Question

I have two Java swing applications (means running in two JVM). Is there any way to switch between them? Active another application’s window by Java code?

Answer 1

You can try using JNA. I’ll give you some code for Windows (more or less will be for other systems) using Maven:
(sorry but I cannot get formatting right)

1. Create Maven project, and add dependencies:

   <dependency>
       <groupId>net.java.dev.jna</groupId>
       <artifactId>jna</artifactId>
       <version>3.4.0</version>
   </dependency>
   <dependency>
       <groupId>net.java.dev.jna</groupId>
       <artifactId>platform</artifactId>
       <version>3.4.0</version>
   </dependency>
   

2. Create interface

   public interface User32 extends StdCallLibrary {
       User32 INSTANCE = (User32) Native.loadLibrary("user32", User32.class, W32APIOptions.DEFAULT_OPTIONS);
       HWND GetParent(HWND hWnd);
       HWND FindWindow(String lpClassName, String lpWindowName);
       HWND SetFocus(HWND hWnd);
       HWND FindWindowEx(HWND hwndParent, HWND hwndChildAfter, String lpszClass, String lpszWindow);
       int GetWindowText(HWND hWnd, char[] lpString, int nMaxCount);
   }
   

3. Create class

   public final class Win32WindowUtils {
       private static final int WIN_TITLE_MAX_SIZE = 512;
   
       public HWND GetWindowHandle(String strSearch, String strClass) {
           char[] lpString = new char[WIN_TITLE_MAX_SIZE];
           String strTitle;
           int iFind = -1;
           HWND hWnd = User32.INSTANCE.FindWindow(strClass, null);
           while(hWnd != null) {
               User32.INSTANCE.GetWindowText(hWnd, lpString, WIN_TITLE_MAX_SIZE);
               strTitle = new String(lpString);
               strTitle = strTitle.toUpperCase();
               iFind = strTitle.indexOf(strSearch);
               if(iFind != -1) {
                   return hWnd;
               }
               hWnd = User32.INSTANCE.FindWindowEx(null, hWnd, strClass, null);
           }
           return hWnd;
       }
   }
   

4. And invoke

   User32.INSTANCE.SetFocus(Win32WindowUtils.GetWindowHandle(windowTitle.toUpperCase(), null);
   

Of course – windowTitle is your window title (String) that you want to focus.