New to Java

This is my main.java:

import javax.swing.UnsupportedLookAndFeelException;


public class Main
{
   public static void main(String[] args) 
         throws ClassNotFoundException, InstantiationException, IllegalAccessException, UnsupportedLookAndFeelException
   {
      Core window = new Core("GAME1", 0, 0, true, true);
   }
}

And this is my Core.java:

import java.awt.GraphicsEnvironment;
import java.awt.Window;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;


import javax.swing.JFrame;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.WindowConstants;


public class Core extends JFrame implements ActionListener
{
   private final String Game_Title;
   private int Window_Width;
   private int Window_Height;
   private boolean isVisible;
   private boolean isResizeable;
   
   public Core(String Game_Title, int Window_Width, int Window_Height, 
         boolean isVisible, boolean isResizeable) throws ClassNotFoundException, 
         InstantiationException, IllegalAccessException, UnsupportedLookAndFeelException
   {  
      this.Game_Title = Game_Title;
      this.Window_Width = Window_Height;
      this.Window_Height = Window_Height;
      this.isResizeable = isResizeable;
      this.isVisible = isVisible;
      
      //Create JFrame
      JFrame window = new JFrame(Game_Title);
      window.setSize(Window_Width, Window_Height);
      window.setResizable(isResizeable);
      window.setExtendedState(JFrame.MAXIMIZED_BOTH);
      window.setVisible(isVisible);
      window.setDefaultCloseOperation(WindowConstants.DISPOSE_ON_CLOSE);
      window.addKeyListener(new Key_Listener()); // Adding the Key_Listener to the window


      GraphicsEnvironment.getLocalGraphicsEnvironment().getDefaultScreenDevice().setFullScreenWindow(window); // make the window full screen
   }
   @Override
   public void actionPerformed(ActionEvent e)
   {
      //For Buttons and other interface stuff
   }
   
   // KEY LISTENER:
   public class Key_Listener implements KeyListener
   {
      // 112 - F1
      // 113 - F2
      // 114 - F3
      // 115 - F4
      // 27 - ESC
      private char character;
      private int KeyPressed;


      @Override
      public void keyTyped(KeyEvent e)
      {
         
      }


      @Override
      public void keyPressed(KeyEvent e)
      {
         this.character = e.getKeyChar();
         this.KeyPressed = e.getKeyCode();
         System.out.println(character + "::" + KeyPressed);
         if(this.KeyPressed == 112)
         {
            GraphicsEnvironment.getLocalGraphicsEnvironment().getDefaultScreenDevice().setFullScreenWindow(null);
         }
         else if (this.KeyPressed == 113)
         {
            GraphicsEnvironment.getLocalGraphicsEnvironment().getDefaultScreenDevice().setFullScreenWindow(null);
         }
         else if (this.KeyPressed == 114)
         {
            System.out.println("F3");
         }
      }
      public int returnPressedKey()
      {
         return this.KeyPressed;
      }


      @Override
      public void keyReleased(KeyEvent e)
      {
         
      }     
   }
}

In Core.Java at line 80 how can I access window (

JFrame window = new JFrame(Game_Title); // <- this window

) ?

Also should I use throws or try and catch ?