Eu estudo JAVA, e decidi desenvolver uma calculadora básica que ainda penso em otimizá-la e melhorá-la, estou enviando se quiserem dar uma olhada e, se quiserem me ajudar a melhorar o programa para cálculos maiores, ou implementação do zero (o que não consegui no momento) ou uma dica de otimização, enfim, é só um exercício mental que estou fazendo para me acostumar melhor com o Java.

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package soma;

/**
 *
 * @author Neozito
 */
public class TelaSoma extends javax.swing.JFrame {

    private int numero;
    private int numerodois;
    private int resultado;
    private float resultadodois;
    
    public TelaSoma() {
        
 
        
        
        initComponents();
    }

    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {

        btn1 = new javax.swing.JButton();
        btn2 = new javax.swing.JButton();
        btn3 = new javax.swing.JButton();
        btn4 = new javax.swing.JButton();
        btn5 = new javax.swing.JButton();
        btn6 = new javax.swing.JButton();
        btn7 = new javax.swing.JButton();
        btn8 = new javax.swing.JButton();
        btn9 = new javax.swing.JButton();
        lblTela = new javax.swing.JLabel();
        btnMenos = new javax.swing.JButton();
        btnSoma = new javax.swing.JButton();
        btnDivisao = new javax.swing.JButton();
        btnVezes = new javax.swing.JButton();
        lblTela2 = new javax.swing.JLabel();
        btnCE = new javax.swing.JButton();
        btn10 = new javax.swing.JButton();
        lblTela3 = new javax.swing.JLabel();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        btn1.setText("1");
        btn1.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btn1ActionPerformed(evt);
            }
        });

        btn2.setText("2");
        btn2.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btn2ActionPerformed(evt);
            }
        });

        btn3.setText("3");
        btn3.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btn3ActionPerformed(evt);
            }
        });

        btn4.setText("4");
        btn4.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btn4ActionPerformed(evt);
            }
        });

        btn5.setText("5");
        btn5.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btn5ActionPerformed(evt);
            }
        });

        btn6.setText("6");
        btn6.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btn6ActionPerformed(evt);
            }
        });

        btn7.setText("7");
        btn7.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btn7ActionPerformed(evt);
            }
        });

        btn8.setText("8");
        btn8.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btn8ActionPerformed(evt);
            }
        });

        btn9.setText("9");
        btn9.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btn9ActionPerformed(evt);
            }
        });

        btnMenos.setText("-");
        btnMenos.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btnMenosActionPerformed(evt);
            }
        });

        btnSoma.setText("+");
        btnSoma.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btnSomaActionPerformed(evt);
            }
        });

        btnDivisao.setText("\\");
            btnDivisao.addActionListener(new java.awt.event.ActionListener() {
                public void actionPerformed(java.awt.event.ActionEvent evt) {
                    btnDivisaoActionPerformed(evt);
                }
            });

            btnVezes.setText("x");
            btnVezes.addActionListener(new java.awt.event.ActionListener() {
                public void actionPerformed(java.awt.event.ActionEvent evt) {
                    btnVezesActionPerformed(evt);
                }
            });

            btnCE.setText("CE");
            btnCE.addActionListener(new java.awt.event.ActionListener() {
                public void actionPerformed(java.awt.event.ActionEvent evt) {
                    btnCEActionPerformed(evt);
                }
            });

            btn10.setText("10");
            btn10.addActionListener(new java.awt.event.ActionListener() {
                public void actionPerformed(java.awt.event.ActionEvent evt) {
                    btn10ActionPerformed(evt);
                }
            });

            javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
            getContentPane().setLayout(layout);
            layout.setHorizontalGroup(
                layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addGroup(layout.createSequentialGroup()
                    .addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                    .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                        .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING, false)
                            .addGroup(javax.swing.GroupLayout.Alignment.LEADING, layout.createSequentialGroup()
                                .addComponent(btn4, javax.swing.GroupLayout.PREFERRED_SIZE, 43, javax.swing.GroupLayout.PREFERRED_SIZE)
                                .addGap(18, 18, 18)
                                .addComponent(btn5, javax.swing.GroupLayout.PREFERRED_SIZE, 43, javax.swing.GroupLayout.PREFERRED_SIZE)
                                .addGap(18, 18, 18)
                                .addComponent(btn6, javax.swing.GroupLayout.PREFERRED_SIZE, 43, javax.swing.GroupLayout.PREFERRED_SIZE))
                            .addGroup(layout.createSequentialGroup()
                                .addComponent(btn7, javax.swing.GroupLayout.PREFERRED_SIZE, 43, javax.swing.GroupLayout.PREFERRED_SIZE)
                                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                                .addComponent(btn8, javax.swing.GroupLayout.PREFERRED_SIZE, 43, javax.swing.GroupLayout.PREFERRED_SIZE)
                                .addGap(18, 18, 18)
                                .addComponent(btn9, javax.swing.GroupLayout.PREFERRED_SIZE, 43, javax.swing.GroupLayout.PREFERRED_SIZE))
                            .addGroup(javax.swing.GroupLayout.Alignment.LEADING, layout.createSequentialGroup()
                                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                                    .addGroup(layout.createSequentialGroup()
                                        .addComponent(btn1, javax.swing.GroupLayout.PREFERRED_SIZE, 43, javax.swing.GroupLayout.PREFERRED_SIZE)
                                        .addGap(18, 18, 18)
                                        .addComponent(btn2, javax.swing.GroupLayout.PREFERRED_SIZE, 43, javax.swing.GroupLayout.PREFERRED_SIZE)
                                        .addGap(22, 22, 22))
                                    .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
                                        .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING)
                                            .addGroup(layout.createSequentialGroup()
                                                .addComponent(btnSoma)
                                                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                                                .addComponent(btnCE))
                                            .addGroup(javax.swing.GroupLayout.Alignment.LEADING, layout.createSequentialGroup()
                                                .addGap(4, 4, 4)
                                                .addComponent(btnMenos)
                                                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                                                .addComponent(btn10, javax.swing.GroupLayout.PREFERRED_SIZE, 47, javax.swing.GroupLayout.PREFERRED_SIZE)))
                                        .addGap(18, 18, 18)))
                                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                                    .addComponent(btn3, javax.swing.GroupLayout.PREFERRED_SIZE, 43, javax.swing.GroupLayout.PREFERRED_SIZE)
                                    .addComponent(btnVezes)
                                    .addComponent(btnDivisao))))
                        .addGroup(layout.createSequentialGroup()
                            .addComponent(lblTela, javax.swing.GroupLayout.PREFERRED_SIZE, 69, javax.swing.GroupLayout.PREFERRED_SIZE)
                            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
                            .addComponent(lblTela2, javax.swing.GroupLayout.PREFERRED_SIZE, 69, javax.swing.GroupLayout.PREFERRED_SIZE)
                            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
                            .addComponent(lblTela3, javax.swing.GroupLayout.PREFERRED_SIZE, 33, javax.swing.GroupLayout.PREFERRED_SIZE))))
            );
            layout.setVerticalGroup(
                layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addGroup(layout.createSequentialGroup()
                    .addContainerGap()
                    .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                        .addComponent(lblTela2, javax.swing.GroupLayout.Alignment.TRAILING, javax.swing.GroupLayout.PREFERRED_SIZE, 24, javax.swing.GroupLayout.PREFERRED_SIZE)
                        .addComponent(lblTela3, javax.swing.GroupLayout.Alignment.TRAILING, javax.swing.GroupLayout.PREFERRED_SIZE, 24, javax.swing.GroupLayout.PREFERRED_SIZE)
                        .addComponent(lblTela, javax.swing.GroupLayout.Alignment.TRAILING, javax.swing.GroupLayout.PREFERRED_SIZE, 20, javax.swing.GroupLayout.PREFERRED_SIZE))
                    .addGap(18, 18, 18)
                    .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                        .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
                            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                                .addComponent(btn9, javax.swing.GroupLayout.PREFERRED_SIZE, 58, javax.swing.GroupLayout.PREFERRED_SIZE)
                                .addComponent(btn8, javax.swing.GroupLayout.PREFERRED_SIZE, 58, javax.swing.GroupLayout.PREFERRED_SIZE)
                                .addComponent(btn7, javax.swing.GroupLayout.PREFERRED_SIZE, 58, javax.swing.GroupLayout.PREFERRED_SIZE))
                            .addGap(18, 18, 18)
                            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                                .addComponent(btn4, javax.swing.GroupLayout.PREFERRED_SIZE, 58, javax.swing.GroupLayout.PREFERRED_SIZE)
                                .addComponent(btn5, javax.swing.GroupLayout.PREFERRED_SIZE, 58, javax.swing.GroupLayout.PREFERRED_SIZE)
                                .addComponent(btn6, javax.swing.GroupLayout.PREFERRED_SIZE, 58, javax.swing.GroupLayout.PREFERRED_SIZE))
                            .addGap(18, 18, 18)
                            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                                .addComponent(btn1, javax.swing.GroupLayout.PREFERRED_SIZE, 58, javax.swing.GroupLayout.PREFERRED_SIZE)
                                .addComponent(btn2, javax.swing.GroupLayout.PREFERRED_SIZE, 58, javax.swing.GroupLayout.PREFERRED_SIZE)
                                .addComponent(btn3, javax.swing.GroupLayout.PREFERRED_SIZE, 58, javax.swing.GroupLayout.PREFERRED_SIZE))
                            .addGap(18, 18, 18)
                            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING)
                                .addComponent(btn10, javax.swing.GroupLayout.PREFERRED_SIZE, 53, javax.swing.GroupLayout.PREFERRED_SIZE)
                                .addComponent(btnDivisao)))
                        .addComponent(btnMenos, javax.swing.GroupLayout.Alignment.TRAILING))
                    .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                        .addGroup(layout.createSequentialGroup()
                            .addGap(32, 32, 32)
                            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                                .addComponent(btnVezes)
                                .addComponent(btnSoma)))
                        .addGroup(layout.createSequentialGroup()
                            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
                            .addComponent(btnCE)))
                    .addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
            );

