RFR: JDK-8344907 : NullPointerException in Win32ShellFolder2.getSystemIcon when "icon" is null

[Alexey Ivanov]

On Mon, 16 Dec 2024 23:49:58 GMT, Harshitha Onkar <honkar at openjdk.org> wrote:

> Win32ShellFolder2.getSystemIcon() can result in NPE if icon is null. Sanity null checks have been added.
> 
> 
> long hIcon = getSystemIcon(iconType.getIconID()); //Can return null
> Image icon = makeIcon(hIcon); // returns null if the condition (hIcon != 0L && hIcon != -1L) is false
> if (LARGE_ICON_SIZE != icon.getWidth(null)) { // NullPointerException -- icon is null
> 
> 
> Occurs when Windows is unable to provide a system icon and the code assumes an icon will **always** be returned, but the Windows API makes no such guarantee.
> 
> getSystemIcon calls LoadIcon (User32.dll). This can return null.
> https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-loadicona

I wonder in what state the problem occurs… [JDK-8344907](https://bugs.openjdk.org/browse/JDK-8344907) states the problem occurs *often*.

I've never seen [`LoadIcon`](https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-loadiconw) fails for the standard icons. The only reason I can think of is when GDI handles are exhausted.

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Changes requested by aivanov (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/22776#pullrequestreview-2509014924