diff --git a/app/build.gradle b/app/build.gradle
index 867c048..87017a7 100644
--- a/app/build.gradle
+++ b/app/build.gradle
@@ -3,7 +3,7 @@ apply plugin: 'android-apt'
 
 android {
     compileSdkVersion 23
-    buildToolsVersion "23.0.2"
+    buildToolsVersion "23.0.3"
 
     defaultConfig {
         applicationId "com.simplemobiletools.draw"
diff --git a/app/src/main/AndroidManifest.xml b/app/src/main/AndroidManifest.xml
index bc802aa..1135034 100644
--- a/app/src/main/AndroidManifest.xml
+++ b/app/src/main/AndroidManifest.xml
@@ -12,7 +12,7 @@
         android:supportsRtl="true"
         android:theme="@style/AppTheme">
         <activity
-            android:name=".MainActivity"
+            android:name=".activities.MainActivity"
             android:screenOrientation="portrait">
             <intent-filter>
                 <action android:name="android.intent.action.MAIN"/>
@@ -22,12 +22,12 @@
         </activity>
 
         <activity
-            android:name=".AboutActivity"
+            android:name=".activities.AboutActivity"
             android:label="@string/about"
             android:screenOrientation="portrait"/>
 
         <activity
-            android:name=".LicenseActivity"
+            android:name=".activities.LicenseActivity"
             android:label="@string/third_party_licences"
             android:screenOrientation="portrait"/>
 
diff --git a/app/src/main/java/com/simplemobiletools/draw/MyCanvas.java b/app/src/main/java/com/simplemobiletools/draw/MyCanvas.java
index a5b6bde..a53c11e 100644
--- a/app/src/main/java/com/simplemobiletools/draw/MyCanvas.java
+++ b/app/src/main/java/com/simplemobiletools/draw/MyCanvas.java
@@ -14,53 +14,54 @@ import java.util.LinkedHashMap;
 import java.util.Map;
 
 public class MyCanvas extends View {
-    private Paint paint;
-    private Path path;
-    private Map<Path, Integer> paths;
-    private int color;
-    private float curX;
-    private float curY;
-    private float startX;
-    private float startY;
-    private PathsChangedListener listener;
+    private Paint mPaint;
+    private Path mPath;
+    private Map<Path, Integer> mPaths;
+    private PathsChangedListener mListener;
+
+    private int mColor;
+    private float mCurX;
+    private float mCurY;
+    private float mStartX;
+    private float mStartY;
 
     public MyCanvas(Context context, AttributeSet attrs) {
         super(context, attrs);
 
-        path = new Path();
-        paint = new Paint();
-        paint.setColor(Color.BLACK);
-        paint.setStyle(Paint.Style.STROKE);
-        paint.setStrokeJoin(Paint.Join.ROUND);
-        paint.setStrokeCap(Paint.Cap.ROUND);
-        paint.setStrokeWidth(5f);
-        paint.setAntiAlias(true);
+        mPath = new Path();
+        mPaint = new Paint();
+        mPaint.setColor(Color.BLACK);
+        mPaint.setStyle(Paint.Style.STROKE);
+        mPaint.setStrokeJoin(Paint.Join.ROUND);
+        mPaint.setStrokeCap(Paint.Cap.ROUND);
+        mPaint.setStrokeWidth(5f);
+        mPaint.setAntiAlias(true);
 
-        paths = new LinkedHashMap<>();
-        paths.put(path, paint.getColor());
+        mPaths = new LinkedHashMap<>();
+        mPaths.put(mPath, mPaint.getColor());
         pathsUpdated();
     }
 
     public void setListener(PathsChangedListener listener) {
-        this.listener = listener;
+        this.mListener = listener;
     }
 
     public void undo() {
-        if (paths.size() <= 0)
+        if (mPaths.size() <= 0)
             return;
 
         Path lastKey = null;
-        for (Path key : paths.keySet()) {
+        for (Path key : mPaths.keySet()) {
             lastKey = key;
         }
 
-        paths.remove(lastKey);
+        mPaths.remove(lastKey);
         pathsUpdated();
         invalidate();
     }
 
     public void setColor(int newColor) {
-        color = newColor;
+        mColor = newColor;
     }
 
     public Bitmap getBitmap() {
@@ -75,46 +76,46 @@ public class MyCanvas extends View {
     protected void onDraw(Canvas canvas) {
         super.onDraw(canvas);
 
-        for (Map.Entry<Path, Integer> entry : paths.entrySet()) {
-            paint.setColor(entry.getValue());
-            canvas.drawPath(entry.getKey(), paint);
+        for (Map.Entry<Path, Integer> entry : mPaths.entrySet()) {
+            mPaint.setColor(entry.getValue());
+            canvas.drawPath(entry.getKey(), mPaint);
         }
 