            pack();
        }// </editor-fold>                        

    private void btn1ActionPerformed(java.awt.event.ActionEvent evt) {                                     

        if (numero <= 0){
            numero = 1;
        lblTela.setText(Integer.toString(numero));
   
        }
        else {
            numerodois = 1;
        lblTela.setText(Integer.toString(numero));
        lblTela2.setText(Integer.toString(numerodois));
        }
    }                                    

    private void btn2ActionPerformed(java.awt.event.ActionEvent evt) {                                     
        
        if(numero <= 0){
            numero = 2;
            {
        lblTela.setText(Integer.toString(numero));
        }
        }
        else{
            numerodois = 2;
            {
        lblTela.setText(Integer.toString(numero));
        lblTela2.setText(Integer.toString(numerodois));
        }
        }
    }                                    

    private void btn3ActionPerformed(java.awt.event.ActionEvent evt) {                                     
        // TODO add your handling code here:
        
        if(numero <= 0){
            numero = 3;
            lblTela.setText(Integer.toString(numero));
        }
        else{
            numerodois = 3;
            lblTela.setText(Integer.toString(numero));
             lblTela2.setText(Integer.toString(numerodois));
        }
        
    }                                    

    private void btn4ActionPerformed(java.awt.event.ActionEvent evt) {                                     
        // TODO add your handling code here:
        
        if(numero <= 0){
            numero = 4;
            lblTela.setText(Integer.toString(numero));
        }
        else{
            numerodois = 4;
            lblTela.setText(Integer.toString(numero));
             lblTela2.setText(Integer.toString(numerodois));
        }
    }                                    

    private void btn5ActionPerformed(java.awt.event.ActionEvent evt) {                                     
        // TODO add your handling code here:
        
                
        if(numero <= 0){
            numero = 5;
            lblTela.setText(Integer.toString(numero));
        }
        else{
            numerodois = 5;
            lblTela.setText(Integer.toString(numero));
             lblTela2.setText(Integer.toString(numerodois));
        }
        
    }                                    

    private void btn6ActionPerformed(java.awt.event.ActionEvent evt) {                                     

                
        if(numero <= 0){
            numero = 6;
            lblTela.setText(Integer.toString(numero));
        }
        else{
            numerodois = 6;
            lblTela.setText(Integer.toString(numero));
             lblTela2.setText(Integer.toString(numerodois));
        }
        
