how to delete the last digit of a set of numbers

Question

I am still learning in making this calculator program, and much less in it i want to ask how to delete the last digit of a set of numbers

This is my current code :

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

public class frame {
  int num1,num2,ans;

public static void main(String[] args) {
    JFrame gui = new JFrame("Kalkulator");
    final JTextField output = new JTextField(100);
    JPanel panel = new JPanel();
    JButton hapus = new JButton("<-");
    JButton satu = new JButton("1");
    JButton dua = new JButton("2");
    JButton tiga = new JButton("3");
    JButton empat = new JButton("4");
    JButton lima = new JButton("5");
    JButton enam = new JButton("6");
    JButton tujuh = new JButton("7");
    JButton delapan = new JButton("8");
    JButton sembilan = new JButton("9");
    JButton nol = new JButton("0");
    JButton kali = new JButton("X");
    JButton bagi = new JButton("/");
    JButton kurang = new JButton("-");
    JButton tambah = new JButton("+");
    JButton samadengan = new JButton("=");
    JButton titik = new JButton(".");
    JButton clear = new JButton("C");
    JLabel nama = new JLabel("Zulham azwar achmad (5302414040)");

    nama.setHorizontalAlignment(SwingConstants.CENTER);

    output.setBounds(10,11,290,61); //(jarak geser ke-kanan , jarak geser kebawah , panjang , tinggi )
    clear.setBounds(250,121,50,50);
    nama.setBounds(10,77,290,34);
    hapus.setBounds(190,121,50,50);
    satu.setBounds(10, 121, 50, 50);
    dua.setBounds(70,121,50,50);
    tiga.setBounds(130,121,50,50);
    empat.setBounds(10,181,50,50);
    lima.setBounds(70,181,50,50);
    enam.setBounds(130,181,50,50);
    tujuh.setBounds(10,241,50,50);
    delapan.setBounds(70,241,50,50);
    sembilan.setBounds(130,241,50,50);
    nol.setBounds(10,301,110,50);
    titik.setBounds(130,301,50,50);
    kali.setBounds(190,181,50,50);
    bagi.setBounds(190,241,50,50);
    kurang.setBounds(250,181,50,50);
    tambah.setBounds(250,241,50,50);
    samadengan.setBounds(190,301,110,50);

    panel.setLayout(null);
    panel.add(output);
    panel.add(hapus);
    panel.add(satu);
    panel.add(dua);
    panel.add(tiga);
    panel.add(empat);
    panel.add(lima);
    panel.add(enam);
    panel.add(tujuh);
    panel.add(delapan);
    panel.add(sembilan);
    panel.add(nol);
    panel.add(titik);
    panel.add(kali);
    panel.add(bagi);
    panel.add(tambah);
    panel.add(kurang);
    panel.add(samadengan);
    panel.add(clear);
    panel.add(nama);

    gui.getContentPane().add(panel);
    gui.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    gui.setSize(317,390);
    gui.setVisible(true);
    gui.setResizable(false);

    satu.addActionListener(new ActionListener() {
         public void actionPerformed(ActionEvent e) {
             output.setText(output.getText()+"1");
          }

       }); 
    dua.addActionListener(new ActionListener() {

        public void actionPerformed(ActionEvent e) {
            output.setText(output.getText()+"2");

        }
    });
    tiga.addActionListener(new ActionListener() {

        public void actionPerformed(ActionEvent e) {
            output.setText(output.getText()+"3");

        }
    });
    empat.addActionListener(new ActionListener() {

        public void actionPerformed(ActionEvent e) {
            output.setText(output.getText()+"4");

        }
    });
    lima.addActionListener(new ActionListener() {

        public void actionPerformed(ActionEvent e) {
            output.setText(output.getText()+"5");

        }
    });
    enam.addActionListener(new ActionListener() {

        public void actionPerformed(ActionEvent e) {
            output.setText(output.getText()+"6");

        }
    });
    tujuh.addActionListener(new ActionListener() {

        public void actionPerformed(ActionEvent e) {
            output.setText(output.getText()+"7");

        }
    });
    delapan.addActionListener(new ActionListener() {

        public void actionPerformed(ActionEvent e) {
            output.setText(output.getText()+"8");

        }
    });
    sembilan.addActionListener(new ActionListener() {

        public void actionPerformed(ActionEvent e) {
            output.setText(output.getText()+"9");

        }
    });
    nol.addActionListener(new ActionListener() {

        public void actionPerformed(ActionEvent e) {
            output.setText(output.getText()+"0");

        }
    });
    clear.addActionListener(new ActionListener() {

        public void actionPerformed(ActionEvent e) {
            output.setText(null);

        }
    });
    hapus.addActionListener(new ActionListener() {

        public void actionPerformed(ActionEvent e) {
            output.setText(); <-- how to backspace ? 

        }
    });

   }                              
 }

Answer 1

According to Docs Java Documentation

*Chars beginning at start

*str.substring(start, end)

*Up to but not including end

There is a more complex version of substring() that takes both start and end index numbers: substring(int start, int end) returns a string of the chars beginning at the start index number and running up to but not including the end index.

Examples:

String str = "Hello";
String a = str.substring(2, 4);  // a is "ll" (not "llo")
String b = str.substring(0, 3);  // b is "Hel"
String c = str.substring(4, 5);  // c is "o" -- the last char

Take a look at ideone code live

  hapus.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            String text = output.getText();
            output.setText(0,text.length()-2));//will return all string but the last one
        }
    });

Answer 2

You can do something likewise,

 hapus.addActionListener(new ActionListener() {

        public void actionPerformed(ActionEvent e) {
            if(output.getText().length()>0){
                output.setText(output.getText().substring(0,output.getText().length()-1));
            }

        }
    });

Answer 3

You can use substring method like this :

 String strwithoutLastDigit = someString.substring(0,someString.length()-1)

Answer 4

You can use substring :

hapus.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent e) {
        String text = output.getText();
        output.setText(text.substring(0,text.length()-1));
    }
});