FloatingActionButton.java

package  your_package;

import android.animation.AnimatorSet;
import android.animation.ObjectAnimator;
import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.drawable.BitmapDrawable;
import android.graphics.drawable.Drawable;
import android.view.Gravity;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.view.animation.AccelerateInterpolator;
import android.view.animation.OvershootInterpolator;
import android.widget.FrameLayout;

public class FloatingActionButton extends View {
  Context context;
  Paint mButtonPaint;
  Paint mDrawablePaint;
  Bitmap mBitmap;
  boolean mHidden = false;

  public FloatingActionButton(Context context) {
    super(context);
    this.context = context;
    init(Color.WHITE);
  }

  public void setFloatingActionButtonColor(int FloatingActionButtonColor) {
    init(FloatingActionButtonColor);
  }

  public void setFloatingActionButtonDrawable(Drawable FloatingActionButtonDrawable) {
    mBitmap = ((BitmapDrawable) FloatingActionButtonDrawable).getBitmap();
    invalidate();
  }

  public void init(int FloatingActionButtonColor) {
    setWillNotDraw(false);
    setLayerType(View.LAYER_TYPE_SOFTWARE, null);

    mButtonPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    mButtonPaint.setColor(FloatingActionButtonColor);
    mButtonPaint.setStyle(Paint.Style.FILL);
    mButtonPaint.setShadowLayer(10.0f, 0.0f, 3.5f, Color.argb(100, 0, 0, 0));
    mDrawablePaint = new Paint(Paint.ANTI_ALIAS_FLAG);

    invalidate();
  }

  @Override
  protected void onDraw(Canvas canvas) {
    setClickable(true);
    canvas.drawCircle(getWidth() / 2, getHeight() / 2, (float) (getWidth() / 2.6), mButtonPaint);
    canvas.drawBitmap(mBitmap, (getWidth() - mBitmap.getWidth()) / 2,
        (getHeight() - mBitmap.getHeight()) / 2, mDrawablePaint);
  }

  @Override
  public boolean onTouchEvent(MotionEvent event) {
    if (event.getAction() == MotionEvent.ACTION_UP) {
      setAlpha(1.0f);
    } else if (event.getAction() == MotionEvent.ACTION_DOWN) {
      setAlpha(0.6f);
    }
    return super.onTouchEvent(event);
  }

  public void hideFloatingActionButton() {
    if (!mHidden) {
      ObjectAnimator scaleX = ObjectAnimator.ofFloat(this, "scaleX", 1, 0);
      ObjectAnimator scaleY = ObjectAnimator.ofFloat(this, "scaleY", 1, 0);
      AnimatorSet animSetXY = new AnimatorSet();
      animSetXY.playTogether(scaleX, scaleY);
      animSetXY.setInterpolator(new AccelerateInterpolator());
      animSetXY.setDuration(100);
      animSetXY.start();
      mHidden = true;
    }
  }

  public void showFloatingActionButton() {
    if (mHidden) {
      ObjectAnimator scaleX = ObjectAnimator.ofFloat(this, "scaleX", 0, 1);
      ObjectAnimator scaleY = ObjectAnimator.ofFloat(this, "scaleY", 0, 1);
      AnimatorSet animSetXY = new AnimatorSet();
      animSetXY.playTogether(scaleX, scaleY);
      animSetXY.setInterpolator(new OvershootInterpolator());
      animSetXY.setDuration(200);
      animSetXY.start();
      mHidden = false;
    }
  }

  public boolean isHidden() {
    return mHidden;
  }

  static public class Builder {
    private FrameLayout.LayoutParams params;
    private final Activity activity;
    int gravity = Gravity.BOTTOM | Gravity.RIGHT; // default bottom right
    Drawable drawable;
    int color = Color.WHITE;
    int size = 0;
    float scale = 0;

    public Builder(Activity context) {
      scale = context.getResources().getDisplayMetrics().density;
      // The calculation (value * scale + 0.5f) is a widely used to convert to dps to pixel units
      // based on density scale
      // see developer.android.com (Supporting Multiple Screen Sizes)
      size = (int) (72 * scale + 0.5f); // default size is 72dp by 72dp
      params = new FrameLayout.LayoutParams(size, size);
      params.gravity = gravity;

      this.activity = context;
    }

    /**
     * Sets the gravity for the FAB
     */
    public Builder withGravity(int gravity) {
      this.gravity = gravity;
      return this;
    }

    /**
     * Sets the margins for the FAB in dp
     */
    public Builder withMargins(int left, int top, int right, int bottom) {
      params.setMargins((int) (left * scale + 0.5f), (int) (top * scale + 0.5f),
          (int) (right * scale + 0.5f), (int) (bottom * scale + 0.5f));
      return this;
    }

    /**
     * Sets the FAB drawable
     */
    public Builder withDrawable(final Drawable drawable) {
      this.drawable = drawable;
      return this;
    }

    /**
     * Sets the FAB color
     */
    public Builder withButtonColor(final int color) {
      this.color = color;
      return this;
    }

    /**
     * Sets the FAB size in dp
     */
    public Builder withButtonSize(int size) {
      size = (int) (size * scale + 0.5f);
      params = new FrameLayout.LayoutParams(size, size);
      return this;
    }

    public FloatingActionButton create() {
      final FloatingActionButton button = new FloatingActionButton(activity);
      button.setFloatingActionButtonColor(this.color);
      button.setFloatingActionButtonDrawable(this.drawable);
      params.gravity = this.gravity;
      ViewGroup root = (ViewGroup) activity.findViewById(android.R.id.content);
      root.addView(button, params);
      return button;
    }
  }
}

HowToAdd.java

FloatingActionButton fabButton = new FloatingActionButton.Builder(this)
        .withDrawable(getResources().getDrawable(R.drawable.ic_action_add))
        .withButtonColor(Color.WHITE)
        .withGravity(Gravity.BOTTOM | Gravity.RIGHT)
        .withMargins(0, 0, 16, 16)
        .create();