Thread: Type mismatch: cannot convert from void to JTextField

my gui class:

import java.awt.FlowLayout;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.JPasswordField;
import javax.swing.JOptionPane;
import javax.swing.JButton;
import javax.swing.Icon;
import javax.swing.ImageIcon;
import javax.swing.JOptionPane;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
 
 
public class GUI extends JFrame{
 
	private JTextField tf;
	private Font pf;
	private Font bf;
	private Font itf;
	private Font biff;
	private JRadioButton pb;
	private JRadioButton bb;
	private JRadioButton ib;
	private JRadioButton bib;
	private ButtonGroup group;
 
 
	public GUI(){
		super("The Title");
		setLayout(new FlowLayout());
 
		tf= new JTextField("Nikolai is awesome", 25);
		add(tf);
 
		pb=new JRadioButton("plain", true);
		bb=new JRadioButton("bold", false);
		ib=new JRadioButton("italic", false);
		bib=new JRadioButton("bold and italic", false);
		add(pb);
		add(bb);
		add(ib);
		add(bib);
 
		group=new ButtonGroup();
		group.add(pb);
		group.add(bb);
		group.add(ib);
		group.add(bib);
 
 
		pf=new Font("Serif", Font.PLAIN, 14);
		bf=new Font("Serif", Font.BOLD, 14);
		itf=new Font("Serif", Font.ITALIC, 14);
		biff=new Font("Serif", Font.BOLD + Font.ITALIC, 14);
		tf=setFont(pf);//<--this is the line reference for GUI line 58
 
		pb.addItemListener(new HandlerClass(pf));
		bb.addItemListener(new HandlerClass(bf));
		ib.addItemListener(new HandlerClass(itf));
		bib.addItemListener(new HandlerClass(biff));
	}
	private class HandlerClass implements ItemListener{
		private Font font;
 
		public HandlerClass(Font f){
			font=f;
		}
 
		public void itemStateChanged(ItemEvent event){
			tf.setFont(font);
		}
	}
 
}

eclipse error message:

Exception in thread "main" java.lang.Error: Unresolved compilation problem: 
	Type mismatch: cannot convert from void to JTextField
 
	at GUI.<init>(GUI.java:58)
	at Apples.main(Apples.java:7)

A fix and explanation would be much appreciated. I copied this from a thenewboston tutorial and he uses an old version of java but im pretty sure ive copied character for character!

For issues like this, one of the best places to consult is the API. The line where the error occurs calls setFont for JFrame (which is a parent method of Container):
Container (Java Platform SE 7 )
Looking at the API docs page above - what does this method return? Does your code deal properly with the returned value (if any is returned)?