这段代码是为一个按钮编写的，这个按钮应该在android模拟器上。但是，当我把这段代码放在main activity.kt中时，它给了我多个错误。我遇到的第一个错误是main activity第9行的重新声明错误

package com.example.android.justjava

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

// This activity displays an order form to order coffee.
class MainActivity : ActionBarActivity() {
    protected fun onCreate(savedInstanceState: Bundle) {
      super.onCreate(savedInstanceState)
      setContentView(R.layout.activity_main)
    }

    // this method is called when the order button is clicked.
    fun submitOrder(view: View) {
      display(1)
    }

    // This method displays the given quantity value on the screen.
    private fun display(number: Int) {
      val quantityTextView = findViewById(R.id.quantity_text_view as TextView
      quantityTextView.text = "" + number
    }
}

此活动显示订购咖啡的订单。

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);
   }
}