Hi, I created a program using the linkedlist package. I encountered an error when I tried to insert an element... By the way here's my code...

import javax.swing.*;
import java.awt.event.*;
import java.awt.*;
import java.util.*;
class guiListOperations3 extends JFrame implements ActionListener
{
	static LinkedList <String> list=new LinkedList <String>();
	static JLabel lblElement,lblDisplay,lblPos;
	static JTextField txtInput1,txtDisplay1,txtDisplay2,txtPos;
	static JButton btnAdd,btnRemove,btnPeek,btnCancel,btnClear;
	static int pos=0;
	public guiListOperations3()
	{
		Container drum=getContentPane();
		drum.setLayout(new FlowLayout());

		lblElement=new JLabel("Enter Element: ");
		drum.add(lblElement);

		txtInput1=new JTextField(10);
		drum.add(txtInput1);

		lblDisplay=new JLabel("List: ");
		drum.add(lblDisplay);

		txtDisplay1=new JTextField(10);
		txtDisplay1.setEditable(false);
		drum.add(txtDisplay1);

		lblPos=new JLabel("Position:");
		drum.add(lblPos);

		txtPos=new JTextField(1);
		drum.add(txtPos);

		btnAdd=new JButton("Insert");
		drum.add(btnAdd);

		lblDisplay=new JLabel("To delete element:");
		drum.add(lblDisplay);

		btnRemove=new JButton("Remove");
		drum.add(btnRemove);

		lblDisplay=new JLabel("To view element:");
		drum.add(lblDisplay);

		btnPeek=new JButton("Peek");
		drum.add(btnPeek);

		lblDisplay=new JLabel("--------------------");
		drum.add(lblDisplay);

		btnClear=new JButton("Clear");
		drum.add(btnClear);

		btnCancel=new JButton("Cancel");
		drum.add(btnCancel);

		setSize(165,360);
		setLocation(600,300);
		setVisible(true);

		btnAdd.addActionListener(this);
		btnRemove.addActionListener(this);
		btnPeek.addActionListener(this);
		btnClear.addActionListener(this);
		btnCancel.addActionListener(this);
	}

	public void actionPerformed(ActionEvent a)
	{
		String b;
		if(a.getSource()==btnAdd)
			if(txtInput1.getText().equals("")||txtInput1.getText().equals(null))
				JOptionPane.showMessageDialog(null,"Invalid Entry!","Error",0);
			else
			{
				pos=Integer.parseInt(txtPos.getText());
				list.add(txtInput1.getText(),pos);
				txtDisplay1.setText(""+list);
			}
		if(a.getSource()==btnRemove)
			if((txtDisplay1.getText().equals(null))||(txtDisplay1.getText().equals(""))||(txtDisplay1.getText().equals("[]")))
			{
				JOptionPane.showMessageDialog(null,"List is empty!","Error",0);
			}
			else
			{
			list.remove();
			txtDisplay1.setText(""+list);
			}
		if(a.getSource()==btnPeek)
		if((txtDisplay1.getText().equals(null))||(txtDisplay1.getText().equals(""))||(txtDisplay1.getText().equals("[]")))
			{
				JOptionPane.showMessageDialog(null,"Error! List is empty!","Error",0);
			}
			else
			JOptionPane.showMessageDialog(null,"The top value is "+list.peek());
		if(a.getSource()==btnCancel)
		{

			setVisible(false);
			guiMenu z=new guiMenu();
		}
		if(a.getSource()==btnClear)
		{
			txtInput1.setText("");
			txtDisplay1.setText("");
		}
	}

	public static void main(String[]args)
	{
		guiListOperations3 app=new guiListOperations3();
		app.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
	}
}

I hope you can help me find solution and thanks in advance :)

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