Java postfix calculator push/pop method with a String[] array

Question

I have created a new class that references a postfix calculator. This uses the push() and pop() methods. Here is the code (Updated from comments below using a String Builder()):

import java.util.Stack;
import java.util.*;
import java.io.*;


public class StackCalculation 
{
public static void main (String[] args) throws Exception
{
    String[] str = {"22+"};
    String string = convertStringArrayToString(str);
    System.out.println(string);
    Stack<String> stack = new Stack<String>();
    stack.add(string);
    double a = 0;
    double b = 0;
    double sum = 0;
    while (!stack.isEmpty())
    {
        if(stack.peek().equals("+"))
        {
            a = Double.parseDouble(stack.peek());
            stack.pop();
            b = Double.parseDouble(stack.peek());
            stack.pop();
            sum = a + b;
            //Write something to push back the sum of the last 2 numbers a + b
            stack.push("" + sum);
        }

        else if(stack.peek().equals("*"))
        {
            a = Double.parseDouble(stack.peek());
            stack.pop();
            b = Double.parseDouble(stack.peek());
            stack.pop();
            sum = a * b;
            //Write something to push back the product of the last 2 numbers a * b
            stack.push("" + sum);
        }

        else if(stack.peek().equals("-"))
        {
            a = Double.parseDouble(stack.peek());
            stack.pop();
            b = Double.parseDouble(stack.peek());
            stack.pop();
            sum = a - b;
            //Write something to push back the difference of the last 2 numbers a - b
            stack.push("" + sum);
        }

        else if(stack.peek().equals("/"))
        {
            a = Double.parseDouble(stack.peek());
            stack.pop();
            b = Double.parseDouble(stack.peek());
            stack.pop();
            sum = a / b;
            //Write something to push back the quotient of the last 2 numbers a/b
            stack.push("" + sum);
        }

        else 
        {
            //Convert the last item in the stack to a double and push
            //this into the stack
            String elem = stack.peek();
            a = Double.parseDouble(elem);
            stack.push("" + a);
        }

    }

    System.out.println(stack);
    //System.out.println(string);
}

private static String convertStringArrayToString(String[] strArr) {
    StringBuilder sb = new StringBuilder();
    for(String str : strArr) sb.append(str);
    return sb.toString();
}

}

When I run the code, it returns this error message:

    Exception in thread "main" java.lang.NumberFormatException: For input string: "22+"
        at sun.misc.FloatingDecimal.readJavaFormatString(Unknown Source)
        at java.lang.Double.parseDouble(Unknown Source)
        at StackCalculation.main(StackCalculation.java:69)

It points to:

        else 
        {
            //Convert the last item in the stack to a double and push
            //this into the stack
            String elem = stack.peek();
            a = Double.parseDouble(elem);
            stack.push("" + a);
        }

I tried passing through a String Builder method to convert the string array into a string.

The logic behind postfix calculation is as follows:

read in a symbol (number or operator)
As long as you’re not at the end of the entire string yet
if the symbol is +
    pop the last 2 values from the stack
    push back their sum
else if the symbol is *
    pop the last 2 values from the stack and
    push back their product
else if the symbol is –
    pop the last 2 values from the stack and
    push back the difference (second value – first value)
else if the symbol is /
    pop the last 2 values from the stack
    push back the quotient (second value / first value)
else if symbol is =
    print the top of the stack
    pop the stack
else if the symbol is a number
    convert to a double and push it on the stack; read the next symbol, 
    repeat above steps and do until you’re at the end of the string

The full program is pasted below, I am creating a GUI postfix calculator. I had to use the split() method in String to return the correct getText() output.

I have pasted the original code for the GUI operation below. I am making a new class to test the results of the following method-

// Use the String's split method to get rid of spaces
public String[] getStringOutput()
{
    String str = calculatorLabel.getText();
    String[] string = str.split(" ");

    return string;
}

I am referencing this method inside the calcButtonListener() class which needs to do the postfix calculation when the "Calculate" button is clicked.I don't know of any any way to write the private class calcButtonListener() at the very end.

import javax.swing.*;
import javax.swing.border.Border;

import java.util.Arrays;
import java.util.Stack;
import java.awt.*;
import java.awt.event.*;

public class PostfixCalculator extends JFrame
{
private JPanel calculatedResultPanel;
private JPanel northPanel;
private JPanel centerPanel;
private JPanel southPanel;
private JPanel num1Panel;
private JPanel num2Panel;
private JPanel num3Panel;
private JPanel num4Panel;
private JPanel num5Panel;
private JPanel num6Panel;
private JPanel num7Panel;
private JPanel num8Panel;
private JPanel num9Panel;
private JPanel addPanel;
private JPanel subtractPanel;
private JPanel multiplyPanel;
private JPanel dividePanel;
private JPanel zeroPanel;
private JPanel spacePanel;
private JPanel calculatePanel;
private JPanel clearPanel;
private JButton zero;
private JButton one;
private JButton two;
private JButton three;
private JButton four;
private JButton five;
private JButton six;
private JButton seven;
private JButton eight;
private JButton nine;
private JButton add;
private JButton subtract;
private JButton multiply;
private JButton divide;
private JButton space;
private JButton calculate;
private JButton clear;
private JLabel calculatorLabel;
private final int WINDOW_WIDTH = 350;
private final int WINDOW_HEIGHT = 250;

