Type mismatch: cannot convert from void to ArrayList

Question

Why am I getting this error for this code? I have the correct imports for ArrayList an Collections

private ArrayList tips;

public TipsTask(ArrayLi         


        

Answer 1

You should call it like this:

private ArrayList<String> tips;

public TipsTask(ArrayList<String> tips){
    this.tips = tips;
    Collections.shuffle(tips);
}

Collections.shuffle(tips) modifies the ArrayList directly. It does not need to create a copy.

Answer 2

The problem is that Collections.shuffle method doesn't return anything.

You can try this:

private ArrayList<String> tips;

public TipsTask(ArrayList<String> tips){
    this.tips = new ArrayList<String>(tips);
    Collections.shuffle(this.tips);
}

Answer 3

Collections.shuffle(tips) returns void. So you cannot assign this to an ArrayList()

What you want is

private ArrayList<String> tips;

public TipsTask(ArrayList<String> _tips){
    Collections.shuffle(_tips);
    this.tips = _tips;
}

Answer 4

Collections.shuffle(tips);

Collections.shuffle return void, you cannot assign void to a ArrayList.

you could do for example:

    Collections.shuffle(tips);
    this.tips = tips;

Answer 5

I think you should write it like this:

private List<String> tips;

public TipsTask(List<String> tips) {
    this.tips = new ArrayList<String>(tips);
    Collections.shuffle(this.tips);
}

The other way breaks making the List private. The person with the original reference can manipulate your private state.

Answer 6

Collections.shuffle shuffles the array in-place. This will be sufficient:

private ArrayList<String> tips;

public TipsTask(ArrayList<String> tips){
    this.tips = tips;
    Collections.shuffle(tips);
}

Or if you don't want the original list to change:

private ArrayList<String> tips;

public TipsTask(ArrayList<String> tips){
    this.tips = new ArrayList<String>(tips);
    Collections.shuffle(this.tips);
}