-        paint.setColor(color);
-        canvas.drawPath(path, paint);
+        mPaint.setColor(mColor);
+        canvas.drawPath(mPath, mPaint);
     }
 
     private void actionDown(float x, float y) {
-        path.reset();
-        path.moveTo(x, y);
-        curX = x;
-        curY = y;
+        mPath.reset();
+        mPath.moveTo(x, y);
+        mCurX = x;
+        mCurY = y;
     }
 
     private void actionMove(float x, float y) {
-        path.quadTo(curX, curY, (x + curX) / 2, (y + curY) / 2);
-        curX = x;
-        curY = y;
+        mPath.quadTo(mCurX, mCurY, (x + mCurX) / 2, (y + mCurY) / 2);
+        mCurX = x;
+        mCurY = y;
     }
 
     private void actionUp() {
-        path.lineTo(curX, curY);
+        mPath.lineTo(mCurX, mCurY);
 
         // draw a dot on click
-        if (startX == curX && startY == curY) {
-            path.lineTo(curX, curY + 2);
-            path.lineTo(curX + 1, curY + 2);
-            path.lineTo(curX + 1, curY);
+        if (mStartX == mCurX && mStartY == mCurY) {
+            mPath.lineTo(mCurX, mCurY + 2);
+            mPath.lineTo(mCurX + 1, mCurY + 2);
+            mPath.lineTo(mCurX + 1, mCurY);
         }
 
-        paths.put(path, paint.getColor());
+        mPaths.put(mPath, mPaint.getColor());
         pathsUpdated();
-        path = new Path();
+        mPath = new Path();
     }
 
     private void pathsUpdated() {
-        if (listener != null && paths != null) {
-            listener.pathsChanged(paths.size());
+        if (mListener != null && mPaths != null) {
+            mListener.pathsChanged(mPaths.size());
         }
     }
 
@@ -125,8 +126,8 @@ public class MyCanvas extends View {
 
         switch (event.getAction()) {
             case MotionEvent.ACTION_DOWN:
-                startX = x;
-                startY = y;
+                mStartX = x;
+                mStartY = y;
                 actionDown(x, y);
                 break;
             case MotionEvent.ACTION_MOVE:
diff --git a/app/src/main/java/com/simplemobiletools/draw/AboutActivity.java b/app/src/main/java/com/simplemobiletools/draw/activities/AboutActivity.java
similarity index 59%
rename from app/src/main/java/com/simplemobiletools/draw/AboutActivity.java
rename to app/src/main/java/com/simplemobiletools/draw/activities/AboutActivity.java
index 1be6943..c0caa7d 100644
--- a/app/src/main/java/com/simplemobiletools/draw/AboutActivity.java
+++ b/app/src/main/java/com/simplemobiletools/draw/activities/AboutActivity.java
@@ -1,4 +1,4 @@
-package com.simplemobiletools.draw;
+package com.simplemobiletools.draw.activities;
 
 import android.content.Intent;
 import android.content.res.Resources;
@@ -8,6 +8,9 @@ import android.text.Html;
 import android.text.method.LinkMovementMethod;
 import android.widget.TextView;
 
+import com.simplemobiletools.draw.BuildConfig;
+import com.simplemobiletools.draw.R;
+
 import java.util.Calendar;
 
 import butterknife.BindView;
@@ -15,17 +18,18 @@ import butterknife.ButterKnife;
 import butterknife.OnClick;
 
 public class AboutActivity extends AppCompatActivity {
-    @BindView(R.id.about_copyright) TextView copyright;
-    @BindView(R.id.about_version) TextView version;
-    @BindView(R.id.about_email) TextView emailTV;
-    private Resources res;
+    @BindView(R.id.about_copyright) TextView mCopyright;
+    @BindView(R.id.about_version) TextView mVersion;
+    @BindView(R.id.about_email) TextView mEmailTV;
+
+    private Resources mRes;
 
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_about);
         ButterKnife.bind(this);
-        res = getResources();
+        mRes = getResources();
 
         setupEmail();
         setupVersion();
@@ -33,23 +37,23 @@ public class AboutActivity extends AppCompatActivity {
     }
 
     private void setupEmail() {
-        final String email = res.getString(R.string.email);
-        final String appName = res.getString(R.string.app_name);
+        final String email = mRes.getString(R.string.email);
+        final String appName = mRes.getString(R.string.app_name);
         final String href = "<a href=\"mailto:" + email + "?subject=" + appName + "\">" + email + "</a>";
-        emailTV.setText(Html.fromHtml(href));
-        emailTV.setMovementMethod(LinkMovementMethod.getInstance());
+        mEmailTV.setText(Html.fromHtml(href));
+        mEmailTV.setMovementMethod(LinkMovementMethod.getInstance());
     }
 
     private void setupVersion() {
         final String versionName = BuildConfig.VERSION_NAME;
-        final String versionText = String.format(res.getString(R.string.version), versionName);
-        version.setText(versionText);
+        final String versionText = String.format(mRes.getString(R.string.version), versionName);
+        mVersion.setText(versionText);
     }
 
     private void setupCopyright() {
         final int year = Calendar.getInstance().get(Calendar.YEAR);
-        final String copyrightText = String.format(res.getString(R.string.copyright), year);
-        copyright.setText(copyrightText);
+        final String copyrightText = String.format(mRes.getString(R.string.copyright), year);
+        mCopyright.setText(copyrightText);
     }
 
