Exercicio 1 feito

import java.awt.BorderLayout;
import java.awt.GridLayout;
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.HashSet;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JButton;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingConstants;

public class Conversor extends JFrame implements ActionListener{
    JTextField texto;
    JButton btnTamanho, btnMaius, btnMinus, btnLimpar;
    JLabel txtEntrada, txtTamanho, txtIam;
    JTextField txtCont1, txtCont2, txtCont3;

    public void actionPerformed (ActionEvent e) {
        if (e.getSource() == btnLimpar) {
            texto.setText("");
        }
        if (e.getSource() == btnTamanho) {
            int tam = texto.getText().length();
            txtIam.setText(String.format("%d", tam));
        }
        if (e.getSource() == btnMaius) {
            texto.setText(String.format("%s", texto.getText().toUpperCase()));
        }
        if (e.getSource() == btnMinus) {
            texto.setText(String.format("%s", texto.getText().toLowerCase()));
        }
    }
    public Conversor() {
        setLayout(new BorderLayout());
        btnTamanho = new JButton ("Tamanho");
        btnMaius = new JButton ("Maiusculo");
        btnMinus = new JButton ("Minusculo");
        btnLimpar = new JButton ("Limpar");
        JPanel sul = new JPanel (new GridLayout(5,1));
        sul.add(btnTamanho);
        sul.add(btnMaius);
        sul.add(btnMinus);
        sul.add(btnLimpar);
        add (sul, BorderLayout.SOUTH);

        JPanel centro = new JPanel (new GridLayout (5,1));
        txtEntrada = new JLabel ("Digite um texto:   ", SwingConstants.RIGHT); //try left
        txtTamanho = new JLabel ("Tamanho:    ", SwingConstants.RIGHT);
        txtIam = new JLabel ("", SwingConstants.RIGHT);
        texto = new JTextField (5);
        centro.add(txtEntrada);
        centro.add(texto);
        centro.add(txtTamanho);
        centro.add(txtIam);
        add(centro, BorderLayout.CENTER);
        btnTamanho.addActionListener(this);
        btnMaius.addActionListener(this);
        btnMinus.addActionListener(this);
        btnLimpar.addActionListener(this);
    }
    public static void main(String[] args) {
        Conversor tela = new Conversor();
        tela.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        tela.setSize(350, 250);
        tela.setLocation(500,500);
        tela.setVisible(true);
    }
}