how to use camera in android studio| code

activity_main.xml(layout)

<?xml version="1.0" encoding="utf-8"?>

<RelativeLayout 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"

    android:paddingBottom="@dimen/activity_vertical_margin"

    android:paddingLeft="@dimen/activity_horizontal_margin"

    android:paddingRight="@dimen/activity_horizontal_margin" 

   android:paddingTop="@dimen/activity_vertical_margin"  

  tools:context="com.example.avi.trial.MainActivity">

    <Button 

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    android:id="@+id/btn1"

    android:background="@mipmap/camera"/>


</RelativeLayout>

*******************************************************************************************

MainActivity.java

package com.example.avi.trial;

import android.content.DialogInterface;
import android.content.Intent;
import android.provider.MediaStore;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;

public class MainActivity extends AppCompatActivity {
ImageView imgvw1;
    Button btn1;
    @Override    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        init();
        btn1.setOnClickListener(new View.OnClickListener() {
            @Override            public void onClick(View v)
            {
                Intent intent=new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
                startActivityForResult(intent,100);
            }
        });
    }

    private void init()
    {

        btn1= (Button) findViewById(R.id.btn1);
    }
}