bar graph using AChartEngine library

I have a bar graph using AChartEngine library as shown below ::

public class MainActivity extends Activity {

  private String[] mMonth = new String[] {
            "Jan", "Feb" , "Mar", "Apr", "May", "Jun",
            "Jul", "Aug" , "Sep", "Oct", "Nov", "Dec"
        };

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

    // Getting reference to the button btn_chart
    Button btnChart = (Button) findViewById(R.id.btn_chart);

    // Defining click event listener for the button btn_chart
    OnClickListener clickListener = new OnClickListener() {

        @Override
        public void onClick(View v) {
            // Draw the Income vs Expense Chart
            openChart();                
        }
    };

    // Setting event click listener for the button btn_chart of the MainActivity layout
    btnChart.setOnClickListener(clickListener);

}

private void openChart(){
    int[] x = { 0,1,2,3,4,5,6,7 };
    int[] income = { 2000,2500,2700,3000,2800,3500,3700,3800};
    int[] expense = {2200, 2700, 2900, 2800, 2600, 3000, 3300, 3400 };

    // Creating an  XYSeries for Income
    //CategorySeries incomeSeries = new CategorySeries("Income");
    XYSeries incomeSeries = new XYSeries("Income");
    // Creating an  XYSeries for Income
    XYSeries expenseSeries = new XYSeries("Expense");
    // Adding data to Income and Expense Series
    for(int i=0;i<x.length;i++){            
        incomeSeries.add(i,income[i]);
        expenseSeries.add(i,expense[i]);
    }


    // Creating a dataset to hold each series
    XYMultipleSeriesDataset dataset = new XYMultipleSeriesDataset();
    // Adding Income Series to the dataset
    dataset.addSeries(incomeSeries);
    // Adding Expense Series to dataset
    dataset.addSeries(expenseSeries);       

    // Creating XYSeriesRenderer to customize incomeSeries
    XYSeriesRenderer incomeRenderer