ActivityManager) ctx.getSystemService(Context.ACTIVITY_SERVICE);
        List<RunningTaskInfo> tasks = activityManager.getRunningTasks(Integer.MAX_VALUE);

        for (RunningTaskInfo task : tasks) {
            if (ctx.getPackageName().equalsIgnoreCase(task.baseActivity.getPackageName()))
                return true;
        }

        return false;
    }

public class example extends Activity {

    @Override
    protected void onStart() {
        super.onStart();

        // Store our shared preference
        SharedPreferences sp = getSharedPreferences("OURINFO", MODE_PRIVATE);
        Editor ed = sp.edit();
        ed.putBoolean("active", true);
        ed.commit();
    }

    @Override
    protected void onStop() {
        super.onStop();

        // Store our shared preference
        SharedPreferences sp = getSharedPreferences("OURINFO", MODE_PRIVATE);
        Editor ed = sp.edit();
        ed.putBoolean("active", false);
        ed.commit();

    }
}

public static boolean isServiceRunning(Context context) {

    Log.i(TAG, "Checking if service is running");

    ActivityManager activityManager = (ActivityManager)context.getSystemService(Context.ACTIVITY_SERVICE);

    List<RunningServiceInfo> services = activityManager.getRunningServices(Integer.MAX_VALUE);

    boolean isServiceFound = false;

    for (int i = 0; i < services.size(); i++) {

        if (Constants.PACKAGE.equals(services.get(i).service.getPackageName())){

            if (Constants.BACKGROUND_SERVICE_CLASS.equals(services.get(i).service.getClassName())){
                isServiceFound = true;
            }
        }
    }

    Log.i(TAG, "Service was" + (isServiceFound ? "" : " not") + " running");

    return isServiceFound;

}

protected Boolean isActivityRunning(Class activityClass)
{
        ActivityManager activityManager = (ActivityManager) getBaseContext().getSystemService(Context.ACTIVITY_SERVICE);
        List<ActivityManager.RunningTaskInfo> tasks = activityManager.getRunningTasks(Integer.MAX_VALUE);

        for (ActivityManager.RunningTaskInfo task : tasks) {
            if (activityClass.getCanonicalName().equalsIgnoreCase(task.baseActivity.getClassName()))
                return true;
        }

        return false;
}

Activity#getWindow().getDecorView().getRootView().isShown()

public boolean isServiceRunning() {

ActivityManager activityManager = (ActivityManager)Monitor.this.getSystemService (Context.ACTIVITY_SERVICE);
    List<RunningTaskInfo> services = activityManager.getRunningTasks(Integer.MAX_VALUE);
    isServiceFound = false;
    for (int i = 0; i < services.size(); i++) {
        if (services.get(i).topActivity.toString().equalsIgnoreCase("ComponentInfo{com.lyo.AutoMessage/com.lyo.AutoMessage.TextLogList}")) {
            isServiceFound = true;
        }
    }
    return isServiceFound;
}

<uses-permission  android:name="android.permission.GET_TASKS"/>

@protected
void doSomething() {
}

private static boolean mainActivityIsOpen;

public static boolean mainActivityIsOpen() {
    return mainActivityIsOpen;
}

public static void mainActivityIsOpen(boolean mainActivityIsOpen) {
    DayView.mainActivityIsOpen = mainActivityIsOpen;
}

if (MainActivity.mainActivityIsOpen() == false)
{
                //do something
}
else if(MainActivity.mainActivityIsOpen() == true)
{//or just else. . . ( or else if, does't matter)
        //do something
}

@Override
protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            if ((getIntent().getFlags() & Intent.FLAG_ACTIVITY_BROUGHT_TO_FRONT) != 0) {
                // Activity is being brought to front and not being  created again,
                // Thus finishing this activity will bring the last viewed activity to foreground
                finish();
            }
    }

class MyActivity extends Activity {

     static int activeInstances = 0;

     static boolean isActive() {
        return (activeInstance > 0)
     }

      @Override
      public void onStart() {
         super.onStart();
         activeInstances++;
      }

      @Override
      public void onStop() {
         super.onStop();
         activeInstances--;
      }
}