question about next() in arraylist iterator JAVA

Question

I am just wondering what does the highlighted part of the code do here?

public E next() {
        checkForComodification();
        int i = cursor;
        if (i >= size)
        throw new NoSuchElementException();
    Object[] elementData = ArrayList.this.elementData;
    if (i >= elementData.length)
        throw new ConcurrentModificationException();
    cursor = i + 1;
    return (E) elementData[lastRet = i]; // what exactly does lastRet = i do??
}

does lastRet = i assigns i to lastRet? if so, if i = 3, then we have elementData[lastRet = 3]? but what does that do? I understand if I have elementData[0] then I am retrieving elementData at the 0 position, and if I have elementData[2] then I am retrieving elementData at the 3rd position. But what is elementData[lastRet = i]? is lastRet = i actually checking if lastRet equals to i? like lastRet == i? but if so, why not write lastRet ==i instead? so it shouldn't be checking equality. So what does lastRet = i do? so it assigns i to lastRet? But then I don't understand what the code: elementData[lastRet = i] do exactly?

Adding ** to the code is confusing because it's no longer valid. It would be more clear if you removed the ** and just left the comment in the code. — Dave S
– Dave S, Commented Dec 7, 2021 at 3:08

Dave S · Accepted Answer · 2021-12-07 03:03:05Z

1

The value of an assignment statement is the value being assigned.

In this case the value is just i but the statement also has the effect of storing that value in lastRet.

answered Dec 7, 2021 at 3:03

Dave S

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3 Comments

john_w Over a year ago

so it has two operations in there? one is first assigning i to lastRet? and then take the operation of elementData[i] for whatever the value of i is? is it correct?

Dave S Over a year ago

Yes. lastRet is assigned the value of i. The value of that expression is i which is used as the index to the array elementData. It is equivalent to lastRet = i; elementData[i]. Personally, I don't like the syntax elementData[ lastRet = i ]. I would prefer the long version because it is explicit and straightforward. Someone reading your code may have to stop and think for a moment about what elementData[ lastRet = i ] is actually doing. It's a speed bump to readability. Simple and straightforward is better. Use 2 lines to do this.

john_w Over a year ago

thank you for the explanations

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