I can't convert Binary to Decimal, Decimal to Binary

Question

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

public class BinaryGUI extends BinaryGUIDemo {


        public static void main(String[] args) {
            new BinaryGUI();
        }

        private JFrame frame;
        private JButton button;
        private JTextField text;
        private JTextField text2;
        private String decimalnumber = null;

        public BinaryGUI() {
            
            frame = new JFrame("Conversion!");

            JLabel label = new JLabel("Binary:");
            frame.setLayout(new FlowLayout());
            frame.add(label);

            text = new JTextField(15);
            frame.add(text);

            JLabel label2 = new JLabel("Decimal:");
            frame.add(label2);

            text2 = new JTextField(15);
            frame.add(text2);

            
            button = new JButton("Convert");
            button.addActionListener(new ButtonListener());
            frame.add(button);
            
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.setSize(250, 300);
            frame.setLocationRelativeTo(null);
            frame.setVisible(true);
        }

        public void Convert() {
            String binary = text.getText();
            int i;
            for (i = 0; i < binary.length(); i++) {
                char select = binary.charAt(binary.length() - i - 1);
                char number = (char) (select * Math.pow(2, i)); 
                decimalnumber += number;
            }
        }
        public class ButtonListener implements ActionListener {
            public void actionPerformed(ActionEvent e) {
                Convert();
                if (button.getText().equals("Convert")) {
                    text2.setText(decimalnumber);
                    text.getText();
                    text2.getText();
                } else {
                }
            }
        }
    }

I can run the program but for some reason it shows/ puts random characters instead of the initial value of the binary and I cant seem to run the program decimal back to binary. how can I improve this codes. To make it clear it does not convert binary to decimal, and how will I convert it back decimal to binary and if there is some codes that would help me, would be very appreciated.

Answer 1

You are almost there, your problem is from the conversion from char to int. Characters in Java are stored in UTF-16 unicode. This means that under the hood the bit pattern does not match the value on screen. https://naveenr.net/unicode-character-set-and-utf-8-utf-16-utf-32-encoding/

So when you read in a char 1 this gets converted to number 49, 0 gets converted to 48

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

public class BinaryGUI {

    public static void main(String[] args) {
        new BinaryGUI();
    }

    private JFrame frame;
    private JButton button;
    private JTextField text;
    private JTextField text2;
    private int decimalnumber = 0;

    public BinaryGUI() {

        frame = new JFrame("Conversion!");

        JLabel label = new JLabel("Binary:");
        frame.setLayout(new FlowLayout());
        frame.add(label);

        text = new JTextField(15);
        frame.add(text);

        JLabel label2 = new JLabel("Decimal:");
        frame.add(label2);

        text2 = new JTextField(15);
        frame.add(text2);

        button = new JButton("Convert");
        button.addActionListener(new ButtonListener());
        frame.add(button);

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(250, 300);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    public void Convert() {
        String binary = text.getText();
        decimalnumber = 0;
        int i;
        for (i = 0; i < binary.length(); i++) {
            char select = binary.charAt(binary.length() - i - 1);
            System.out.println((int) select); // outputs the char as an int
            int number = (int) ((select - 48) * Math.pow(2, i));
            decimalnumber += number;
        }
    }

    public class ButtonListener implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            Convert();

            text2.setText("" + decimalnumber);
            text.getText();
            text2.getText();

        }
    }
}

Note I made decimalnumber an int, then used string concatination to print it out

Answer 2

Convert Binary to Decimal:

int deicimal = 12;
String binaryString = Integer.toBinaryString(deicimal);   // it will be "1100"

Convert Decimal to Binary :

String binaryString = "1100";  
int decimal = Integer.parseInt(binaryString, 2);  // it will be 12