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Java error with WindowAdapter and WindowDestroyer

I'm just starting out in java and trying to use some example code I found online to get started, but for some reason, I am unable to compile this code. I on Ubuntu 16.04 and I have the "default-jdk" installed.
Here's the code:
import java.awt.*;
import java.awt.event.WindowListener;
import javax.swing.*;
import java.io.*;
public class Test extends JFrame{
public static void main (String argv [])
{
new Test("Window Application");
}
public Test(String title)
{
super(title);
setSize(200, 100);
addWindowListener((WindowListener) new WindowDestroyer());
setVisible(true);
}
private class WindowDestroyer extends WindowAdapter
{
public void windowClosing(WindowEvent e)
{
System.exit(0);
}
}
}
When I try doing javac Test.java I get 2 cannot find symbol errors.
private class WindowDestroyer extends WindowAdapter
public void windowClosing(WindowEvent e)

From the Java 8 docs for WindowAdapter, it is defined as java.awt.event.WindowAdapter.
You need to import the class first:
import java.awt.event.WindowAdapter;
in addition to your other imports.
import java.awt.*;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowListener;
As a side note, you might be tempted to just do
import java.awt.event.*;
to avoid import errors like that in the future.
I suggest reading the discussions on Why is using a wild card with a Java import statement bad? to have an idea on the pro's and con's of doing so.

I can see, that you create simple Swing application window and close it close window. You do it in incorrect way. It is much better to use setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE) (only if you not plan to do smth. special before). And use SwingUtilities.invokeLater() to execute asynchronously on the AWT event dispatching thread:
public class Test extends JFrame {
public static void main(String... ars) {
SwingUtilities.invokeLater(() -> new Test().setVisible(true));
}
public Test() {
super("Window Application");
setSize(200, 100);
setDefaultCloseOperation(EXIT_ON_CLOSE);
}
}

Why is getItemInHand being crossed out (see image below)

I am new to creating minecraft plugins, however not new to programming, I am following a tutorial very thoroughly, the video has good ratings so it is trusted, when watching the video the guy has no problems what so ever (Youtube video on developing minecraft plugins) , so I did some research into solutions but always the line through the code.
Eclipse gives me the option for: #SuppressWarnings("deprecation") which allows the code to be used still but I would rather have no need of that usage.
Basically my question is why is there the need of the line going through the code and how do I find a solution to get rid of it.
Main class:
package com.jc1;
import org.bukkit.Material;
import org.bukkit.command.Command;
import org.bukkit.command.CommandSender;
import org.bukkit.entity.Player;
import org.bukkit.inventory.ItemStack;
import org.bukkit.permissions.Permission;
import org.bukkit.plugin.PluginManager;
import org.bukkit.plugin.java.JavaPlugin;
public class Core extends JavaPlugin
{
public Permission pPermission = new Permission("playerAbilities.allowed");
#Override
public void onEnable()
{
new BlockListener(this);
PluginManager pm = getServer().getPluginManager();
pm.addPermission(pPermission);
}
#Override
public void onDisable()
{
}
public boolean onCommand(CommandSender sender, Command cmd, String label, String[] args)
{
if(cmd.getName().equalsIgnoreCase("giveitems") && sender instanceof Player)
{
Player p = (Player) sender;
if(p.hasPermission("playerAbilities.allowed"))
{
p.setItemInHand(new ItemStack(Material.DIAMOND_BOOTS));
}
return true;
}
return false;
}
}
Secondary class:
package com.jc1;
import org.bukkit.entity.Player;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.block.BlockPlaceEvent;
public class BlockListener implements Listener
{
public BlockListener(Core plugin)
{
plugin.getServer().getPluginManager().registerEvents(this, plugin);
}
#EventHandler
public void onBlockPlace(BlockPlaceEvent e)
{
Player p = e.getPlayer();
if(!p.hasPermission("playerAbilities.allowed"))
{
e.setCancelled(true);
}
}
}

The method is deprecated, meaning that it is not recommended to be used anymore and is most likely replaced with another method.
Methods that are deprecated may still work as intended.
A simple search for the method reveals (this) documentation, stating:
players can duel wield now use the methods for the specific hand instead
which referes to the #see references:
getItemInMainHand() and getItemInOffHand().

Use this:
player.getInventory().getItemInMainHand()
Instead of:
player.getItemInHand()
Hope this helps! :D

How to create/use/import a custom made Method on Java

Like the in-built Math class, there are a couple of methods that one can use without importing the Math class. e.g
int io = (int) Math.random();
and notice the import region: no MATH whatsoever
import java.awt.Color;
import java.awt.Graphics;
import javax.swing.JPanel;
but seeing, Math set doesn't have everything i needed, i created mine in a new class, but i can't seem to figure out what to do so i can be able to use it.
Taking a hint from the Math.java file, I've made my class final and my methods static but no avail..
Here's an excerpt of my code
package customops.Sets;
/**
*
* #author Kbluue
*/
public final class SetOpz {
public SetOpz(){}
public static int setMax(int[] set){
int out = set[0];
for(int i=1; i<set.length; i++){
out = Math.max(out, set[i]);
}
return out;
}
how do i use just the import command without having to copy and paste the SetOpz class in the DTL package?

