Android NullPointerExceptionクラッシュの原因

Question

私はアンドロイドカードゲームを作成しています。私はトランプカードクラスとカードデッキクラスを作成しました。サンプルコードを実行すると、デッキを構築できません。ここに私のコードは、logcat

PlayingCard.java

package com.michaelpeerman.hi_low; 

public class PlayingCard { 
public String[] CardSuit = {"SPADE","HEART","CLUB","DIAMOND"}; 
public String[] CardRank= {"ACE", "TWO", "THREE", "FOUR", "FIVE", "SIX", "SEVEN", "EIGHT", "NINE","JACK","QUEEN","KING"}; 
public String theSuit; 
public int theRank; 
public boolean theState; 

public PlayingCard(){ 
    theSuit = "SPADE"; 
    theRank = 1; 
    theState = false; 
} 
public PlayingCard(String mySuit, int myRank){ 
    theSuit = mySuit; 
    theRank = myRank; 

} 
public int getRank(){ 
    return theRank; 

} 
public String getSuit(){ 
    return theSuit; 

} 
public boolean getState(){ 
    return theState; 

} 
public void setState(boolean myState){ 
    theState = myState; 
} 
public void setRank(int myRank){ 
    theRank = myRank; 
} 
public void setSuit(String mySuit){ 
    theSuit = mySuit; 
} 
public String getCardString(){ 
    String cardString = null; 
     String theCardRanks[] = {"A","2","3","4","5","6","7","8","9","T","J","Q","K"}; 

     if (theSuit == "CLUB") 
      cardString = "C"+theCardRanks[theRank-1]; 
     else if (theSuit == "SPADE") 
      cardString = "S"+theCardRanks[theRank-1]; 
     else if (theSuit == "HEART") 
      cardString = "H"+theCardRanks[theRank-1]; 
     else if (theSuit == "DIAMOND") 
      cardString = "D"+theCardRanks[theRank-1]; 
     return cardString; 
} 
} 

CardDeck.java

package com.michaelpeerman.hi_low; 
import java.util.Random; 

import com.michaelpeerman.hi_low.PlayingCard; 
public class CardDeck { 
public PlayingCard[] cardArray; 
public int num_decks; 
public int cards_left; 
public CardDeck(int my_decks) 
{ 
num_decks = my_decks; 
cardArray = new PlayingCard[52*num_decks]; 
cards_left = 52*num_decks; 
for (int i=0; i< num_decks; i++){ 
for (int j = 0; j < 13; j++) 
{ 

     cardArray[(j+(52*i))].setSuit("SPADE"); 
     cardArray[j+13+(52*i)].setSuit("HEART"); 
     cardArray[j+26+(52*i)].setSuit("CLUB"); 
     cardArray[j+39+(52*i)].setSuit("DIAMOND"); 




