安卓 IllegalArgumentException

Question

运行以下方法时，我不断收到 IllegalArgumentException:

public int randomize(ArrayList<Integer> list){
    Random rdm = new Random();  
    int size = list.size(); 
    int chosen = rdm.nextInt(size);
    Integer card = list.get(chosen);
    list.remove(chosen);
    return card;
}  

这是 StackTrace:

11-22 16:52:16.890: E/AndroidRuntime(24979): FATAL EXCEPTION: main
11-22 16:52:16.890: E/AndroidRuntime(24979): java.lang.RuntimeException: Unable to start activity ComponentInfo{edu.marshall.meadows182.match/edu.marshall.meadows182.match.Match}: java.lang.IllegalArgumentException
11-22 16:52:16.890: E/AndroidRuntime(24979):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1821)
11-22 16:52:16.890: E/AndroidRuntime(24979):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1842)
11-22 16:52:16.890: E/AndroidRuntime(24979):    at android.app.ActivityThread.access$1500(ActivityThread.java:132)
11-22 16:52:16.890: E/AndroidRuntime(24979):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1038)
11-22 16:52:16.890: E/AndroidRuntime(24979):    at android.os.Handler.dispatchMessage(Handler.java:99)
11-22 16:52:16.890: E/AndroidRuntime(24979):    at android.os.Looper.loop(Looper.java:143)
11-22 16:52:16.890: E/AndroidRuntime(24979):    at android.app.ActivityThread.main(ActivityThread.java:4263)
11-22 16:52:16.890: E/AndroidRuntime(24979):    at java.lang.reflect.Method.invokeNative(Native Method)
11-22 16:52:16.890: E/AndroidRuntime(24979):    at java.lang.reflect.Method.invoke(Method.java:507)
11-22 16:52:16.890: E/AndroidRuntime(24979):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
11-22 16:52:16.890: E/AndroidRuntime(24979):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
11-22 16:52:16.890: E/AndroidRuntime(24979):    at dalvik.system.NativeStart.main(Native Method)
11-22 16:52:16.890: E/AndroidRuntime(24979): Caused by: java.lang.IllegalArgumentException
11-22 16:52:16.890: E/AndroidRuntime(24979):    at java.util.Random.nextInt(Random.java:186)
11-22 16:52:16.890: E/AndroidRuntime(24979):    at edu.marshall.meadows182.match.Match.randomize(Match.java:200)
11-22 16:52:16.890: E/AndroidRuntime(24979):    at edu.marshall.meadows182.match.Match.initArrays(Match.java:108)
11-22 16:52:16.890: E/AndroidRuntime(24979):    at edu.marshall.meadows182.match.Match.onCreate(Match.java:218)
11-22 16:52:16.890: E/AndroidRuntime(24979):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1072)
11-22 16:52:16.890: E/AndroidRuntime(24979):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1785)
11-22 16:52:16.890: E/AndroidRuntime(24979):    ... 11 more

我正在传递的 ArrayLists 中确实有元素(或者它们通过应该将它们放在那里的方法传递)有人知道这是为什么吗？

Answer 1

来自 javadoc:

public int nextInt(int n)

Throws:

   IllegalArgumentException - n is not positive.

编辑:我尝试使用这段代码:

public static void main(String args[]) {
    Random r = new Random();

    System.out.println(r.nextInt(0)); // <-- error
    // It cannot return a value between 0 (inclusive) and... 0 (exclusive!!!)
}

输出是一个 IllegalArgumentExcepion:

Exception in thread "main" java.lang.IllegalArgumentException: n must be positive
    at java.util.Random.nextInt(Unknown Source)
    at Random0.main(Random0.java:7)

如果您的列表为空，您的变量大小可能为 0，这不是正值。您必须捕获这种特殊情况并加以管理。