You don't need to import Math explicitly because it is included by default. To use your own code you will have to import it. If you're using IntelliJ or Eclipse or some other smart IDE it will offer to import it for you automatically. Otherwise add a import statement at the top:
import customops.Sets.SetOpz;

You can import your method wherever you want to use with the following import statement
import static customops.Sets.SetOpz.setMax;

Icon not showing when jar file is run

I'm a beginner in Java and I followed a tutorial to write this program (yes, I that much of a beginner) and it works perfectly when I run it on Eclipse. It also runs great on the computer I coded it on. However, if I send it to another computer (just the .jar file) and run it, it fails because it can't find the icon. Here is everything I've got. The icon I'm using is saved in the bin folder along with all the class files for the program. For privacy reasons, I replaced certain lines with "WORDS".
The tutorial I followed in two parts:
Part 1 - https://buckysroom.org/videos.php?cat=31&video=18027
Part 2 - https://buckysroom.org/videos.php?cat=31&video=18028
My main class (I called it apples cause the tutorial did).
import javax.swing.JFrame;
public class apples {
public static void main(String[] args) {
Gui go = new Gui();
go.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
go.setSize(1920,1080);
go.setVisible(true);
}
}
And now my second class, "Gui":
import java.awt.FlowLayout;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import javax.swing.JFrame;
import javax.swing.JButton;
import javax.swing.Icon;
import javax.swing.ImageIcon;
import javax.swing.JOptionPane;
public class Gui extends JFrame {
private JButton custom;
public Gui () {
super("WORDS");
setLayout(new FlowLayout());
Icon b = new ImageIcon(getClass().getResource("b.png"));
custom = new JButton(null, b);
custom.setToolTipText("WORDS");
add(custom);
HandlerClass handler = new HandlerClass();
custom.addActionListener(handler);
}
private class HandlerClass implements ActionListener {
public void actionPerformed(ActionEvent event) {
JOptionPane.showMessageDialog(null, String.format("WORDS", event.getActionCommand()));
JOptionPane.showMessageDialog(null, String.format("WORDS", event.getActionCommand()));
JOptionPane.showMessageDialog(null, String.format("WORDS", event.getActionCommand()));
JOptionPane.showMessageDialog(null, String.format("WORDS", event.getActionCommand()));
}
}
}
Thank you so much for helping!

It's worth reading Loading Images Using getResource where it's explained in detail along with loading images from jar as well.
You can try any one based on image location.
// Read from same package
ImageIO.read(getClass().getResourceAsStream("b.png"));
// Read from src/images folder
ImageIO.read(getClass().getResource("/images/b.png"))
// Read from src/images folder
ImageIO.read(getClass().getResourceAsStream("/images/b.png"))
Read more...

Set Clipboard Contents

I am trying to figure out why setting the contents of the system clipboard won't work for me. I programmatically set the clipboard contents. When i use the output part of the code, it works. However, when i try copy/pasting in any text editor, it is blank.
hovercraft edit, code from github:
import java.awt.HeadlessException;
import java.awt.Toolkit;
import java.awt.datatransfer.DataFlavor;
import java.awt.datatransfer.StringSelection;
import java.awt.datatransfer.UnsupportedFlavorException;
import java.io.IOException;
public class Test {
public static void main(String[] args) throws HeadlessException,
UnsupportedFlavorException, IOException {
Toolkit.getDefaultToolkit().getSystemClipboard()
.setContents(new StringSelection("hi there"), null);
System.out.println(((String) Toolkit.getDefaultToolkit()
.getSystemClipboard().getData(DataFlavor.stringFlavor)));
}
}

import java.awt.Toolkit;
import java.awt.datatransfer.StringSelection;
import java.awt.datatransfer.Clipboard;
public class tester{
public static void main(String[] args){
// from string to clipboard
StringSelection selection = new StringSelection("hi");
Clipboard clipboard = Toolkit.getDefaultToolkit().getSystemClipboard();
clipboard.setContents(selection, selection);
}
}
This program does it. It will set the String "hi" to clipboard. You can change it to a variable.

Linux cut and paste is a bit weird these days, because there are at least two different ways of doing it. In short, sometimes it's better to just paste with the middle button, and other times it's better to control-v, and sometimes neither seems to work.
Running autocutsel as a background process seems to help.
http://www.nongnu.org/autocutsel/