java - 如何修复哈希表中的 ArrayIndexOutOfBoundsException？

Question

我想知道是否有人可以帮助我尝试运行测试器类时发生的 ArrayIndexOutOfBoundsException。

哈希表文件中的删除方法发生异常。我尝试过将我的代码与我 friend 的代码交换，但这也不起作用。

任何帮助将不胜感激

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这是哈希表:

public class HashTable {

Object[] hTable;
int mSize;
int size;

HashTable() {
    mSize = 101;
    hTable = new Object[mSize];
}

HashTable(int initCap) {
    mSize = initCap;
}

Object put(Object key, Object value) {
    if (size == mSize) {
        throw new IllegalStateException("No room within the hashtable");
    }

    int hashC = key.hashCode();
    int index = hashC % mSize;

    size++;

    while (index < hTable.length) {
        if (hTable[index] == null) {
            hTable[index] = new Entry(key, value);
            size++;
            return null;

        } else if (((Entry) hTable[index]).key.equals(key)) {
            Object prevVal = ((Entry) hTable[index]).val;
            hTable[index] = new Entry(key, value);
            return prevVal;

        } else if (((Entry) hTable[index]).rCheck) {
            hTable[index] = new Entry(key, value);

            while (index < hTable.length) {
                index++;
                if (hTable[index] == null) {
                    size++;
                    return null;
                } else if (((Entry) hTable[index]).key.equals(key)) {

                    Object prevVal = ((Entry) hTable[index]).val;
                    ((Entry) hTable[index]).remove();

                    return prevVal;
                }
            }
        }
        index++;
    }

    if (hTable[index] == null) {
        hTable[index] = new Entry(key, value);
        return null;

    } else {

        Object oldEntry = ((Entry) hTable[index]).val;
        hTable[index] = new Entry(key, value);
        return oldEntry;
    }

}

Object get(Object key) {
    int hashC = key.hashCode();
    int index = hashC % mSize;

    return ((Entry) hTable[index]).val;
}

Object remove(Object key) {
    int hashC = key.hashCode();
    int index = hashC % mSize;

    Object returnObj = null;

    while (hTable[index] != null) { //here is where the OutOfBounds error occurs
        if (((Entry) hTable[index]).key.equals(key)) {
            returnObj = ((Entry) hTable[index]).val;
            ((Entry) hTable[index]).remove();

            size--;
            break;
        }
        index++;
    }
    return returnObj;
}

int size() {
    return size;
}

@Override
public String toString() {
    String returnString = "";

    for (int i = 0; i < hTable.length; i++) {
        if (hTable[i] == null || ((Entry) hTable[i]).rCheck) {
            returnString += "dummy\n";
            continue;
        }

        returnString += "Index: " + i +
                " \n Key: " + ((Integer) (((Entry) hTable[i]).key)).intValue() % 101 +
                "\nValue: " + (String) (((Entry) hTable[i]).val) +
                "\n++++++++++++++++++++++++++++++++++++++++++++++\n";
    }

    return returnString;
}

private class Entry {
    Object key;
    public boolean rCheck;
    public Object val;

    Entry() {
        key = null;
        val = null;
        rCheck = false;
    }

    Entry(Object k, Object v) {
        key = k;
        val = v;
        rCheck = false;
    }

    Object value() {
        return val;
    }

    Object key() {
        return key;
    }

    void remove() {
        rCheck = true;
    }

    public String toString() {
        return "";
    }
}
}

这是哈希表测试器:

    import java.io.*;
    import java.util.*;

public class hashTest {
    public static void main(String args[]) throws FileNotFoundException {
        HashTable hashTable = new HashTable();
        Scanner fileRead = new Scanner(new File("data1.txt"));
        while(fileRead.hasNext()) {
            Object key = fileRead.next();
            fileRead.next();
            Object value = fileRead.nextLine();
            hashTable.put(key, value);
            System.out.println(hashTable.get(key));
        }
        Scanner fileRead2 = new Scanner(new File("data2.txt"));
        while(fileRead2.hasNext()){
            Object key = fileRead2.next();
            hashTable.remove(key);
            fileRead2.nextLine();

        }
        Scanner fileRead3 = new Scanner(new File("data3.txt"));
        while(fileRead3.hasNext()){
            Object key = fileRead3.next();
            fileRead3.next();
            Object value = fileRead3.nextLine();
            hashTable.put(key, value);

        }
        Scanner fileRead4 = new Scanner(new File("data4.txt"));
        while(fileRead4.hasNext()){
            Object key = fileRead4.next();
            fileRead4.next();
            Object value = fileRead4.nextLine();
            hashTable.put(key, value);

        }
    }
}

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在下面的共享 Google 云端硬盘链接中，您将找到一个包含数据输入的 zip。

https://drive.google.com/file/d/1iYrzWl9mtv_io3q7K1_m2EtPFUXGbC3p/view?usp=sharing

Answer 1

您的问题出在这个代码块:

 while (index < hTable.length) {
    index++;
    if (hTable[index] == null)...

在最后一次迭代中，index 将与 hTable.length 相同。在您的示例中，条件将被接受，index 将为 100。在下一步中，索引将增加:index = 101。在hTable[101]处，将发生ArrayIndexOutOfBoundsException。