Button gedrückt lassen

public class MainActivity extends ActionBarActivity implements View.OnClickListener {

    ProgressBar bar;
    Button btn;
    int i = 1;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        bar = (ProgressBar)findViewById(R.id.progressBar);
        bar.setMax(100);
        btn = (Button)findViewById(R.id.button);
        btn.setOnClickListener(this);
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {

        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    public void onClick(View v){
        if(v == btn){
            i += 4;

            if(i >= 100){
                AlertDialog ad = new AlertDialog.Builder(this).create();
                ad.setMessage("Fertig");
                ad.show();

                i = 0;
            }

            bar.setProgress(i);

        }
    }

}