    if (j==0){ 
     cardArray[j+(52*i)].setRank(1); 
     cardArray[j+13+(52*i)].setRank(1); 
     cardArray[j+26+(52*i)].setRank(1); 
     cardArray[j+39+(52*i)].setRank(1); 
     } 
    else if (j==1){ 
     cardArray[j+(52*i)].setRank(2); 
     cardArray[j+13+(52*i)].setRank(2); 
     cardArray[j+26+(52*i)].setRank(2); 
     cardArray[j+39+(52*i)].setRank(2); 
     } 
    else if (j==2){ 
     cardArray[j+(52*i)].setRank(3); 
     cardArray[j+13+(52*i)].setRank(3); 
     cardArray[j+26+(52*i)].setRank(3); 
     cardArray[j+39+(52*i)].setRank(3); 
     } 
    else if (j==3){ 
     cardArray[j+(52*i)].setRank(4); 
     cardArray[j+13+(52*i)].setRank(4); 
     cardArray[j+26+(52*i)].setRank(4); 
     cardArray[j+39+(52*i)].setRank(4); 
     } 
    else if (j==4){ 
     cardArray[j+(52*i)].setRank(5); 
     cardArray[j+13+(52*i)].setRank(5); 
     cardArray[j+26+(52*i)].setRank(5); 
     cardArray[j+39+(52*i)].setRank(5); 
     } 
    else if (j==5){ 
     cardArray[j+(52*i)].setRank(6); 
     cardArray[j+13+(52*i)].setRank(6); 
     cardArray[j+26+(52*i)].setRank(6); 
     cardArray[j+39+(52*i)].setRank(6); 
     } 
    else if (j==6){ 
     cardArray[j+(52*i)].setRank(7); 
     cardArray[j+13+(52*i)].setRank(7); 
     cardArray[j+26+(52*i)].setRank(7); 
     cardArray[j+39+(52*i)].setRank(7); 
     } 
    else if (j==7){ 
     cardArray[j+(52*i)].setRank(8); 
     cardArray[j+13+(52*i)].setRank(8); 
     cardArray[j+26+(52*i)].setRank(8); 
     cardArray[j+39+(52*i)].setRank(8); 
     } 
    else if (j==8){ 
     cardArray[j+(52*i)].setRank(9); 
     cardArray[j+13+(52*i)].setRank(9); 
     cardArray[j+26+(52*i)].setRank(9); 
     cardArray[j+39+(52*i)].setRank(9); 
     } 
    else if (j==9){ 
     cardArray[j+(52*i)].setRank(10); 
     cardArray[j+13+(52*i)].setRank(10); 
     cardArray[j+26+(52*i)].setRank(10); 
     cardArray[j+39+(52*i)].setRank(10); 
     } 
    else if (j==10){ 
     cardArray[j+(52*i)].setRank(11); 
     cardArray[j+13+(52*i)].setRank(11); 
     cardArray[j+26+(52*i)].setRank(11); 
     cardArray[j+39+(52*i)].setRank(11); 
     } 
    else if (j==11){ 
     cardArray[j+(52*i)].setRank(12); 
     cardArray[j+13+(52*i)].setRank(12); 
     cardArray[j+26+(52*i)].setRank(12); 
     cardArray[j+39+(52*i)].setRank(12); 
     } 
    else if (j==12){ 
     cardArray[j+(52*i)].setRank(13); 
     cardArray[j+13+(52*i)].setRank(13); 
     cardArray[j+26+(52*i)].setRank(13); 
     cardArray[j+39+(52*i)].setRank(13); 
     } 

} 
} 
} 
public void useCard(){ 
cards_left = cards_left - 1; 
} 
public int get_cards_left(){ 
return cards_left; 
} 
public void setCard(int card, PlayingCard myCard){ 
cardArray[card]=myCard; 

} 

public PlayingCard getCard(int card){ 

return cardArray[card]; 

} 

public void printDeck(){ 
for (int j = 0; j < (52*num_decks); j++){ 
    // Print out to textview 
    //String cardString = cardArray[j].getCardString(); 
} 

} 
public void suffleDeck(){ 

for (int i = 0; i < 100*num_decks; i++) 
{ 
    int rand1 = 1 + new Random().nextInt(52*num_decks); 
    int rand2 = 1 + new Random().nextInt(52*num_decks); 
    PlayingCard tmpCard = cardArray[rand1]; 
    cardArray[rand1] = cardArray[rand2]; 
    cardArray[rand2] = tmpCard; 
} 
} 
public boolean isDeckFinished(){ 
boolean isFinished =true; 
for (int i = 0; i<52*num_decks; i++){ 
    PlayingCard myCard = cardArray[i]; 
    if (myCard.getState() == false){ 
     isFinished = false; 
    } 
} 
return isFinished; 

} 

} 

StartScreen.java

package com.michaelpeerman.hi_low; 

import android.app.Activity; 
import android.os.Bundle; 
import android.widget.TextView; 
import com.michaelpeerman.hi_low.R; 
import com.michaelpeerman.hi_low.CardDeck; 
import com.michaelpeerman.hi_low.PlayingCard; 

public class StartScreen extends Activity { 
/** Called when the activity is first created. */ 
@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.main); 
    CardDeck myDeck = new CardDeck(1); 
    int cards = myDeck.cards_left; 
    String text = Integer.toString(cards); 
    TextView t=new TextView(this); 

    t=(TextView)findViewById(R.id.main_text); 
    t.append(text); 

