4.8.模拟硬币投掷

4.8. 模拟硬币投掷

问题
我要模拟硬币投掷或布尔事件来达到50%几率成功。
解决办法
用NumberUtilities.random( ) 方法产生 0 到 1的整数，根据每种可能得出结果。
讨论

用 random( ) 方法产生指定范围的随机整数，能够产生两个结果对应硬币的正面和反面状态，在程序里我们用0代表一个状态，1代表另一状态，当然你用1和2也是可以的，总之是2个状态，这样就能模拟硬币投掷了：

package ...{

import flash.display.Sprite;
import flash.text.TextField;
import flash.events.MouseEvent;
import ascb.util.NumberUtilities;

public class CoinExample extends Sprite ...{

private var _field:TextField;

public function CoinExample( ) ...{
_field = new TextField( );
_field.autoSize = "left";
addChild(_field);
var circle:Sprite = new Sprite( );
circle.graphics.beginFill(0, 100);
circle.graphics.drawCircle(100, 100, 100);
circle.graphics.endFill( );
circle.addEventListener(MouseEvent.CLICK, onClick);
addChild(circle);
}

private function onClick(event:MouseEvent):void ...{
var randomNumber:Number = NumberUtilities.random(0, 1);
_field.text = (randomNumber == 0) ? "heads" : "tails";
}

}
}

记录正反面出现次数：

package ...{

import flash.display.Sprite;
import flash.text.TextField;
import ascb.util.NumberUtilities;

public class CoinTest extends Sprite ...{

private var _field:TextField;

public function CoinTest( ) ...{
_field = new TextField( );
_field.autoSize = "left";
addChild(_field);
var heads:Number = 0;
var tails:Number = 0;
var randomNumber:Number;
for(var i:Number = 0; i < 10000; i++) ...{
randomNumber = NumberUtilities.random(0, 1);
if(randomNumber == 0) ...{
heads++;
}
else ...{
tails++;
}
}
_field.text = "heads: " + heads + ", tails: " + tails;
}

}
}

如果要测试随机数，应该保存在变量中，像上面的代码，下面代码的统计是错误的，因此else if每次都产生新的随机数：

package ...{

import flash.display.Sprite;
import ascb.util.NumberUtilities;

public class RandomLetter extends Sprite ...{

public function RandomLetter( ) ...{
for(var i:Number = 0; i < 10000; i++) ...{
trace(getRandomLetter( ));
}
}

private function getRandomLetter( ):String ...{
if(NumberUtilities.random(0, 2) == 0) ...{
return "A";
}
else if(NumberUtilities.random(0, 2) == 1) ...{
return "B";
}
else if(NumberUtilities.random(0, 2) == 2) ...{
return "C";
}
// It's possible that none of the preceding will evaluate to true,
// and the method will reach this point without returning a valid
// string.
return "";
}
}
}

下面才正确：

package ...{

import flash.display.Sprite;
import ascb.util.NumberUtilities;

public class RandomLetter extends Sprite ...{

public function RandomLetter( ) ...{
for(var i:uint = 0; i < 10000; i++) ...{
trace(getRandomLetter( ));
}
}

private function getRandomLetter( ):String ...{
// random( ) 返回结果到变量上
var randomInteger:uint = NumberUtilities.random(0, 2);
if(randomInteger == 0) ...{
return "A";
}
else if(randomInteger == 1) ...{
return "B";
}
else if(randomInteger == 2) ...{
return "C";
}
return "";
}
}
}