    }                                    

    private void btn7ActionPerformed(java.awt.event.ActionEvent evt) {                                     

                
        if(numero <= 7){
            numero = 3;
            lblTela.setText(Integer.toString(numero));
        }
        else{
            numerodois = 7;
            lblTela.setText(Integer.toString(numero));
             lblTela2.setText(Integer.toString(numerodois));
        }
    }                                    

    private void btn8ActionPerformed(java.awt.event.ActionEvent evt) {                                     

                
        if(numero <= 0){
            numero = 8;
            lblTela.setText(Integer.toString(numero));
        }
        else{
            numerodois = 8;
            lblTela.setText(Integer.toString(numero));
             lblTela2.setText(Integer.toString(numerodois));
        }
    }                                    

    private void btn9ActionPerformed(java.awt.event.ActionEvent evt) {                                     
  
                
        if(numero <= 0){
            numero = 9;
            lblTela.setText(Integer.toString(numero));
        }
        else{
            numerodois = 9;
            lblTela.setText(Integer.toString(numero));
             lblTela2.setText(Integer.toString(numerodois));
        }
    }                                    

    private void btnCEActionPerformed(java.awt.event.ActionEvent evt) {                                      
 
        numero = 0;
        numerodois = 0;
        resultado = 0;
        lblTela.setText(null);
        lblTela2.setText(null);
        lblTela3.setText(null);
    }                                     

    private void btn10ActionPerformed(java.awt.event.ActionEvent evt) {                                      
 
        if (numero <= 0){
            numero = 10;
            lblTela.setText(Integer.toString(numero));
        }
        else{
            numerodois = 10;
            lblTela.setText(Integer.toString(numero));
            lblTela2.setText(Integer.toString(numerodois));
        }
      
    }                                     

    private void btnMenosActionPerformed(java.awt.event.ActionEvent evt) {                                         
        
        resultado = numero - numerodois;
        lblTela3.setText(Integer.toString(resultado));
        if (numerodois <= 0){
            lblTela3.setText(null);
        }
    }                                        

    private void btnSomaActionPerformed(java.awt.event.ActionEvent evt) {                                        

                resultado = numero + numerodois;
        lblTela3.setText(Integer.toString(resultado));
        if (numerodois <= 0){
            lblTela3.setText(null);
        }
    }                                       

    private void btnDivisaoActionPerformed(java.awt.event.ActionEvent evt) {                                           
 
        resultadodois = (float) numero/ (float) numerodois;
        lblTela3.setText (Float.toString(resultadodois));
         if (numerodois <= 0){
            lblTela3.setText(null);
        }
    }                                          

    private void btnVezesActionPerformed(java.awt.event.ActionEvent evt) {                                         

        resultado = numero * numerodois;
        lblTela3.setText(Integer.toString(resultado));
         if (numerodois <= 0){
            lblTela3.setText(null);
        }
    }                                        
    

    public static void main(String args[]) {
        /* Set the Nimbus look and feel */        //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
        /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
         * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
         */
        try {
            for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
                if ("Nimbus".equals(info.getName())) {
                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (ClassNotFoundException ex) {
            java.util.logging.Logger.getLogger(TelaSoma.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(TelaSoma.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(TelaSoma.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(TelaSoma.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }
        //</editor-fold>


        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new TelaSoma().setVisible(true);
            }
        });
    }

    // Variables declaration - do not modify                     
    private javax.swing.JButton btn1;
    private javax.swing.JButton btn10;
    private javax.swing.JButton btn2;
    private javax.swing.JButton btn3;
    private javax.swing.JButton btn4;
    private javax.swing.JButton btn5;
    private javax.swing.JButton btn6;
    private javax.swing.JButton btn7;
    private javax.swing.JButton btn8;
    private javax.swing.JButton btn9;
    private javax.swing.JButton btnCE;
    private javax.swing.JButton btnDivisao;
    private javax.swing.JButton btnMenos;
    private javax.swing.JButton btnSoma;
    private javax.swing.JButton btnVezes;
    private javax.swing.JLabel lblTela;
    private javax.swing.JLabel lblTela2;
    private javax.swing.JLabel lblTela3;
    // End of variables declaration                   
}

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