不确定为什么我在这个循环中得到Null异常

Question

I've got a constructor for a class that iterates over a ArrayList of ImageIcon s, but half way through it crashes with a NullPointerException. Any ideas why?

for (ImageIcon i : dm.GetIcons())
{
    _labels.add(new JLabel(i));
}

public ArrayList<ImageIcon> GetIcons(){
    return _icons;  
}

I tried throwing GetIcons into a variable and set a breakpoint, it has 8 items (exactly as I expect) but by the time I Step Over my loop 2 or 3 times it crashes. No idea what I'm doing wrong. Newbie to Java. Any thoughts?

Answer 1

You have null element/s in the List of ImageIcon s

You can check for nullity first,

for (ImageIcon i : dm.GetIcons())
{
    if (i != null) {
        _labels.add(new JLabel(i));
    }
}

Only if it is ok to skip null elements ie depending on what your app needs.

Answer 2

您的ImageIcon ArrayList可能包含一些空对象或没有值的Empty对象