     @OnClick(R.id.about_license)
diff --git a/app/src/main/java/com/simplemobiletools/draw/LicenseActivity.java b/app/src/main/java/com/simplemobiletools/draw/activities/LicenseActivity.java
similarity index 91%
rename from app/src/main/java/com/simplemobiletools/draw/LicenseActivity.java
rename to app/src/main/java/com/simplemobiletools/draw/activities/LicenseActivity.java
index 9f1f131..74ad647 100644
--- a/app/src/main/java/com/simplemobiletools/draw/LicenseActivity.java
+++ b/app/src/main/java/com/simplemobiletools/draw/activities/LicenseActivity.java
@@ -1,14 +1,17 @@
-package com.simplemobiletools.draw;
+package com.simplemobiletools.draw.activities;
 
 import android.content.Intent;
 import android.net.Uri;
 import android.os.Bundle;
 import android.support.v7.app.AppCompatActivity;
 
+import com.simplemobiletools.draw.R;
+
 import butterknife.ButterKnife;
 import butterknife.OnClick;
 
 public class LicenseActivity extends AppCompatActivity {
+
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
diff --git a/app/src/main/java/com/simplemobiletools/draw/MainActivity.java b/app/src/main/java/com/simplemobiletools/draw/activities/MainActivity.java
similarity index 92%
rename from app/src/main/java/com/simplemobiletools/draw/MainActivity.java
rename to app/src/main/java/com/simplemobiletools/draw/activities/MainActivity.java
index 5b64dad..55a0d1f 100644
--- a/app/src/main/java/com/simplemobiletools/draw/MainActivity.java
+++ b/app/src/main/java/com/simplemobiletools/draw/activities/MainActivity.java
@@ -1,4 +1,4 @@
-package com.simplemobiletools.draw;
+package com.simplemobiletools.draw.activities;
 
 import android.Manifest;
 import android.content.Intent;
@@ -21,6 +21,10 @@ import android.view.View;
 import android.widget.EditText;
 import android.widget.Toast;
 
+import com.simplemobiletools.draw.MyCanvas;
+import com.simplemobiletools.draw.R;
+import com.simplemobiletools.draw.Utils;
+
 import java.io.ByteArrayOutputStream;
 import java.io.File;
 import java.io.FileOutputStream;
@@ -38,19 +42,20 @@ public class MainActivity extends AppCompatActivity implements MyCanvas.PathsCha
     private static final String SAVE_FOLDER_NAME = "Simple Draw";
     private static final int STORAGE_PERMISSION = 1;
 
-    @BindView(R.id.my_canvas) MyCanvas myCanvas;
-    @BindView(R.id.undo) View undoBtn;
-    @BindView(R.id.color_picker) View colorPicker;
+    @BindView(R.id.my_canvas) MyCanvas mMyCanvas;
+    @BindView(R.id.undo) View mUndoBtn;
+    @BindView(R.id.color_picker) View mColorPicker;
+
+    private String curFileName;
 
     private int color;
-    private String curFileName;
 
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);
         ButterKnife.bind(this);
-        myCanvas.setListener(this);
+        mMyCanvas.setListener(this);
 
         setColor(Color.BLACK);
     }
@@ -141,7 +146,7 @@ public class MainActivity extends AppCompatActivity implements MyCanvas.PathsCha
             }
         }
 
-        final Bitmap bitmap = myCanvas.getBitmap();
+        final Bitmap bitmap = mMyCanvas.getBitmap();
         FileOutputStream out = null;
         try {
             final File file = new File(directory, fileName);
@@ -166,7 +171,7 @@ public class MainActivity extends AppCompatActivity implements MyCanvas.PathsCha
 
     private void shareImage() {
         final String shareTitle = getResources().getString(R.string.share_via);
-        final Bitmap bitmap = myCanvas.getBitmap();
+        final Bitmap bitmap = mMyCanvas.getBitmap();
         final Intent sendIntent = new Intent();
         final Uri uri = getImageUri(bitmap);
         if (uri == null)
@@ -211,7 +216,7 @@ public class MainActivity extends AppCompatActivity implements MyCanvas.PathsCha
 
     @OnClick(R.id.undo)
     public void undo() {
-        myCanvas.undo();
+        mMyCanvas.undo();
     }
 
     @OnClick(R.id.color_picker)
@@ -232,12 +237,12 @@ public class MainActivity extends AppCompatActivity implements MyCanvas.PathsCha
 
     private void setColor(int pickedColor) {
         color = pickedColor;
-        colorPicker.setBackgroundColor(color);
-        myCanvas.setColor(color);
+        mColorPicker.setBackgroundColor(color);
+        mMyCanvas.setColor(color);
     }
 
     @Override
     public void pathsChanged(int cnt) {
-        undoBtn.setVisibility(cnt > 0 ? View.VISIBLE : View.GONE);
+        mUndoBtn.setVisibility(cnt > 0 ? View.VISIBLE : View.GONE);
     }
 }