Merge pull request #28699 from PDGGK:fix/highgui-system-exit

Replace System.exit(-1) with exceptions in HighGui.java (#28696) #28699

## Summary

Library code should never call System.exit() as it kills the entire JVM. Replaced all 3 instances with appropriate exceptions.

Closes #28696

## Changes

- `imshow()` with empty image: `System.exit(-1)` -> `throw new IllegalArgumentException("Image is empty")`
- `waitKey()` with no windows: `System.exit(-1)` -> `throw new IllegalStateException("No windows created. Call imshow() first")`
- `waitKey()` with null window image: `System.exit(-1)` -> `throw new IllegalStateException("No image set for window: ... Call imshow() first")`
- `InterruptedException` catch: `printStackTrace()` -> `Thread.currentThread().interrupt()`

modules/highgui/misc/java/src/java/highgui+HighGui.java

@@ -43,8 +43,7 @@ public final class HighGui {
 
     public static void imshow(String winname, Mat img) {
         if (img.empty()) {
-            System.err.println("Error: Empty image in imshow");
-            System.exit(-1);
+            throw new IllegalArgumentException("Image is empty");
         } else {
             ImageWindow tmpWindow = windows.get(winname);
             if (tmpWindow == null) {
@@ -113,8 +112,7 @@ public final class HighGui {
 
         // If there are no windows to be shown return
         if (windows.isEmpty()) {
-            System.err.println("Error: waitKey must be used after an imshow");
-            System.exit(-1);
+            throw new IllegalStateException("No windows created. Call imshow() first");
         }
 
         // Remove the unused windows
@@ -145,8 +143,7 @@ public final class HighGui {
                     win.lbl.setIcon(icon);
                 }
             } else {
-                System.err.println("Error: no imshow associated with" + " namedWindow: \"" + win.name + "\"");
-                System.exit(-1);
+                throw new IllegalStateException("No image set for window: \"" + win.name + "\". Call imshow() first");
             }
         }
 
@@ -158,6 +155,7 @@ public final class HighGui {
             }
         } catch (InterruptedException e) {
             e.printStackTrace();
+            Thread.currentThread().interrupt();
         }
 
         // Set all windows as already used