"Always on TOP"option for my window

Question

Hi All
I am developing an application in which I wanted to develop a facility for enabling "always stay on top" to one of the windows .How can I do this.
Thanks in advance
Haritha

Answer 1

I solved this problem using JNI, and I think that is the only way to allow the "Alwasy on Top" option. Here's how I did it.
1. Create an extension of JFrame or JDialog or JWindow, whatever you want.
2. Add the native method setAlwaysOnTop()
import java.awt.*;
import javax.swing.*;
public class MyFrame extends JFrame {
static { System.loadLibrary("MyFrame"); }
public MyFrame() {
super();
public void setAlwaysOnTop(boolean b) {
int hwnd = getNativeWindowHandle(this);
seteAlwaysOnTop(hwnd, b);
private native int getNativeWindowHandle(Window window);
private native void setAlwaysOnTop(int hwnd, boolean flag);
*NOTE the getNativeWindowHandle method is required to manipulate the frame in native code
**NOTE I will take about the static { System.loadLibrary("MyFrame"); }
at the end.
3. Compile your code.
4. Next you must create a c or c++ source file, name it whate every you want, and then define the setAlwaysOnTop method.
Heres the code for the native file.
#include <jni.h>
#include <jawt.h>
#include <afxwin.h>
#include <windows.h>
#include "MyFrame.h"
#include "jawt_md.h"
JNIEXPORT jint JNICALL
Java_MyFrame_getNativeWindowHandle(JNIEnv *env, jobject jobj, jobject window)
JAWT awt;
awt.version = JAWT_VERSION_1_3;
jboolean result = JAWT_GetAWT(env, &awt);
if (result == JNI_FALSE)
return 0;
JAWT_DrawingSurface* ds = awt.GetDrawingSurface(env, window);
if (ds == 0)
return 0;
jint lock = ds->Lock(ds);
if ((lock & JAWT_LOCK_ERROR) != 0)
return 0;
JAWT_DrawingSurfaceInfo* dsi = ds->GetDrawingSurfaceInfo(ds);
if (dsi != 0)
return 0;
JAWT_Win32DrawingSurfaceInfo* dsiwin = (JAWT_Win32DrawingSurfaceInfo*) dsi->platformInfo;
jint ret = reinterpret_cast<jint>(dsiwin->hwnd);
ds->FreeDrawingSurfaceInfo(dsi);
ds->Unlock(ds);
awt.FreeDrawingSurface(ds);
return ret;
JNIEXPORT void JNICALL
Java_MyFrame_windowAlwaysOnTop(JNIEnv *env, jobject jobj, jint hwnd, jboolean flag)
if (flag)
SetWindowPos((HWND) hwnd,HWND_TOPMOST,0,0,0,0,SWP_NOMOVE|SWP_NOSIZE);
else
SetWindowPos((HWND) hwnd,HWND_NOTOPMOST,0,0,0,0,SWP_NOMOVE|SWP_NOSIZE);
*NOTE say your class MyFrame is in the package com.me.swing then the method prototype would look like this:
JNIEXPORT void JNICALL
Java_com_me_swing_MyFrame_windowAlwaysOnTop(JNIEnv *env, jobject jobj, jint hwnd, jboolean flag)
5. you may have noticed the #include "MyFrame.h" line, well that is generated by the javah command. So, next run javah on your MyFrame.class file. you will have to look at the options to configure the command to do what you want, but essentially "javah MyFrame.class".
6. Make sure your MyFrame.h file and MyFrame.c or MyFrame.cpp file is in the same directory and compile them into an object file. Now you will have to figure out how to do this on your own. First you must get a c++ compiler, I use Visual C++ form Microsoft. If you are using that then
here is the command line
cl -Ic:\j2sdk1.4.0\include -Ic:\j2sdk1.4.0\include\win32 /c -LD
-IMyFrame.h MyFrame.cpp
Execute this command from the directory where you MyFrame.h and MyFrame.cpp files are or you will have to specify their paths.
the -Ic:\j2sdk1.4.0\include -Ic:\j2sdk1.4.0\include\win32 provide path information to include the jni.h and jawt.h files.
7. Now you will have to link the object file with the jawt.lib file and create the final dll. Again you will have to figure how to do this, but with VC++ the command is.
link /DLL MyFrame.obj c:\j2sdk1.4.0\lib\jawt.lib
Now you should 8 have files
MyFrame.java
MyFrame.class
MyFrame.h *created form javah
MyFrame.cpp
MyFrame.obj *created from compiling
MyFrame.exp *created from compiling
MyFrame.lib *created from compiling
MyFrame.dll *created from linking
You are done, now create a main class and instanciate and test your new frame.
**REMEBER the static { System.loadLibrary("MyFrame"); } line in your MyFrame.java file. This loads your newly created dll into the system so you can access it.
**IMPORTANT THE MyFrame.dll AND THE MyFrame.class FILE MUST BE IN THE SAME DIRECTORY, OR SPECIFY IT IN THE System.loadLibrary METHOD CALL.