Thread: how to output using JLabel?

here my question...
When user clicks CALCULATE button, display total amount of loan with interest (use JLabel to display the text).
But if user has entered an invalid input (such as character, string or symbol), promt user that he or she has entered an invalid input.

so now, here my code:

package projek;
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
 
public class loan extends JFrame implements ActionListener{
    JButton calculate;
    JTextField pinjaman, interest;
    double hasil;
 
    loan(){
    Container kotak=getContentPane();
    kotak.setLayout(new GridLayout(3,3));
 
    JLabel loanAmount=new JLabel("Jumlah pinjaman");
    kotak.add(loanAmount);
    pinjaman=new JTextField(10);
    kotak.add(pinjaman);
 
    JLabel interesting=new JLabel("Faedah(Riba)");
    kotak.add(interesting);
    interest=new JTextField(10);
    kotak.add(interest);
 
    calculate=new JButton("Kira");
    kotak.add(calculate);
    calculate.addActionListener(this);
 
    JLabel jawapan=new JLabel("Result: TOTAL LOAN WITH INTEREST IS "+hasil);
    kotak.add(jawapan);
 
    setDefaultCloseOperation(EXIT_ON_CLOSE);
    setTitle("LOAN CALCULATION");
    pack();
    show();
    }
 
 
    public void actionPerformed(ActionEvent e){
        Object butangtekan=e.getSource();
        if(butangtekan==calculate){
            try{
             double untukloan=Double.parseDouble(pinjaman.getText());
             double faedah=Double.parseDouble(interest.getText()), riba, hasil;
 
             riba=(faedah*untukloan)/100;
             hasil=riba+untukloan;
 
 
            }
            catch(Exception a){
                JOptionPane.showMessageDialog(null, "Wrong input, must be numeric", "Error",JOptionPane.ERROR_MESSAGE);
            }                  
           }
        }
 
    public static void main(String args[]){
        new loan();
    }
}

so can somebody show me how to input the result(hasil) into the page using JLabel. if got any wrong pls tell me...
sorry for my bad english...

Hi qaromi,

I have made some changes in the program. Please first compile and execute it. I have commented in front of the lines where i have made the changes. Please go through it.

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

public class loan extends JFrame implements ActionListener{
JButton calculate;
JTextField pinjaman, interest;
double hasil;
JLabel loanAmount,interesting,jawapan; //See here i have Declared all the labels globally as we need them for
//the whole class i.e. for all its methods.

loan(){
Container kotak=getContentPane();
kotak.setLayout(new GridLayout(3,3));

loanAmount=new JLabel("Jumlah pinjaman");
kotak.add(loanAmount);
pinjaman=new JTextField(10);
kotak.add(pinjaman);

interesting=new JLabel("Faedah(Riba)");
kotak.add(interesting);
interest=new JTextField(10);
kotak.add(interest);

calculate=new JButton("Kira");
kotak.add(calculate);
calculate.addActionListener(this);

jawapan=new JLabel("Result: TOTAL LOAN WITH INTEREST IS "+hasil);
kotak.add(jawapan);

setDefaultCloseOperation(EXIT_ON_CLOSE);
setTitle("LOAN CALCULATION");
pack();
show();
}


public void actionPerformed(ActionEvent e){
Object butangtekan=e.getSource();
if(butangtekan==calculate){
try{
double untukloan=Double.parseDouble(pinjaman.getText());
double faedah=Double.parseDouble(interest.getText()), riba; //See here i have removed the hasil variable
// as it is already declared globally. so no need
riba=(faedah*untukloan)/100;
hasil=riba+untukloan;
jawapan.setText("Result: TOTAL LOAN WITH INTEREST IS "+hasil); //setText(String) is a method which
// sets the the given text in the given
//component
}
catch(Exception a){
JOptionPane.showMessageDialog(null, "Wrong input, must be numeric", "Error",JOptionPane.ERROR_MESSAGE);
}
}
}

public static void main(String args[]){
loan n=new loan();
}
}

Regards,
guptapr