作者：黑洞
前几天看到mathfp的文章，很有些激动，
有了浮点数很多不能做的事情都变为可能。
但是一大堆MathFP开头的函数和不断的转换让人头大。
于是就想着自己封装一下，很多人都有这个想法吧：）
我的这个叫做Float。
1。首先是浮点常数，这个没什么好说的
public static final Float PI = new Float(MathFP.PI); public static final Float E = new Float(MathFP.E); public static final Float pi2 = PI.div(2); public static final Float pi4 = PI.div(4); public static final Float pi = PI.div(180); //PI/180 public static final Float neg1 = new Float( -1); //-1 public static final Float pos1 = new Float(1); //+1 public static final Float ln10 = new Float(10).ln_s(); public static final Float zero = new Float(0);
2。字段和构造函数
long v;
public Float(Float f) {
v = f.v;
}
public Float(String val) {
v = MathFP.toFP(val);
}
public Float(int val) {
v = MathFP.toFP(val);
}
private Float(long val) {
v = val;
}
最后一个构造函数相当与clone的意思。
3。函数的封装（我把基本运算也归到里面了）
一开始我是这么做的，比如add函数：
public Float add(Float b) {
return new Float(MathFP.add(v, b.v));
}
public Float add(int b) {
return new Float(MathFP.add(v, MathFP.toFP(b)));
}
大家看出什么问题来了吗？
如果要做一个x+1+2+3+4的运算，通过调用x.add(1).add(2).add(3).add(4)
将会生成4个Float对象，而其中的3个Float对象用过就扔掉了。
这使gc的负担飚升。于是我增加了这样一个方法：
public Float add_s(Float b) {
v = MathFP.add(v, b.v);
return this;
}
相当于+=的功能，于是可以调用x.add(1).add_s(2).add_s(3).add_s(4)来实现
这样就节省了3个Float的开销。其他的函数类推就不罗索了，下面看看FloatBox。
既然有了浮点数，我们如何输入呢？文本框有数字模式但是不支持浮点数，
用any模式？这样太不专业了，于是就有了FloatBox。
这就是整个实现：
package vmlinux.math;
import javax.microedition.lcdui.*;
import vmlinux.app.*;
public class FloatBox extends Canvas {
public static final String[] Keypad = new String[] {
"1", "2", "3",
"4", "5", "6",
"7", "8", "9",
".", "0", "+/-"
};
public Command Done;
public Command Cancel;
public Command Delete;
StringBuffer val_;
boolean dot_;
Image imgKeypad_;
char c_;
public FloatBox(CommandListener o) {
Cancel = new Command(StringManager.get("FloatBox.Cancel"),
Command.SCREEN, 3);
Done = new Command(StringManager.get("FloatBox.Done"), Command.SCREEN,
2);
Delete = new Command(StringManager.get("FloatBox.Delete"),
Command.SCREEN, 1);
this.addCommand(Cancel);
this.addCommand(Done);
this.addCommand(Delete);
this.setCommandListener(o);
val_ = new StringBuffer("0");
dot_ = false;
}
protected void paint(Graphics g) {
g.setColor(0xff, 0xff, 0xff);
g.fillRect(0, 0, getWidth(), getHeight());
g.setColor(0x00, 0x00, 0x00);
g.drawRect(5, 5, getWidth() - 10, 30);
g.setColor(0x00, 0x00, 0xff);
g.drawString(val_.toString(), getWidth() - 10, 10,
Graphics.TOP | Graphics.RIGHT);
drawKeypad(Keypad, 40, g, c_);
}
void drawKeypad(String[] keys, int ytake, Graphics gx, char chr) {
int xs = getWidth() / 3;
int ys = (getHeight() - ytake) / 4;
int hcenter = Graphics.TOP | Graphics.HCENTER;
if (imgKeypad_ == null) {
imgKeypad_ = Image.createImage(getWidth(), getHeight() - ytake);
Graphics g = imgKeypad_.getGraphics();
int c = 0;
for (int j = 0; j < 4; ++j) {
for (int i = 0; i < 3; ++i) {
g.setColor(0xcc, 0xcc, 0xcc);
g.drawRect((xs + 1) * i, (ys + 1) * j, xs - 2, ys - 2);
if (c < keys.length) {
g.setColor(0x00, 0x00, 0x00);
g.drawString(keys[c++], xs * i + xs / 2 - 2,
ys * j + ys / 2 - 8, hcenter);
}
}
}
}
gx.drawImage(imgKeypad_, 0, ytake, Graphics.TOP | Graphics.LEFT);
for (int i = 0; i < keys.length; ++i) {
if (keys[i].indexOf(chr) >= 0) {
gx.setColor(0xbb, 0xbb, 0xbb);
gx.fillRect((xs + 1) * (i % 3), (ys + 1) * (i / 3) + ytake,
xs - 2, ys - 2);
gx.setColor(0xff, 0xff, 0xff);
gx.drawString(keys[i], xs * (i % 3) + xs / 2,
ys * (i / 3) + ytake + ys / 2 - 5, hcenter);
break;
}
}
}
protected void keyPressed(int key) {
if (key == Canvas.KEY_NUM0) {
if (val_.length() == 0 ||
(val_.length() > 0 && val_.charAt(0) != '0')) {
val_.append('0');
}
c_ = '0';
} else if (key >= Canvas.KEY_NUM1 && key <= Canvas.KEY_NUM9) {
char c = (char) ('1' + key - Canvas.KEY_NUM1);
if (val_.length() == 1 && val_.charAt(0) == '0') {
val_.deleteCharAt(0);
val_.append(c);
} else {
val_.append(c);
}
c_ = c;
} else if (key == Canvas.KEY_STAR) {
if (!dot_) {
val_.append('.');
dot_ = true;
}
c_ = '.';
} else if (key == Canvas.KEY_POUND) {
if (val_.length() > 0 && val_.charAt(0) == '-') {
val_.deleteCharAt(0);
} else if (val_.length() != 1 || val_.charAt(0) != '0') {
val_.insert(0, '-');
}
c_ = '-';
} else if (this.getGameAction(key) == Canvas.LEFT) {
delete();
}
repaint();
}
public void delete() {
if (val_.length() > 0) {
if (val_.charAt(val_.length() - 1) == '.') {
dot_ = false;
}
val_.deleteCharAt(val_.length() - 1);
if (val_.length() == 1 && val_.charAt(0) == '-') {
val_.deleteCharAt(0);
}
}
if (val_.length() == 0) {
val_.append('0');
}
}
public Float getValue() {
return new Float(val_.toString());
}
public void setValue(Float x) {
val_.delete(0, val_.length());
val_.append(x.toString());
}
}没什么难度，不多说了。StringManager参见我的另一篇字符串管理的文章。
样子很丑，看起来就像一个计算器。
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