Simply call camera

public void startCamera(View view){
    Intent intent=new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
    startActivity(intent);
}

//布局

<?xml version="1.0" encoding="utf-8"?>
<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"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="startCameras"
        android:text="camera"/>
</LinearLayout>