Java Array 索引越界異常修復

Question

我目前在執行行name.firstName = this.firstNames[rand.nextInt(NUM_NAMES)];時得到一個數組越界異常name.firstName = this.firstNames[rand.nextInt(NUM_NAMES)]; 通常我在查找這些異常的來源時沒有問題，但是我已經堅持這個問題有一段時間了。 任何幫助表示贊賞，類和堆棧跟蹤粘貼如下：

public class NameGenerator {
    private static final int NUM_NAMES = 200;
    private static final File NAMES_FILE = new File("resources/info.dat");

    /** a random number generator */
    private Random rand;

    /** the array of first names */
    private String[] firstNames;
    /** the array of last names */
    private String[] lastNames;

    /**
     * Default Constructor
     */
    public NameGen() {
        super();
        this.rand = new Random();

        try {
            readFile();
        } catch (IOException exp) {
            this.first = new String[] { "foo" };
            this.last = new String[] { "bar" };
        }
    }

    /**
     * Read the names from the file
     */
    private void readNFiles() throws IOException {
        List<String> tempFirst = new ArrayList<String>();
        List<String> tempLast = new ArrayList<String>();

        Scanner scnr = new Scanner(NAMES_FILE);

        while (scnr.hasNext()) {
            tempFirst.add(scnr.next());
            tempLast.add(scnr.next());
        }

        scnr.close();

        int size = tempFirst.size();

        this.first = new String[size];
        tempFirst.toArray(this.firstNames);

        this.last = new String[size];
        tempLast.toArray(this.last);
    }

    /**
     * @return a generated name
     */
    public FullName generateName() {
        FullName name = new FullName();
        name.first = this.firstNames[rand.nextInt()];

        name.last = this.lastNames[rand.nextInt()];
        return name;
    }

    /**
     * Class describing a full name
     */
    public static final class FullName {
        /** the first name */
        public String firstName;
        /** the last name */
        public String lastName;
    }
}

Answer 1

基於...

try {

    readNamesFiles();

} catch (IOException exp) {

    this.firstNames = new String[] { "John" };
    this.lastNames = new String[] { "Doe" };

}

不能保證您的數組將包含NUM_NAMES元素（您至少應該記錄異常）。

所以使用類似name.firstName = this.firstNames[rand.nextInt(NUM_NAMES)]; 正如你所發現的，有可能導致一些嚴重的問題。

相反，你應該處理現實而不是假設，使用更像......

name.firstName = this.firstNames[rand.nextInt(this.firstNames.length)];

Answer 2

以下是您有問題的代碼的摘要：

List<String> tempFirstNames = new ArrayList<String>(NUM_NAMES);
int size = tempFirstNames.size();

this.firstNames = new String[size];
FullName name = new FullName();
name.firstName = this.firstNames[rand.nextInt(NUM_NAMES)];

您正在使用rand.nextInt(NUM_NAMES)作為firstNames的數組索引。 這將生成一個介於 0 和NUM_NAMES之間的數字。 問題是不能保證數組firstNames的大小為NUM_NAMES 。 正如@AngryProgrammer 指出的那樣，您可以改用它：

name.firstName = this.firstNames[rand.nextInt(firstNames.length)];