Add two number by using Edit text , Text view and Button

Activity main xml Code:

<?xml version="1.0" encoding="utf-8"?><android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"    

xmlns:app="http://schemas.android.com/apk/res-auto"

    xmlns:tools="http://schemas.android.com/tools"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    tools:context="com.example.seam.addtonumber.MainActivity">

    <Button

        android:id="@+id/button"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:text="Button"

        android:layout_marginTop="161dp"

        app:layout_constraintTop_toBottomOf="@+id/editText"

        android:layout_marginRight="8dp"

        app:layout_constraintRight_toRightOf="parent"

        android:layout_marginLeft="8dp"

        app:layout_constraintLeft_toLeftOf="parent"

        app:layout_constraintBottom_toBottomOf="parent"

        android:layout_marginBottom="8dp" />

    <EditText

        android:id="@+id/editText"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_marginTop="90dp"

        android:ems="10"

        android:inputType="textPersonName"

        app:layout_constraintHorizontal_bias="0.39"

        app:layout_constraintLeft_toLeftOf="parent"

        app:layout_constraintRight_toRightOf="parent"

        app:layout_constraintTop_toTopOf="parent" />

    <TextView

        android:id="@+id/textView"

        android:layout_width="203dp"

        android:layout_height="30dp"

        android:layout_marginBottom="25dp"

        app:layout_constraintBottom_toTopOf="@+id/button"

        app:layout_constraintHorizontal_bias="0.502"

 app:layout_constraintLeft_toLeftOf="parent"

        app:layout_constraintRight_toRightOf="parent"

        android:layout_marginTop="8dp"

        app:layout_constraintTop_toBottomOf="@+id/editText2"

        app:layout_constraintVertical_bias="0.87" />

    <EditText

        android:id="@+id/editText2"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_marginBottom="8dp"

        android:layout_marginTop="8dp"

        android:ems="10"

        android:inputType="textPersonName"

        app:layout_constraintBottom_toBottomOf="parent"

        app:layout_constraintLeft_toLeftOf="parent"

        app:layout_constraintRight_toRightOf="parent"

        app:layout_constraintTop_toBottomOf="@+id/editText"

        app:layout_constraintVertical_bias="0.159"

        app:layout_constraintHorizontal_bias="0.39" />

</android.support.constraint.ConstraintLayout>

Main Activity java code:

package com.example.seam.addtonumber;

import android.provider.Settings;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {


    private EditText edittext1,edittext2;
    TextView tv;
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        setOnbutton();
    }
    public void setOnbutton()
    {
        Button bt=(Button) findViewById(R.id.button);
        //EditText e=(EditText)findViewById(R.id.editText);        edittext1=(EditText)findViewById(R.id.editText);
        edittext2=(EditText)findViewById(R.id.editText2);
        tv=(TextView)findViewById(R.id.textView);
        bt.setOnClickListener(new View.OnClickListener()
        {
            public void onClick(View v)
            {
                String value1=edittext1.getText().toString();
                String v2=edittext2.getText().toString();
                int a=Integer.parseInt(value1);
                int b=Integer.parseInt(v2);
                tv.setText(String.valueOf(a+ b));

            }
        });
    }
}