java.lang.runtimeexception java.lang.nullpointerexception

gistfile1.txt

my code is 

i am getting error at the end of this line of code "quantityTextView.setText("" + number);" 

Error is : java.lang.runtimeexception java.lang.nullpointerexception 

Using platform : android studio TextView.setText("" + number)


// FIND FULL CODE 


package com.example.android.justjava;

import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.view.View;
import android.widget.TextView;

/**
 * This app displays an order form to order coffee.
 */
public class MainActivity extends ActionBarActivity {

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

    /**
     * This method is called when the order button is clicked.
     */
    public void submitOrder(View view) {
        display(1);
    }

    /**
     * This method displays the given quantity value on the screen.
     */
    private void display(int number) {
        TextView quantityTextView = (TextView) findViewById(R.id.quantity_text_view);
        quantityTextView.setText("" + number);
    }
}

Make sure id quantity_text_view exist in your xml layout file.