Arraylist java.lang.IndexOutOfBoundsException：索引 3 超出长度 3 错误的范围

Question

I created a method which takes an Arraylist of string and an integer. It's going to remove all string whose length is less than the given integer.

For example:

Arraylist = ["abcde", "aabb", "aaabbb", "abc", "ab"]

integer = 4

So the new Arraylist should be: ["abcde", "aabb", "aaabbb"]

But I'm getting this error message:

Exception in thread "main" java.lang.IndexOutOfBoundsException: Index 3 out of bounds for length 3

Here is my code:

public static void main(String[] args){
        ArrayList<String> newArrayList = new ArrayList<>();
        newArrayList.add("string1");
        newArrayList.add("string2");
        newArrayList.add("rem");
        newArrayList.add("dontremove");
        removeElement(newArrayList, 4); // new arraylist must be = [string1, string2, dontremove]
    }


    public static void removeElement(ArrayList<String> arraylist, int inputLen){
        int arrayLen = arraylist.size();
        for(int i=0; i<arrayLen; i++){
            if(arraylist.get(i).length() < inputLen){
                arraylist.remove(i);
                i--;
            }
        }
        System.out.println("New Arraylist: " + arraylist);
    }

What's wrong with this code?

Answer 1

You're looping from 0 to the size of the array which is 4. Inside the loop you're removing items so the size of the array becomes less than 4, so you get this exception. Try looping like this:

Iterator<String> iterator = arraylist.iterator();

while (iterator.hasNext()) {
    String word = iterator.next();
    if (word.length() < inputLen) {
        iterator.remove();
    }
}

Answer 2

You're modifying the list while iterating over its indexes. Once you remove the first item, the list will be shorter than you expect, and you'll get this error once you reach the index of the original last element. Luckily, the removeIf method can do the heavy lifting for you:

public static void removeElement(List<String> arraylist, int inputLen) {
    arraylist.removeIf(s -> s.length() < inputLen);
    System.out.println("New Arraylist: " + arraylist);
}

Answer 3

int arrayLen = arraylist.size();

The problem is that your index has a value of 4.

But then as soon as you remove an item from the list you now only have 3 entries.

So in your loop when you try to access the the 4th entry you will now get an IndexOutOfBounds error.

The solution is to start at the end of the ArrayList and count down to 0.

For (int i = arrayLen - 1; i >= 0; i--)

and inside the loop you don't need the:

i--;

Answer 4

The length of the array should change when you remove elements. The arrayLen variable stores the length of the array, but doesn't change when the array's length shrinks. To change it, you should be able to just replace arrayLen with arrayList.size() , which will change when your remove elements