android - Android NullPointerException 导致崩溃

Question

我正在创建一个安卓纸牌游戏。我创建了一个扑克牌类和一个纸牌类。当我运行示例代码时，它无法构建甲板。这是我的代码和 logcat

扑克牌.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;

}

}

启动屏幕.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);

}
}

主要的.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>

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 输出

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

score 1 · Accepted Answer

您正在cardArray正确地创建，但您没有用任何对PlayingCard. 在您将它们设置为某个值之前，它们都是空值。

score 0 · Accepted Answer

根据堆栈跟踪，有问题的行是：

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

在 CardDeck.java 中。

我猜这是因为该数组元素的内容为空。虽然您已经定义了数组，但在尝试对其元素调用 .setSuit(...) 之前，您似乎没有将任何对象放入其中 - 所以您在 null 上调用 .setSuit(...) -因此 NPE。

android - Android NullPointerException 导致崩溃

2 回答 2

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