XML Stack Overflow

I'm new to android development, this is just my second app i built just to kill time, though, i could'nt understand, what caused this error. Need expert advice

The activity_starting_point.xml:

<LinearLayout xmlns:android="http://ift.tt/nIICcg"
    xmlns:tools="http://ift.tt/LrGmb4"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".StatingPoint" >

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="35dp"
        android:text="Enter Number 1"
          android:id="@+id/tvDisplay"
           />

    <EditText
        android:id="@+id/editText1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10"
        android:inputType="number" >

        <requestFocus />
    </EditText>

    <TextView

        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="35dp"
        android:text="Enter Number 2" 
          android:id="@+id/tvDisplay"
        />

    <EditText
        android:id="@+id/editText2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10"
        android:inputType="number" />

    <Button
        android:id="@+id/button1"
        android:layout_width="250dp"
        android:layout_height="wrap_content"
        android:text="Add"
        android:layout_gravity="center" />

    <Button
        android:id="@+id/button1"
        android:layout_width="250dp"
        android:layout_height="wrap_content"
        android:text="Subtract"
        android:layout_gravity="center" />

       <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text=" Your Total is 0 "  
        android:textSize="45dp"
        android:layout_gravity="center"
        android:gravity="center"
        android:id="@+id/tvDisplay" />

</LinearLayout>

The Java class file: StartingPoint.java package com.ankur.calulator;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;


public class StatingPoint extends Activity {


    int num1,num2;
    int total;
    Button add,sub;
    TextView display;
    EditText no1,no2;



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

        total=0;
        no1=(EditText) findViewById(R.id.editText1);
        no2=(EditText) findViewById(R.id.editText2);
        display=(TextView)findViewById(R.id.tvDisplay);

        add.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View arg0) {
                // TODO Auto-generated method stub

                total=num1+num2;
                display.setText("Your Total is "+total);

            }
        });

        sub.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View arg0) {
                // TODO Auto-generated method stub

                total=num1-num2;
                display.setText("Your Total is "+total);

            }
        });
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.activity_stating_point, menu);
        return true;
    }

}

The logcat file: its got blank, i think i messed up with it, though i saw something as java null pointer exception before i knw i'm close, just nt able to find some missing link, need advice.