CODEWITHSUNDEEP
javagenericspolymorphism
helsont
helsont

Reputation: 4952

Instantiating Generic Object

I have a method that accepts a subtype of Button2. This method does some calculations and creates buttons to be place in an ArrayList so that they are arranged in a graphical way. Here's my code:

public void createButtonArray(ArrayList<? extends Button2> buttonList,
        int xLength, int yLength, int width, int height, int inset) {

    // The total size for the inset, or spaces between buttons
    int totalInset = (xLength - 1) * inset;
    // The total height = height of buttons + size of insets
    int totalHeight = totalInset + 5 * height;
    // ... More calculations

The it comes to this. I don't know how to say this following line because the compiler gives me syntactical errors. How do I create a button that's a subtype of Button2? 

Button2<?> button = new Button2(xpos, ypos, width, height);
buttonList.add(button);
counter++;

I've also tried this:

buttonList.add(new <? extends Button2>(xpos,ypos,width,height));

which also gives me an error. How can I create this button to add to my generic ArrayList?

Upvotes: 0

Views: 130

Answers (1)

tcb
tcb

Reputation: 2824

You cannot add any objects (except null) into ArrayList<? extends Button2>, but you can pass just ArrayList<Button2> to your function and then do buttonList.add(new Button2(xpos,ypos,width,height)).

Upvotes: 1

Related Questions