Voilà un exemple d'affichage

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import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class calculette implements ActionListener
{

JTextArea affichage;

public calculette()
{

JFrame all = new JFrame("Calculatrice" );

JPanel back = new JPanel();
JPanel clavier = new JPanel();
JPanel operation = new JPanel();
JPanel clavscien= new JPanel();
JPanel egal=new JPanel();

egal.setLayout(new BorderLayout());
back.setLayout(new BorderLayout());
operation.setLayout(new GridLayout(4,1));
clavscien.setLayout(new GridLayout(2,1));
clavier.setLayout(new GridLayout(4,3));

JButton t1 = new JButton("1" );
t1.addActionListener(this);
JButton t2 = new JButton("2" );
t2.addActionListener(this);
JButton t3 = new JButton("3" );
t3.addActionListener(this);
JButton t4 = new JButton("4" );
t4.addActionListener(this);
JButton t5 = new JButton("5" );
t5.addActionListener(this);
JButton t6 = new JButton("6" );
t6.addActionListener(this);
JButton t7 = new JButton("7" );
t7.addActionListener(this);
JButton t8 = new JButton("8" );
t8.addActionListener(this);
JButton t9 = new JButton("9" );
t9.addActionListener(this);
JButton t10 = new JButton("0" );
t10.addActionListener(this);
JButton t11 = new JButton("," );
t11.addActionListener(this);
JButton t12 = new JButton("-" );
t12.addActionListener(this);
JButton plus = new JButton("+" );
plus.addActionListener(this);
JButton moins = new JButton("-" );
moins.addActionListener(this);
JButton fois = new JButton("*" );
fois.addActionListener(this);
JButton divise = new JButton("/" );
divise.addActionListener(this);
JButton carre = new JButton("²" );
carre.addActionListener(this);
JButton cube = new JButton("³" );
cube.addActionListener(this);
JButton tegal = new JButton("=" );
tegal.addActionListener(this);

clavier.add(t1); clavier.add(t2); clavier.add(t3);
clavier.add(t4); clavier.add(t5); clavier.add(t6);
clavier.add(t7); clavier.add(t8); clavier.add(t9);
clavier.add(t10); clavier.add(t11); clavier.add(t12);

clavscien.add(carre);
clavscien.add(cube);
operation.add(plus);
operation.add(moins);
operation.add(divise);
operation.add(fois);
affichage= new JTextArea();
affichage.setLayout(new BorderLayout());
egal.add(tegal);
back.add(affichage,BorderLayout.NORTH);
back.add(operation,BorderLayout.WEST);
back.add(clavier,BorderLayout.CENTER);
back.add(clavscien,BorderLayout.EAST);
back.add(egal,BorderLayout.SOUTH);
all.setContentPane(back);
all.setVisible(true);
all.pack();
}

public void actionPerformed(ActionEvent evt)
{
String a = evt.getActionCommand();
affichage.setText(a);
}

}

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