關於pseudo-random

如果你運行前文的"Android 的隨機數字產生器", 你會發現若你選擇Random(long seed), 與及使用相同的seek, 其所產生的數字是相同的. 這是因為該應用程序每次只產生第一個生成的數字, 而所謂pseudo-random並不是真正的隨機, 而是按照一定的算法產生類似隨機的數字.

接下來, 改動一下代碼, 將有更明確的理解. 這裡有兩個Activity, 第一個AndroidRandom選擇constructor和seek, 第二個RunRandom從而建構一個隨機數字產生器, 如果繼續點擊便會繼續產生下一個隨機數字.




main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
<TextView  
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:text="@string/hello"
    />
<RadioGroup
 android:layout_width="fill_parent"
 android:layout_height="wrap_content"
 android:checkedButton="@+id/milliseconds"
 android:id="@+id/contructor" >
<RadioButton
 android:text="Random()"
 android:id="@+id/milliseconds" />
<RadioButton
 android:text="Random(long seed)"
 android:id="@+id/seed" />
</RadioGroup>
<EditText
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   android:inputType="number"
   android:id="@+id/seeknumber"
 />
<Button
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   android:text="Construct a Random Generate"
   android:id="@+id/construct"
 />
</LinearLayout>

AndroidRandom.java

package com.AndroidRandom;

import java.util.Random;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.RadioButton;
import android.widget.TextView;

public class AndroidRandom extends Activity {
 
    RadioButton rbRandomMilliseconds, rbRandomSeek;
    EditText etSeekNumber;
    Button buttonConstruct;
 
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        rbRandomMilliseconds = (RadioButton)findViewById(R.id.milliseconds);
        rbRandomSeek = (RadioButton)findViewById(R.id.seed);
        etSeekNumber = (EditText)findViewById(R.id.seeknumber);
        buttonConstruct = (Button)findViewById(R.id.construct);
        
        buttonConstruct.setOnClickListener(buttonConstructOnClickListener);
    }
    
    private Button.OnClickListener buttonConstructOnClickListener 
     = new Button.OnClickListener(){

   @Override
   public void onClick(View v) {
    
    String strTypeOfConstructor, strInitSeek;
    
    // TODO Auto-generated method stub
    if (rbRandomMilliseconds.isChecked()){
     strTypeOfConstructor = "RandomMilliseconds";
    }
    else{
     strTypeOfConstructor = "RandomSeek";
    }
    
    strInitSeek = etSeekNumber.getText().toString();
    
    Intent intent = new Intent(AndroidRandom.this,RunRandom.class);
    Bundle bundle = new Bundle();
    bundle.putString("keyTypeOfConstructor", strTypeOfConstructor);
    bundle.putString("keyInitSeek", strInitSeek);
    intent.putExtras(bundle);
    startActivity(intent);
 
   }
     
    };
    
}

runrandom.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
<TextView  
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:id="@+id/typeofconstructor"
    />
<RadioGroup
 android:layout_width="fill_parent"
 android:layout_height="wrap_content"
 android:checkedButton="@+id/typeint"
 android:id="@+id/type" >
<RadioButton
 android:text="int"
 android:id="@+id/typeint" />
<RadioButton
 android:text="long"
 android:id="@+id/typelong" />
<RadioButton
 android:text="double"
 android:id="@+id/typedouble" />
<RadioButton
 android:text="float"
 android:id="@+id/typefloat" />
</RadioGroup>
<Button
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   android:text="Generate Random number"
   android:id="@+id/generate"
 />
<TextView
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   android:id="@+id/generatednumber"
 />
</LinearLayout>

RunRandom.java

package com.AndroidRandom;

import java.util.Random;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.RadioButton;
import android.widget.TextView;

public class RunRandom extends Activity {

    TextView tvTypeofconstructor;
    RadioButton rbInt, rbLong, rbDouble, rbFloat;
    Button buttonGenerate;
    TextView textGeneratedNumber;

    
    
    Long initSeek;
    Random myRandom;
 
 @Override
 protected void onCreate(Bundle savedInstanceState) {
  // TODO Auto-generated method stub
  super.onCreate(savedInstanceState);
  setContentView(R.layout.runrandom);
  tvTypeofconstructor = (TextView)findViewById(R.id.typeofconstructor);
        rbInt = (RadioButton)findViewById(R.id.typeint);
        rbLong = (RadioButton)findViewById(R.id.typelong);
        rbDouble = (RadioButton)findViewById(R.id.typedouble);
        rbFloat = (RadioButton)findViewById(R.id.typefloat);
        buttonGenerate = (Button)findViewById(R.id.generate);
        textGeneratedNumber = (TextView)findViewById(R.id.generatednumber);
        
        buttonGenerate.setOnClickListener(buttonGenerateOnClickListener);
        
        
        Bundle bundle = this.getIntent().getExtras();
        String typeOfConstructor = bundle.getString("keyTypeOfConstructor");
        String strInitSeek = bundle.getString("keyInitSeek");
        
        if (typeOfConstructor.equals("RandomMilliseconds")){
         tvTypeofconstructor.setText("Random()");
   myRandom = new Random();
  }
  else{
   Long tSeek;
   if (strInitSeek.equals(""))
   {
    tvTypeofconstructor.setText("Random(0)");
    tSeek = 0L;
   }
   else
   {
    tvTypeofconstructor.setText("Random(" + strInitSeek + ")");
    tSeek = Long.decode(strInitSeek);
   }
   myRandom = new Random(tSeek);
  }
 }

 private Button.OnClickListener buttonGenerateOnClickListener 
 = new Button.OnClickListener(){

  @Override
  public void onClick(View v) {
   
   if (rbInt.isChecked()){
    textGeneratedNumber.setText(String.valueOf(myRandom.nextInt()));
   }
   else if (rbLong.isChecked()){
    textGeneratedNumber.setText(String.valueOf(myRandom.nextLong()));
   }
   else if (rbDouble.isChecked()){
    textGeneratedNumber.setText(String.valueOf(myRandom.nextDouble()));
   }
   else{
    textGeneratedNumber.setText(String.valueOf(myRandom.nextFloat()));
   }    
  }
 
 };
}

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
      package="com.AndroidRandom"
      android:versionCode="1"
      android:versionName="1.0">
    <application android:icon="@drawable/icon" android:label="@string/app_name">
        <activity android:name=".AndroidRandom"
                  android:label="@string/app_name">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
 <activity android:name=".RunRandom"></activity>
    </application>
    <uses-sdk android:minSdkVersion="4" />
</manifest>