Question

我正在开发Android Studio中的Asteroid道奇游戏。我使用java中的in random生成器为每个小行星创建随机位置。我一直收到java.lang.IllegalArgumentException: n must be positive，但它在我的手机上仍能正常运行。

例外：

java.lang.IllegalArgumentException: n must be positive
    at java.util.Random.nextInt(Random.java:300)
    at ca.alnitakstudios.Asteroids.Asteroids.<init>(Asteroids.java:38)
    at ca.alnitakstudios.Screens.GameScreen.<init>(GameScreen.java:36)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
    at android.view.LayoutInflater.rInflate_Original(LayoutInflater.java:802)
    at android.view.LayoutInflater_Delegate.rInflate(LayoutInflater_Delegate.java:64)
    at android.view.LayoutInflater.rInflate(LayoutInflater.java:778)
    at android.view.LayoutInflater.inflate(LayoutInflater.java:500)
    at android.view.LayoutInflater.inflate(LayoutInflater.java:381)

代码：

public class Asteroids {

private Random random;

private int amountOfAsteroids, fastestSpeed, slowestSpeed,
biggest, smallest;
private int[] x, y, speeds, radii;

public Asteroids() {
    amountOfAsteroids = 5;
    x = new int[amountOfAsteroids];
    y = new int[amountOfAsteroids];

    speeds = new int[amountOfAsteroids];
    radii = new int[amountOfAsteroids];

    fastestSpeed = 7;
    slowestSpeed = 3;

    biggest = 20;
    smallest = 10;

    random = new Random();

    for (int i = 0; i < amountOfAsteroids; i++) {
        //init x & y placement
        x[i] = random.nextInt(GameScreen.width * 2) + GameScreen.width;
        y[i] = random.nextInt(GameScreen.height);

        //Setting speeds
        speeds[i] = random.nextInt(fastestSpeed - slowestSpeed) + slowestSpeed;

        //Setting the radii
        radii[i] = random.nextInt(biggest - smallest) + smallest;
    }
}

public void draw(Canvas canvas) {
    Paint paint = new Paint();
    paint.setStyle(Paint.Style.FILL);
    paint.setColor(Color.GRAY);

    for(int i = 0; i < amountOfAsteroids; i++) {
        x[i] -= speeds[i];
        canvas.drawCircle(x[i], y[i], radii[i], paint);
    }

    checkIfOutOfBounds();
}

public void checkIfOutOfBounds() {
    for(int i = 0; i < amountOfAsteroids; i++) {
        if(x[i] < 0) {
            //x & y placement after its been out of bounds
            x[i] = random.nextInt(GameScreen.width * 2) + GameScreen.width;
            y[i] = random.nextInt(GameScreen.height);

            //Setting new speeds
            speeds[i] = random.nextInt(fastestSpeed - slowestSpeed) + slowestSpeed;
            //Setting new radii
            radii[i] = random.nextInt(biggest - smallest) + smallest;
        }
    }
}

}

Answer 1

n must be positive   at java.util.Random.nextInt

您向nextInt方法传递了一个否定值，确保在扣除fastestSpeed - slowestSpeed和biggest - smallest时它不是负数。或者您也可以使用Math.abs将所有负数都设为正数

<强>样品：

Math.abs(fastestSpeed - slowestSpeed)

Answer 2

查看堆栈跟踪，似乎问题可能是，因为您在初始化{{1}期间尝试使用GameScreen的静态成员}}。这些静态成员是否正确初始化为正值？如果它们被初始化为GameScreen，这将是一个问题。

由于你非常肯定它应该总是正面的，但不知怎的，你仍然得到零或负值，我建议你创建一个虚拟 0类来进行调试。

Random

这应该覆盖package ca.alnitakstudios.Asteroids; public class Random { private java.util.Random r = new java.util.Random(); public int nextInt(int i) { //Debugging (enable if you need to trace) //new Exception().printStackTrace(); //(or you can also:) //StackTraceElement ste = new Exception().getStackTrace()[1]; //the caller //print out ste.getClassName(), ste.getMethodName(), ste.getLineNumber() etc. System.err.println("nextInt called with value " + i); return r.nextInt(i); } }类中使用的Random类，否则您可以明确导入它。不需要更改其他代码，因此您肯定知道您不会无意中修改任何内容。

java.lang.IllegalArgumentException：n必须是正Android Studio

2 个答案: