计算机课实验中ArrayList触发java.lang.IndexOutOfBoundsException的解决求助

Got it, let's break down why you're hitting this exception and fix your code to meet the lab requirements step by step.

Why the IndexOutOfBoundsException occurs #

When you first call addCard (with the Card(4)), your myHand ArrayList is empty (size = 0). Your while loop uses the condition i <= myHand.size()—so 0 <= 0 evaluates to true. Then you call getCardValue(i), which tries to run myHand.get(0)—but since the list has no elements yet, index 0 doesn't exist, hence the exception.

Other logic flaws in your addCard method #

Beyond the exception, your code doesn't align with the lab rules and has extra bugs:

• Incorrect loop condition: Using i <= myHand.size() will always trigger an out-of-bounds error when i equals the list size (since list indices range from 0 to size-1).
• Misaligned insertion logic: The lab asks to find the first Card with a pip value strictly less than c's value, then insert c at that index. Your check c.getValue() >= getCardValue(i) doesn't match this requirement, and you don't break the loop after inserting—this would cause infinite loops or duplicate card inserts.
• No empty list handling: You need to account for adding the first card without entering the loop.

Fixed Code #

Updated getCardValue (with safety check) #

While your original getCardValue works for valid indices, adding a check prevents accidental out-of-bounds errors from invalid input:

public int getCardValue(int n) {
    if (n < 0 || n >= myHand.size()) {
        throw new IllegalArgumentException("Index " + n + " is out of bounds. Hand size is " + myHand.size());
    }
    return myHand.get(n).getValue();
}

Corrected addCard method #

This version follows the lab requirements exactly and fixes the exception:

public void addCard(Card c) {
    int i = 0;
    // Find the first index where the existing card's value is strictly less than c's value
    while (i < myHand.size()) {
        if (myHand.get(i).getValue() < c.getValue()) {
            break; // Exit loop once we find the insertion point
        }
        i++;
    }
    // Insert the new card at the found index (or end if all existing cards are larger)
    myHand.add(i, c);
}

How this works with your test case #

Let's walk through your test scenario to confirm it matches the expected output:

1. Adding Card(4): myHand is empty, loop doesn't run—card is added at index 0 → [4]
2. Adding Card(10): Loop checks index 0 (4 < 10), breaks, inserts at 0 → [10,4]
3. Adding Card(12): Loop checks index 0 (10 <12), breaks, inserts at 0 → [12,10,4]
4. Adding Card(14): Loop checks index 0 (12 <14), breaks, inserts at 0 → [14,12,10,4]
5. Adding Card(2): Loop runs through all elements (14,12,10,4 are all ≥2), i reaches 4 (equal to list size), inserts at end → [14,12,10,4,2]

When you call h.getCardValue(3), it returns the value at index 3 (4), which matches your expected output.

内容的提问来源于stack exchange，提问作者Marcellus McDuff