getting error in Android Studio(IDE).....Unfortunately,The new Boston has stopped...why this error come?

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XML

Java

Mobile

Android

MYcode is....
.JAVA File

package com.thenewboston.travis;

import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.os.Build;
import android.widget.Button;
import android.widget.TextView;

public class startingPoint extends ActionBarActivity {
int counter;
Button add;
Button sub;
TextView display;



@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_starting_point);
counter=0;
add=(Button) findViewById(R.id.bAdd);
sub=(Button) findViewById(R.id.bSub);
display=(TextView) findViewById(R.id.tvDisplay);

add.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
counter++;
display.setText("Your Total is 0");
}
});
sub.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
counter--;
display.setText("Your Total is 0");
}
});

}


@Override
public boolean onCreateOptionsMenu(Menu menu) {

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

/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends Fragment {

public PlaceholderFragment() {
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_starting_point, container, false);
return rootView;
}
}

}

############################################################################

.XML File


<linearlayout xmlns:android="http://schemas.android.com/apk/res/android"> xmlns:tools="http://schemas.android.com/tools"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >

<textview>
android:id="@+id/tvDisplay"
android:text="Your total is 0"
android:layout_width="fill_parent"
android:layout_height="wrap_content"

android:gravity="center"
android:textSize="45dp"/>
<relativelayout>
android:layout_width="match_parent"
android:layout_height="match_parent">
<Button

android:layout_width="302dp"
android:layout_height="50dp"

android:layout_gravity="center_vertical"
android:text="ADD ONE"

android:id="@+id/bAdd"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true" />

<Button
android:layout_width="302dp"
android:layout_height="50dp"

android:layout_gravity="center_vertical"
android:text="SUBTRACT ONE"

android:layout_below="@+id/bSub"
android:layout_centerHorizontal="true" />