Thread: Need some help with my basic calculator

Hi all, if someone could help me out with my calculator I would really appreciate it.

So the problem is, that it does the most basic of calculations of multiples, plus and minus, I haven't added division yet, that will come later. If I try 5 * 5 = 25 obviously, but if I try something like 5 * 5 * 5 = 25, it wipes the 1st 5 and calculates the 2nd and 3rd 5. Same thing goes for 5 + 5 + 5 = 10. I need it to be able to do equations like -3 + 5, 4 * 4 + 6, 3 * 2 - 5, etc etc.

Thank you for your time everyone.

import javax.swing.*;
import java.awt.event.*;
import java.awt.*;
import java.util.Scanner;
 
public class CalculatorPanel extends JPanel{
 
  private Calculator calc = new Calculator();
 
  //an array of buttons displayed on the calculator
  private JButton[] digitButtons;
 
  //output display for the calculator
  private JTextField display = new JTextField(10);
 
  //main method - sets up JFrame
  public static void main(String[]args){
 
    JFrame frame = new JFrame("Calculator");
    frame.setContentPane(new CalculatorPanel());
    frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
    frame.pack();
    frame.setVisible(true);
  }
 
  //constructor -- builds a GUI for a calculator
  public CalculatorPanel(){
 
    //create an array of button labels 
    String[] buttonLabels =  {"1", "2", "3", "4", "5", "6",
      "7", "8", "9", "C", "0", "=", "+", "-", "*"};
 
    //create an array of buttons
    digitButtons = new JButton[buttonLabels.length];
 
    //create an actionListener 
    ButtonListener  listener = new ButtonListener();
 
    // Create a 4 x 3 grid for placement of buttons. 
    JPanel buttonGrid = new JPanel();
    buttonGrid.setLayout(new GridLayout(5, 3));
 
    //create a button with each button label, add it to buttonGrid, and register the button as a listener
    for (int nextBut = 0; nextBut < digitButtons.length; nextBut++){
      digitButtons[nextBut] = new JButton(buttonLabels[nextBut]);
      buttonGrid.add(digitButtons[nextBut]);
      digitButtons[nextBut].addActionListener(listener);
    }
 
    //create a message for the user
    JLabel instruct = new JLabel("Press a button");
 
    //add the components to this JPanel
    setLayout(new BorderLayout());
    add(instruct, BorderLayout.NORTH);
    add(buttonGrid, BorderLayout.CENTER);
    add(display, BorderLayout.SOUTH);  
  }
 
  //represents a listener for button presses 
  private class ButtonListener implements ActionListener{
 
    //what to do when a button has been pressed */
    public void actionPerformed(ActionEvent aE){
 
      JButton whichButton = (JButton) aE.getSource();
      display.setText(  whichButton.getText());
 
      if ("+".equals(whichButton.getText())){
        calc.inOperator("+");
      }else if ("-".equals(whichButton.getText())){
        calc.inOperator("-");
      }else if ("*".equals(whichButton.getText())){
        calc.inOperator("*");
      }else if ("=".equals(whichButton.getText())){
        calc.inEquals();
        display.setText(calc.getResult());
      }else if ("C".equals(whichButton.getText())){
        calc.inClear();
        display.setText("0");
      }else{
        long i = 0;
        Scanner scan = new Scanner(whichButton.getText());
        i = scan.nextLong();
        calc.inDigit(i);
        display.setText(calc.getCurrentInput());
      }
 
    }
  }
 
}

public class Calculator{  
 
  private long currentInput;          //current input
  private long previousInput;         // previous input
  private long result;            // result of calculation
  private String lastOperator = "";  // keeps track of the last operator entered
 
 
  //new digit entered as integer value i - moves currentInput 1 decimal place to the left and adds i in "one's column"
  public void inDigit(long i){
 
    currentInput = (currentInput * 10) + i;
  }
 
  //operator entered  + - or *  
  public void inOperator(String op){
 
    previousInput = currentInput;      // save the new input as previous to get ready for next input
    currentInput = 0;
    lastOperator = op;                 // remember which operator was entered
  } 
 
 
   //equals operation sets result to previousInput + - or * currentInput (depending on lastOperator)
  public void inEquals(){
 
    if (lastOperator.equals("+")){
      result = previousInput + currentInput;     
    } else if (lastOperator.equals("-")) { 
      result = previousInput - currentInput;
    } else if (lastOperator.equals("*"))  {
      result = previousInput * currentInput;
    } 
    lastOperator = "";       // reset last operator to "nothing"
  }
 
  //clear operation
  public void inClear(){
 
    currentInput = 0;
    previousInput = 0;
    result = 0;
    lastOperator = "";
  } 
 
  //returns the current result
  public String getResult(){
 
    return Long.toString(result);  //converts int to String
  }
 
  //returns the previous input value
  public String getPreviousInput(){
 
    return Long.toString(previousInput);
  }
 
  //returns the current input value
  public String getCurrentInput(){
 
    return Long.toString(currentInput);
  }
 
}