Code Fragmen-重载的方法，参数少的去调用参数多的。

对于重载的方法，可以使用参数少的去调用参数多的（多出来的参数，使用默认值代替）。

• 代码的重用性，减少了冗余的code
• 单需要改动的时候，只需要改动参数最多的实现，而不是改动每一个方法实现。
• 无论从代码规模还是清晰度，都有很大提高。

一个例子：

public class CellLayout extends ViewGroup {

    public CellLayout(Context context) {
        this(context, null);
    }

    public CellLayout(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public CellLayout(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);

        // A ViewGroup usually does not draw, but CellLayout needs to draw a rectangle to show
        // the user where a dragged item will land when dropped.
        setWillNotDraw(false);

        TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.CellLayout, defStyle, 0);

        mOriginalCellWidth =
            mCellWidth = a.getDimensionPixelSize(R.styleable.CellLayout_cellWidth, 10);
        mOriginalCellHeight =
            mCellHeight = a.getDimensionPixelSize(R.styleable.CellLayout_cellHeight, 10);
        mWidthGap = mOriginalWidthGap = a.getDimensionPixelSize(R.styleable.CellLayout_widthGap, 0);
        mHeightGap = mOriginalHeightGap = a.getDimensionPixelSize(R.styleable.CellLayout_heightGap, 0);
        mMaxGap = a.getDimensionPixelSize(R.styleable.CellLayout_maxGap, 0);
        mCountX = LauncherModel.getCellCountX();
        mCountY = LauncherModel.getCellCountY();
        mOccupied = new boolean[mCountX][mCountY];

        a.recycle();

        setAlwaysDrawnWithCacheEnabled(false);

        final Resources res = getResources();

        mNormalBackground = res.getDrawable(R.drawable.homescreen_blue_normal_holo);
        mActiveGlowBackground = res.getDrawable(R.drawable.homescreen_blue_strong_holo);

        mOverScrollLeft = res.getDrawable(R.drawable.overscroll_glow_left);
        mOverScrollRight = res.getDrawable(R.drawable.overscroll_glow_right);
        mForegroundPadding =
                res.getDimensionPixelSize(R.dimen.workspace_overscroll_drawable_padding);

        mNormalBackground.setFilterBitmap(true);
        mActiveGlowBackground.setFilterBitmap(true);

        // Initialize the data structures used for the drag visualization.

        mCrosshairsDrawable = res.getDrawable(R.drawable.gardening_crosshairs);
        mEaseOutInterpolator = new DecelerateInterpolator(2.5f); // Quint ease out

        // Set up the animation for fading the crosshairs in and out
        int animDuration = res.getInteger(R.integer.config_crosshairsFadeInTime);
        mCrosshairsAnimator = new InterruptibleInOutAnimator(animDuration, 0.0f, 1.0f);
        mCrosshairsAnimator.getAnimator().addUpdateListener(new AnimatorUpdateListener() {
            public void onAnimationUpdate(ValueAnimator animation) {
                mCrosshairsVisibility = ((Float) animation.getAnimatedValue()).floatValue();
                invalidate();
            }
        });
        mCrosshairsAnimator.getAnimator().setInterpolator(mEaseOutInterpolator);

        mDragCell[0] = mDragCell[1] = -1;
        for (int i = 0; i < mDragOutlines.length; i++) {
            mDragOutlines[i] = new Point(-1, -1);
        }

        // When dragging things around the home screens, we show a green outline of
        // where the item will land. The outlines gradually fade out, leaving a trail
        // behind the drag path.
        // Set up all the animations that are used to implement this fading.
        final int duration = res.getInteger(R.integer.config_dragOutlineFadeTime);
        final float fromAlphaValue = 0;
        final float toAlphaValue = (float)res.getInteger(R.integer.config_dragOutlineMaxAlpha);

        Arrays.fill(mDragOutlineAlphas, fromAlphaValue);

        for (int i = 0; i < mDragOutlineAnims.length; i++) {
            final InterruptibleInOutAnimator anim =
                new InterruptibleInOutAnimator(duration, fromAlphaValue, toAlphaValue);
            anim.getAnimator().setInterpolator(mEaseOutInterpolator);
            final int thisIndex = i;
            anim.getAnimator().addUpdateListener(new AnimatorUpdateListener() {
                public void onAnimationUpdate(ValueAnimator animation) {
                    final Bitmap outline = (Bitmap)anim.getTag();

                    // If an animation is started and then stopped very quickly, we can still
                    // get spurious updates we've cleared the tag. Guard against this.
                    if (outline == null) {
                        if (false) {
                            Object val = animation.getAnimatedValue();
                            Log.d(TAG, "anim " + thisIndex + " update: " + val +
                                     ", isStopped " + anim.isStopped());
                        }
                        // Try to prevent it from continuing to run
                        animation.cancel();
                    } else {
                        mDragOutlineAlphas[thisIndex] = (Float) animation.getAnimatedValue();
                        final int left = mDragOutlines[thisIndex].x;
                        final int top = mDragOutlines[thisIndex].y;
                        CellLayout.this.invalidate(left, top,
                                left + outline.getWidth(), top + outline.getHeight());
                    }
                }
            });
            // The animation holds a reference to the drag outline bitmap as long is it's
            // running. This way the bitmap can be GCed when the animations are complete.
            anim.getAnimator().addListener(new AnimatorListenerAdapter() {
                @Override
                public void onAnimationEnd(Animator animation) {
                    if ((Float) ((ValueAnimator) animation).getAnimatedValue() == 0f) {
                        anim.setTag(null);
                    }
                }
            });
            mDragOutlineAnims[i] = anim;
        }

        mBackgroundRect = new Rect();
        mForegroundRect = new Rect();

        mChildren = new CellLayoutChildren(context);
        mChildren.setCellDimensions(mCellWidth, mCellHeight, mWidthGap, mHeightGap);
        addView(mChildren);
    }
    ....
}