date picker in android type one

MAIN ACTIVITY  JAVA
package com.example.viraj.datepicker;


import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

import android.widget.TextView;
import android.widget.DatePicker;
import android.widget.Toast;

import static android.widget.Toast.makeText;


public class MainActivity extends AppCompatActivity {



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        final DatePicker datePicker = (DatePicker) findViewById(R.id.Datepick);
        final Button button = (Button) findViewById(R.id.set);

        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Toast.makeText(MainActivity.this, datePicker.getDayOfMonth()+""+datePicker.getMonth()+""+datePicker.getYear(),Toast.LENGTH_LONG).show();
            }
        });
    }


}

XML FILE

<?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"

    android:layout_margin="10dp"

    tools:context="com.example.viraj.datepicker.MainActivity">

    <TextView

        android:id="@+id/text"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:text="Select date and press set button" />

    <DatePicker

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:id="@+id/Datepick"

        android:layout_below="@+id/set"

        app:layout_constraintTop_toTopOf="parent"

        tools:layout_editor_absoluteX="8dp"

        android:layout_marginTop="-29dp" />

    <Button

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:id="@+id/set"

        android:text="Set"

        android:layout_below="@id/text"

        android:layout_marginLeft="8dp"

        app:layout_constraintLeft_toLeftOf="parent"

        android:layout_marginRight="8dp"

        app:layout_constraintRight_toRightOf="parent"

        app:layout_constraintBottom_toBottomOf="parent"

        android:layout_marginBottom="8dp" />

</android.support.constraint.ConstraintLayout>