} 
} 

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" > 
<ScrollView 
android:layout_width="fill_parent" 
android:layout_height="fill_parent"> 
<TextView 
    android:id="@+id/main_text" 
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    /> 
</ScrollView> 
</LinearLayout> 

とともにあります

のAndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?> 
<manifest xmlns:android="http://schemas.android.com/apk/res/android" 
package="com.michaelpeerman.hi_low" 
android:versionCode="1" 
android:versionName="1.0" > 

<uses-sdk android:minSdkVersion="13" /> 

<application 
    android:icon="@drawable/ic_launcher" 
    android:label="@string/app_name" > 
    <activity 
     android:name=".StartScreen" 
     android:label="@string/app_name" > 
     <intent-filter> 
      <action android:name="android.intent.action.MAIN" /> 

      <category android:name="android.intent.category.LAUNCHER" /> 
     </intent-filter> 
    </activity> 
</application> 

</manifest> 

LogCat出力

05-03 18:03:55.067: E/AndroidRuntime(9805): FATAL EXCEPTION: main 
05-03 18:03:55.067: E/AndroidRuntime(9805): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.michaelpeerman.hi_low/com.michaelpeerman.hi_low.StartScreen}: java.lang.NullPointerException 
05-03 18:03:55.067: E/AndroidRuntime(9805):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956) 
05-03 18:03:55.067: E/AndroidRuntime(9805):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981) 
05-03 18:03:55.067: E/AndroidRuntime(9805):  at android.app.ActivityThread.access$600(ActivityThread.java:123) 
05-03 18:03:55.067: E/AndroidRuntime(9805):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147) 
05-03 18:03:55.067: E/AndroidRuntime(9805):  at android.os.Handler.dispatchMessage(Handler.java:99) 
05-03 18:03:55.067: E/AndroidRuntime(9805):  at android.os.Looper.loop(Looper.java:137) 
05-03 18:03:55.067: E/AndroidRuntime(9805):  at android.app.ActivityThread.main(ActivityThread.java:4424) 
05-03 18:03:55.067: E/AndroidRuntime(9805):  at java.lang.reflect.Method.invokeNative(Native Method) 
05-03 18:03:55.067: E/AndroidRuntime(9805):  at java.lang.reflect.Method.invoke(Method.java:511) 
05-03 18:03:55.067: E/AndroidRuntime(9805):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) 
05-03 18:03:55.067: E/AndroidRuntime(9805):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551) 
05-03 18:03:55.067: E/AndroidRuntime(9805):  at dalvik.system.NativeStart.main(Native Method) 
05-03 18:03:55.067: E/AndroidRuntime(9805): Caused by: java.lang.NullPointerException 
05-03 18:03:55.067: E/AndroidRuntime(9805):  at com.michaelpeerman.hi_low.CardDeck.<init>(CardDeck.java:18) 
05-03 18:03:55.067: E/AndroidRuntime(9805):  at com.michaelpeerman.hi_low.StartScreen.onCreate(StartScreen.java:16) 
05-03 18:03:55.067: E/AndroidRuntime(9805):  at android.app.Activity.performCreate(Activity.java:4465) 
05-03 18:03:55.067: E/AndroidRuntime(9805):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049) 
05-03 18:03:55.067: E/AndroidRuntime(9805):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920) 
05-03 18:03:55.067: E/AndroidRuntime(9805):  ... 11 more 

Answer 1

あなたが適切にcardArrayを作成しているが、あなたはPlayingCardへの参照とそれを充填していません。あなたが何かに設定するまで、彼らはすべてnullです。

Answer 2

は、スタックトレースによると、問題の行は次のようになります。CardDeck.javaで

cardArray[(j+(52*i))].setSuit("SPADE"); 

。

配列の要素の内容がnullであることが原因であると推測しています。配列を定義している間に、その要素上で.setSuit（...）を呼び出そうとする前に、配列にオブジェクトを置くようには見えないので、ヌルで.setSuit（...）したがってNPE。