java.lang.IndexOutOfBoundsException: Index: 0, Size: 0 exception [duplicate]

问题

I am getting the error java.lang.IndexOutOfBoundsException: Index: 0, Size: 0.

public Collection<AdDistribution> getAdDistribution(byte srch, byte cont) throws IndexOutOfBoundsException {

    List<AdDistribution> mediums = new ArrayList<>();
    List<AdDistribution> adDistribution = new ArrayList<>();
            adDistribution.add(AdDistribution.SEARCH);
            adDistribution.add(AdDistribution.CONTENT);
            if (adDistribution.isEmpty()) {
                return null;
              }

    if (srch == 0 && cont == 0) {
        mediums = new ArrayList<>();
        mediums.set(0, adDistribution.get(0));
    }
    if (srch == 1 || cont == 1) {
        mediums = new ArrayList<>();
        if (srch == 1) {
            mediums.set(0, adDistribution.get(0));
        } else if (cont == 1) {
            mediums.set(0, adDistribution.get(1));
        }
    }
    if (srch == 1 && cont == 1) {
        mediums = new ArrayList<>();
        mediums.set(0, adDistribution.get(0));
        mediums.set(1, adDistribution.get(1));
    }
            return mediums;
}

回答1:

The problem is that you are using set method to update element at index 0

set(index,value) method needs an element to present at that index

but you haven't added any element at that position in medium arraylist before that .

So you need to first add an element at index 0 thereafter only you can update it with set method

回答2:

You need to use

mediums.add(adDistribution.get(0));

rather than mediums.set(0, adDistribution.get(0)); etc.

ArrayList.set(int, Object) requires there to be an element to replace:

Replaces the element at the specified position in this list with the specified element.

Throws: IndexOutOfBoundsException - if the index is out of range (index < 0 || index >= size())

In a new list, size() == 0, so set(0, something) fails.

回答3:

EDIT: I just removed the unnecessary if statements and simplified them to make your code more readable.
Then I have replaced the set functions with the add function, because the set only can set existing elements.

EDIT2: Based on Andy Turner's answer, I modified my code. Thank you for the suggestions!

After these modifications, the code should look like this (add/remove/modify it for your needs):

public Collection<AdDistribution> getAdDistribution(byte srch, byte cont) throws IndexOutOfBoundsException {

    List<AdDistribution> mediums = new ArrayList<>();

    if( ( srch == 0 && cont == 0 ) || srch == 1 ) {
        mediums.add(AdDistribution.SEARCH);
    }

    if( cont == 1 ) {
        mediums.add(AdDistribution.CONTENT);
    }

    return mediums;
}

来源：https://stackoverflow.com/questions/39077303/java-lang-indexoutofboundsexception-index-0-size-0-exception

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java

indexoutofboundsexception