android自己写的类似刻度尺的东西

刚学android不久，因为公司项目要求，写了个类似刻度尺的东西，拿出来献丑，希望大家给点意见。

先上代码，注：KeduView中的浮点数计算我没处理（因为精度问题，浮点数直接计算出来的结果可能不对）。StaffView中的浮点数计算我进行了处理，我在Arithmetic中封装了加减乘除方法：
Java代码
package com.hyx.suiyipaint;

import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.Rect;
import android.os.Bundle;
import android.view.KeyEvent;
import android.view.MotionEvent;
import android.view.Su易做图ceHolder;
import android.view.Su易做图ceView;
import android.view.View;
import android.widget.ImageView;
import android.widget.LinearLayout;

public class KeduActivity extends Activity {

    private ImageView kedu_tiao;
    private LinearLayout kedu_linear;
    private LinearLayout staff_linear;

    private KeduView kedu;
    private StaffView staff;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.kedu);

        kedu_linear = (LinearLayout)findViewById(R.id.kedu_linear);
        kedu = new KeduView(this, 0f, 0.1f);
        kedu_linear.addView(kedu);
        staff_linear = (LinearLayout)findViewById(R.id.staff_linear);
        staff = new StaffView(this, 7.5f, 0.5f, "cm");
        staff_linear.addView(staff);

        kedu_tiao = (ImageView)findViewById(R.id.kedu_tiao);
        kedu_tiao.setOnTouchListener(keduListener);

    }

    private ImageView.OnTouchListener keduListener = new ImageView.OnTouchListener(){
        private float initx = 0;
        @Override
        public boolean onTouch(View v, MotionEvent event) {
            switch(event.getAction()){
                case MotionEvent.ACTION_DOWN:
                    initx = event.getX();
                    break;
                case MotionEvent.ACTION_MOVE:
                    float lastx = event.getX();
                    if(lastx > initx + 5){
                        kedu.draw(1);
                        initx = lastx;
                    }else if(lastx < initx -5){
                        kedu.draw(-1);
                        initx = lastx;
                    }
                    break;
            }
            return true;
        }
    };

    class KeduView extends Su易做图ceView implements Su易做图ceHolder.Callback, Runnable{

        private Su易做图ceHolder mSu易做图ceHolder = null;
        private Canvas canvas;
        //画布背景
        private Bitmap background;
        //刻度游标
        private Bitmap pointer;

        //总刻度数
        private static final int KEDU_COUNT = 25;
        //刻度最小值
        private float init_min;
        //每个刻度的单位值
        private float interval;

        public KeduView(Context context, float init_min, float interval) {
            super(context);
            mSu易做图ceHolder = this.getHolder();
            mSu易做图ceHolder.addCallback(this);
            this.setFocusable(true);
            background = BitmapFactory.decodeResource(getResources(), R.drawable.kedu_bg);
            pointer = BitmapFactory.decodeResource(getResources(), R.drawable.kedu_pointer);

            this.init_min = init_min;
       &n

补充：移动开发 , Android ,