To open Calendar on Clicking the EditText follow the steps mentioned below:-

1) Create a Edit Text in your xml file.

activity_main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
     tools:context=".MainActivity"
    android:orientation="vertical">

<EditText
            android:singleLine="true"
            android:id="@+id/dob_et"
            android:layout_marginTop="20dp"
            android:layout_marginRight="20dp"
            android:focusable="false"
            android:hint="Date of birth"
            android:inputType="date"
            android:layout_width="match_parent"
            android:layout_height="wrap_content" />

</LinearLayout>

2) Now initialize  Edit Text in your java file. Here I have used the method DateDialog() to open the calendar popup and select the date.

MainActivity.java

public class MainActivity extends AppCompatActivity { 

     private Calendar mcalendar;     
     private EditText mdob_et;
     private int day,month,year;

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

        mdob_et=(EditText)findViewById(R.id.dob_et);
        mdob_et.setOnClickListener(mClickListener);
        day=mcalendar.get(Calendar.DAY_OF_MONTH);
        year=mcalendar.get(Calendar.YEAR);
        month=mcalendar.get(Calendar.MONTH);

}

View.OnClickListener mClickListener=new View.OnClickListener() {
    @Override
    public void onClick(View v) {

    DateDialog();

    }
};

 public void DateDialog(){

        DatePickerDialog.OnDateSetListener listener=new DatePickerDialog.OnDateSetListener() {

            @Override
            public void onDateSet(DatePicker view, int year, int monthOfYear,int dayOfMonth)
            {

                mdob_et.setText(dayOfMonth + "/" + monthOfYear + "/" + year);

            }};

     DatePickerDialog dpDialog=new DatePickerDialog(getActivity(), listener, year, month, day);
        dpDialog.show();

    }
}