I am student practicing JAVA for few first times. We were asked to create a simple calculator. I've done everything without any error. My Only problem is that when I do a 1.66 + 55 for example or even 5 + 6 it shows that error in title. Here is the coede
import java.awt.BorderLayout;
public class Frame2 extends JFrame {
private JPanel contentPane;
private JTextField tot;
public String operateur = ""; 
public String s;
public String Value = "";
public String Value2 = "";
public Double Total = 0.0;
/**
 * Launch the application.
 */
public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
        public void run() {
            try {
                Frame2 frame = new Frame2();
                frame.setVisible(true);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    });
}
/**
 * Create the frame.
 */
public Frame2() {
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setBounds(100, 100, 267, 360);
    contentPane = new JPanel();
    contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
    setContentPane(contentPane);
    contentPane.setLayout(null);
    tot = new JTextField();
    tot.setFont(new Font("Tahoma", Font.PLAIN, 18));
    tot.setEditable(false);
    tot.setBounds(10, 11, 231, 45);
    contentPane.add(tot);
    tot.setColumns(10);
    JButton t7 = new JButton("7");
    t7.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            if (operateur == "") { 
            Value = Value.trim() + 7;
            } else {
            Value2 = Value2.trim() + 7;
            }
            s = tot.getText();
            tot.setText(s+"7");
        }
    });
    t7.setBounds(10, 67, 49, 41);
    contentPane.add(t7);
    JButton t8 = new JButton("8");
    t8.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            if (operateur == "") { 
            Value = Value.trim() + 8;
            } else {
            Value2 = Value2.trim() + 8;
            }
            s = tot.getText();
            tot.setText(s+"8");
        }
    });
    t8.setBounds(69, 67, 50, 41);
    contentPane.add(t8);
    JButton t9 = new JButton("9");
    t9.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            if (operateur == "") { 
            Value = Value.trim() + 9;
            } else {
            Value2 = Value2.trim() + 9;
            }
            s = tot.getText();
            tot.setText(s+"9");
        }
    });
    t9.setBounds(129, 67, 50, 41);
    contentPane.add(t9);
    JButton t4 = new JButton("4");
    t4.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            if (operateur == "") { 
            Value = Value.trim() + 4;
            } else {
            Value2 = Value2.trim() + 4;
            }
            s = tot.getText();
            tot.setText(s+"4");
        }
    });
    t4.setBounds(10, 119, 50, 41);
    contentPane.add(t4);
    JButton t5 = new JButton("5");
    t5.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            if (operateur == "") { 
            Value = Value.trim() + 5;
            } else {
            Value2 = Value2.trim() + 5;
            }
            s = tot.getText();
            tot.setText(s+"5");
        }
    });
    t5.setBounds(69, 119, 50, 41);
    contentPane.add(t5);
    JButton t6 = new JButton("6");
    t6.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            if (operateur == "") { 
            Value = Value.trim() + 6.0;
            } else {
            Value2 = Value2.trim() + 6.0;
            }
            s = tot.getText();
            tot.setText(s+"6");
        }
    });
    t6.setBounds(129, 119, 50, 41);
    contentPane.add(t6);
    JButton t3 = new JButton("3");
    t3.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            if (operateur == "") { 
            Value = Value.trim() + 3.0;
            } else {
            Value2 = Value2.trim() + 3.0;
            }
            s = tot.getText();
            tot.setText(s+"3");
        }
    });
    t3.setBounds(10, 173, 49, 39);
    contentPane.add(t3);
    JButton t2 = new JButton("2");
    t2.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            if (operateur == "") { 
            Value = Value.trim() + 2;
            } else {
            Value2 = Value2.trim() + 2;
            }
            s = tot.getText();
            tot.setText(s+"2");
        }
    });
    t2.setBounds(69, 171, 50, 41);
    contentPane.add(t2);
    JButton t1 = new JButton("1");
    t1.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            if (operateur == "") { 
            Value = Value + 1;
            } else if (operateur != null) {
            Value2 = Value2.trim() + 1;
            }
            s = tot.getText();
            tot.setText(s+"1");
        }
    });
    t1.setBounds(129, 171, 49, 41);
    contentPane.add(t1);
    JButton t0 = new JButton("0");
    t0.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            if (operateur == "") { 
            Value = Value.trim() + 0;
            } else {
            Value2 = Value2.trim() + 0;
            }
            s = tot.getText();
            tot.setText(s+"0");
        }
    });
    t0.setBounds(129, 221, 50, 41);
    contentPane.add(t0);
    JButton virg = new JButton(",");
    virg.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            if (operateur == "") { 
                Value = Value.trim() + ".";
                } else {
                Value2 = Value2.trim() + ".";
                }
                s = tot.getText();
                tot.setText(s+".");
        }
    });
    virg.setBounds(69, 223, 50, 39);
    contentPane.add(virg);
    JButton btnC = new JButton("C");
    btnC.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            tot.setText("");
            operateur = "";
            Value = "";
            Value2 = "";
            Total = 0.0;
        }
    });
    btnC.setForeground(Color.RED);
    btnC.setBounds(10, 223, 49, 41);
    contentPane.add(btnC);
    JButton plus = new JButton("+");
    plus.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            operateur ="+";
            s = tot.getText();
            tot.setText(s +"+");
        }
    });
    plus.setBounds(188, 67, 53, 41);
    contentPane.add(plus);
    JButton calc = new JButton("CALCULER");
    calc.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            if (operateur == "+") {
            Total = Double.valueOf(Value) + Double.valueOf(Value2);
            Total = Math.round( Total * 100.0 ) / 100.0;
            tot.setText(String.valueOf(Total));
        }
        else if (operateur=="-") {
            Total = Double.valueOf(Value) - Double.valueOf(Value2);
            Total = Math.round( Total * 100.0 ) / 100.0;
            tot.setText(String.valueOf(Total));
        }
        else if (operateur=="*") {
            Total = Double.valueOf(Value) * Double.valueOf(Value2);
            Total = Math.round( Total * 100.0 ) / 100.0;
            tot.setText(String.valueOf(Total));
        }
        else if (operateur=="/") {
            Total = Double.valueOf(Value) / Double.valueOf(Value2);
            Total = Math.round( Total * 100.0 ) / 100.0;
            tot.setText(String.valueOf(Total));
        }
            Value = String.valueOf(Total);
            Value2 = "";
            operateur = "";
            Total = 0.0;
        }
    });
    calc.setBounds(10, 273, 231, 38);
    contentPane.add(calc);
    JButton moins = new JButton("-");
    moins.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            operateur ="-";
            s = tot.getText();
            tot.setText(s+"-");
        }
    });
    moins.setBounds(189, 119, 52, 41);
    contentPane.add(moins);
    JButton fois = new JButton("*");
    fois.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            operateur ="*";
            s = tot.getText();
            tot.setText(s+"*");
        }
    });
    fois.setBounds(188, 173, 53, 39);
    contentPane.add(fois);
    JButton sur = new JButton("/");
    sur.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            operateur ="/";
            s = tot.getText();
            tot.setText(s+"/");
        }
    });
    sur.setBounds(189, 221, 52, 41);
    contentPane.add(sur);
}
}
 
     
    