Evorlor Evorlor -4 years ago 97
Java Question

Sorting Object with Comparator gives Null Pointer

I am trying sort the ArrayList with 3 Card in it. I am doing this with a Comparator. (Is this overkill)? Card.getRank() returns an integer between 2 and 14. I have absolutely no idea where I am going wrong. I have done this successfully before, and compared with my other code, and it seems the same. I would greatly appreciate if someone could spread some light on this!

public int getHand(Card c1, Card c2, Card c3) {

ArrayList<Card> hand = new ArrayList<Card>();
hand.add(c1);
hand.add(c2);
hand.add(c3);

Collections.sort(hand, new SortCards());





package com.evorlor.threecardpoker;

import java.util.Comparator;

public class SortCards implements Comparator<Card> {

@Override
public int compare(Card card1, Card card2) {

if ((card1.getRank() - card2.getRank()) > 0) {
return 1;
}
if ((card1.getRank() - card2.getRank()) < 0) {
return -1;
}
return 0;

}

}





LOGCAT:

08-06 18:32:56.155: E/AndroidRuntime(4906): FATAL EXCEPTION: main
08-06 18:32:56.155: E/AndroidRuntime(4906): java.lang.IllegalStateException: Could not execute method of the activity
08-06 18:32:56.155: E/AndroidRuntime(4906): at android.view.View$1.onClick(View.java:3599)
08-06 18:32:56.155: E/AndroidRuntime(4906): at android.view.View.performClick(View.java:4204)
08-06 18:32:56.155: E/AndroidRuntime(4906): at android.view.View$PerformClick.run(View.java:17355)
08-06 18:32:56.155: E/AndroidRuntime(4906): at android.os.Handler.handleCallback(Handler.java:725)
08-06 18:32:56.155: E/AndroidRuntime(4906): at android.os.Handler.dispatchMessage(Handler.java:92)
08-06 18:32:56.155: E/AndroidRuntime(4906): at android.os.Looper.loop(Looper.java:137)
08-06 18:32:56.155: E/AndroidRuntime(4906): at android.app.ActivityThread.main(ActivityThread.java:5041)
08-06 18:32:56.155: E/AndroidRuntime(4906): at java.lang.reflect.Method.invokeNative(Native Method)
08-06 18:32:56.155: E/AndroidRuntime(4906): at java.lang.reflect.Method.invoke(Method.java:511)
08-06 18:32:56.155: E/AndroidRuntime(4906): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
08-06 18:32:56.155: E/AndroidRuntime(4906): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
08-06 18:32:56.155: E/AndroidRuntime(4906): at dalvik.system.NativeStart.main(Native Method)
08-06 18:32:56.155: E/AndroidRuntime(4906): Caused by: java.lang.reflect.InvocationTargetException
08-06 18:32:56.155: E/AndroidRuntime(4906): at java.lang.reflect.Method.invokeNative(Native Method)
08-06 18:32:56.155: E/AndroidRuntime(4906): at java.lang.reflect.Method.invoke(Method.java:511)
08-06 18:32:56.155: E/AndroidRuntime(4906): at android.view.View$1.onClick(View.java:3594)
08-06 18:32:56.155: E/AndroidRuntime(4906): ... 11 more
08-06 18:32:56.155: E/AndroidRuntime(4906): Caused by: java.lang.NullPointerException
08-06 18:32:56.155: E/AndroidRuntime(4906): at com.evorlor.threecardpoker.SortCards.compare(SortCards.java:10)
08-06 18:32:56.155: E/AndroidRuntime(4906): at com.evorlor.threecardpoker.SortCards.compare(SortCards.java:1)
08-06 18:32:56.155: E/AndroidRuntime(4906): at java.util.TimSort.countRunAndMakeAscending(TimSort.java:320)
08-06 18:32:56.155: E/AndroidRuntime(4906): at java.util.TimSort.sort(TimSort.java:185)
08-06 18:32:56.155: E/AndroidRuntime(4906): at java.util.TimSort.sort(TimSort.java:169)
08-06 18:32:56.155: E/AndroidRuntime(4906): at java.util.Arrays.sort(Arrays.java:2038)
08-06 18:32:56.155: E/AndroidRuntime(4906): at java.util.Collections.sort(Collections.java:1891)





package com.evorlor.threecardpoker;

public class Card {
private int rank;
private char suit;

public Card(int rank, char suit) {
super();
this.rank = rank;
this.suit = suit;
}

public int getRank() {
return rank;
}

public char getSuit() {
return suit;
}

}

Answer Source

One way you can keep this from happening in the future, is to do a null check. When coding, you want to be sure you handle situations like this. One way might look like:

public int getHand(Card c1, Card c2, Card c3) {

    if((c1 != null) && (c2 != null) && (c3 != null)){
        ArrayList<Card> hand = new ArrayList<Card>();
        hand.add(c1);
        hand.add(c2);
        hand.add(c3);

        Collections.sort(hand, new SortCards());
    }else{
        #handle your null card situation here
        System.out.println("One or more card is null");
    }
}
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