How to get list of all window handles in Java (Using JNA)?

The latest version of JNA has had some changes that should fix this (as one of the authors of JNA, Luke Quinane, states here). If you use the latest version and check the JNA API, you’ll see that the WinUser.WNDENUMPROC interface’s method actually uses WinDef.HWND as its parameter, not long or int.

For example:

import com.sun.jna.Native;
import com.sun.jna.Pointer;
import com.sun.jna.platform.win32.WinDef.HWND;
import com.sun.jna.platform.win32.WinUser;
import com.sun.jna.platform.win32.WinUser.WNDENUMPROC;
import com.sun.jna.win32.StdCallLibrary;

public class TryWithHWND {
   public interface User32 extends StdCallLibrary {
      User32 INSTANCE = (User32) Native.loadLibrary("user32", User32.class);
      boolean EnumWindows(WinUser.WNDENUMPROC lpEnumFunc, Pointer arg);
      int GetWindowTextA(HWND hWnd, byte[] lpString, int nMaxCount);
   }

   public static void main(String[] args) {
      final User32 user32 = User32.INSTANCE;
      user32.EnumWindows(new WNDENUMPROC() {
         int count = 0;
         @Override
         public boolean callback(HWND hWnd, Pointer arg1) {
            byte[] windowText = new byte[512];
            user32.GetWindowTextA(hWnd, windowText, 512);
            String wText = Native.toString(windowText);

            // get rid of this if block if you want all windows regardless of whether
            // or not they have text
            if (wText.isEmpty()) {
               return true;
            }

            System.out.println("Found window with text " + hWnd + ", total " + ++count
                  + " Text: " + wText);
            return true;
         }
      }, null);
   }
}