JNA beep() cannot find symbol?

Question

In the code below I get an error, and somehow I couldn't find information to fix it. Sorry for any misunderstandings.

import com.sun.jna.Library;
import com.sun.jna.Native; 
import com.sun.jna.platform.win32.Kernel32;
// JNA infrastructure import libs.Kernel32; 
// Proxy interface for kernel32.dll 

public interface JnaTests extends Library {
  public boolean Beep(int FREQUENCY , int DURATION );
  static Kernel32 kernel32 = (Kernel32) Native.loadLibrary("kernel32",   Kernel32.class); 
  static void toMorseCode(String letter) throws Exception { 
  for (byte b : letter.getBytes()) { 
   kernel32.Beep(1200, ((b == '.') ? 50 : 150)); 
   Thread.sleep(50); 
  } 
 } 
 public static void main(String[] args) throws Exception { 
   String helloWorld[][] = { {"....", ".", ".-..", ".-..", "---"}, {".--", "---", ".-.", ".-..", "-.."}}; 
   for (String word[] : helloWorld) { 
    for (String letter : word) { 
     toMorseCode(letter); 
     Thread.sleep(150); 
    } 
    Thread.sleep(350); 
   }
  } 
 }

Answer 1

Thanks for the answers.

Finally I found that there should be an Interface (Kernel32) in a separated file.

This was mentioned in the community documentation, however some .dll worked also without Interface e.g. User32.dll .

package com.sun.jna.platform;

import com.sun.jna.Library;


//@author windows-System

public class win32 {

 public interface Kernel32 extends Library {

 boolean Beep(int frequency, int duration); 
 // ... (lines deleted for clarity) ... }   
}

}

Main-file

import com.sun.jna.Library;
import com.sun.jna.Native; 
import com.sun.jna.platform.win32.Kernel32;

// JNA infrastructure import libs.Kernel32; 
// Proxy interface for kernel32.dll 

public class JnaTests {

private static Kernel32 kernel32 = (Kernel32)                    
Native.loadLibrary ("kernel32",   Kernel32.class);

private static void toMorseCode(String letter) throws Exception { 
 for (byte b : letter.getBytes()) { 
  kernel32.Beep(1200, ((b == '.') ? 50 : 150)); 
  Thread.sleep(50); 
 }  
} 

public static void main(String[] args) throws Exception { 
 String helloWorld[][] = { {"....", ".", ".-..", ".-..", "---"}, 
 {".--",  "---", ".-.", ".-..", "-.."}}; 

for (String word[] : helloWorld) { 
 for (String letter : word) { 
  toMorseCode(letter); 
  Thread.sleep(150); 
 } 
 Thread.sleep(350); 
}

} }