“Exception in thread ”main“ java.lang.IndexOutOfBoundsException: Index: 0, Size: 0” with ArrayList?

问题

"Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 0, Size: 0" is the main error I get when I compile this method:

public static ArrayList<ArrayList<Integer>> createSparseArray(int len, double den) {
    int counter = 0;
    ArrayList<Integer> placeHolder = new ArrayList<Integer>();
    for (int j = 0; j < len; j++) {
        double randomNumber = Math.random();
        if (randomNumber < den) {
            counter++;
            placeHolder.add(j);
        }
    }
    ArrayList<ArrayList<Integer>> list = new ArrayList<ArrayList<Integer>>();
    for (int k = 0; k < counter; k++) {
        for (int m = 0; m < 2; m++) {
            list.get(0).set(placeHolder.get(k), (int) (Math.random() * (99999) + 1));
        }
    }
    return list;
}

How can I fix this?

回答1:

ArrayList<ArrayList<Integer>> list doesnt contain any element in (0)th postion and the compiler throws out of bounds exception on iterating when it doesn't find any element in the specified postion.

when you try executing list.get(0).set(placeHolder.get(k), (int) (Math.random() * (99999) + 1)); statement , your list doesnt contain any element inside it. you need to iterate the inner list to set the values for the list.

回答2:

Do not use list.set(index, element) on a nonexistent element, since it replaces the old (nonexistent) element with a new one and returns the old one. Instead, use list.add(index, element) and it will work.

回答3:

I thingk u have mistake here

list.get(0).set(placeHolder.get(k), (int) (Math.random() * (99999) + 1));

The java.util.ArrayList.get(int index) method returns the element at the specified position in this list.

You are setting just to first element in the list arrray

来源：https://stackoverflow.com/questions/26272508/exception-in-thread-main-java-lang-indexoutofboundsexception-index-0-size

标签

java

arraylist