// Main
public static void main(String[] args)
{
    new PostfixCalculator();
}

// Constructor
public PostfixCalculator()
{
    setTitle("Posfix Calculator");
    setSize(WINDOW_WIDTH, WINDOW_HEIGHT);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    // Build the panel and add it to the frame
    buildPanel();

    //Get the string output from the buttons pressed
    getStringOutput();

    // Display the window
    setVisible(true);
}

// The buildPanel method is created to add a label, text field,
// and a button to the panel
public void buildPanel()
{
    // Use the insert containers method
    insertContainers();

    // Adjust the north panel to display the label bar
    Border border = BorderFactory.createLineBorder(Color.BLACK, 1);
    calculatorLabel.setBorder(border);
    calculatorLabel.setPreferredSize(new Dimension(150, 25));
    calculatedResultPanel.add(calculatorLabel);
    northPanel.add(calculatedResultPanel);
    add(northPanel, BorderLayout.NORTH);

    // Adjust the east panel to display the majority
    // of the buttons
    centerPanel.setLayout(new GridLayout(4,4));
    num1Panel.add(one);
    num2Panel.add(two);
    num3Panel.add(three);
    addPanel.add(add);
    num4Panel.add(four);
    num5Panel.add(five);
    num6Panel.add(six);
    subtractPanel.add(subtract);
    num7Panel.add(seven);
    num8Panel.add(eight);
    num9Panel.add(nine);
    multiplyPanel.add(multiply);
    zeroPanel.add(zero);
    clearPanel.add(clear);
    dividePanel.add(divide);
    centerPanel.add(num1Panel);
    centerPanel.add(num2Panel);
    centerPanel.add(num3Panel);
    centerPanel.add(addPanel);
    centerPanel.add(num4Panel);
    centerPanel.add(num5Panel);
    centerPanel.add(num6Panel);
    centerPanel.add(subtractPanel);
    centerPanel.add(num7Panel);
    centerPanel.add(num8Panel);
    centerPanel.add(num9Panel);
    centerPanel.add(multiplyPanel);
    centerPanel.add(Box.createRigidArea(new Dimension(0,5)));
    centerPanel.add(zeroPanel);
    centerPanel.add(clearPanel);
    centerPanel.add(dividePanel);
    add(centerPanel, BorderLayout.CENTER);

    // Put the remaining buttons and labels inside the South panel
    southPanel.setLayout(new GridLayout(1,3));
    calculatePanel.add(calculate);
    spacePanel.add(space);
    southPanel.add(Box.createRigidArea(new Dimension(0,5)));
    southPanel.add(calculatePanel);
    southPanel.add(spacePanel);
    add(southPanel, BorderLayout.SOUTH);

    // Add the action listeners to the panel
    zero.addActionListener(new buttonListener());
    one.addActionListener(new buttonListener());
    two.addActionListener(new buttonListener());
    three.addActionListener(new buttonListener());
    four.addActionListener(new buttonListener());
    five.addActionListener(new buttonListener());
    six.addActionListener(new buttonListener());
    seven.addActionListener(new buttonListener());
    eight.addActionListener(new buttonListener());
    nine.addActionListener(new buttonListener());
    add.addActionListener(new buttonListener());
    subtract.addActionListener(new buttonListener());
    multiply.addActionListener(new buttonListener());
    divide.addActionListener(new buttonListener());
    space.addActionListener(new buttonListener());
    clear.addActionListener(new buttonListener());

    //Add the action listener for the calculate button
    calculate.addActionListener(new buttonListener());
}

// Insert the panels, buttons and labels into the frame
public void insertContainers()
{
    // Insert a label for the calculator output
    calculatorLabel = new JLabel("");

    // Create the panels
    calculatedResultPanel = new JPanel();
    northPanel = new JPanel();
    centerPanel = new JPanel();
    southPanel = new JPanel();

    // Create the specialized panels

    num1Panel = new JPanel();
    num2Panel = new JPanel();
    num3Panel = new JPanel();
    num4Panel = new JPanel();
    num5Panel = new JPanel();
    num6Panel = new JPanel();
    num7Panel = new JPanel();
    num8Panel = new JPanel();
    num9Panel = new JPanel();
    addPanel = new JPanel();
    subtractPanel = new JPanel();
    multiplyPanel = new JPanel();
    zeroPanel = new JPanel();
    clearPanel = new JPanel();
    dividePanel = new JPanel();
    calculatePanel = new JPanel();
    spacePanel = new JPanel();

    // Create the buttons to be displayed
    one = new JButton("1");
    two = new JButton("2");
    three = new JButton("3");
    four = new JButton("4");
    five = new JButton("5");
    six = new JButton("6");
    seven = new JButton("7");
    eight = new JButton("8");
    nine = new JButton("9");
    add = new JButton("+");
    subtract = new JButton("-");
    multiply = new JButton("*");
    zero = new JButton("0");
    clear = new JButton("C");
    divide = new JButton("/");
    calculate = new JButton("Calculate");
    space = new JButton("_");
}

// Use the String's split method to get rid of spaces
public String[] getStringOutput()
{
    String str = calculatorLabel.getText();
    String[] string = str.split(" ");

    return string;
}

// Needed to convert the getStringOutput() method above from a String[] to a String.
private static String convertStringArrayToString(String[] strArr) {
    StringBuilder sb = new StringBuilder();
    for(String str : strArr) sb.append(str);
    return sb.toString();
}

// Add the button pressed to the JLabel field
private class buttonListener implements ActionListener
{
    public void actionPerformed(ActionEvent e)
    {
        // Determine which button was clicked and add this to the JLabel
        if( e.getSource() == zero)
            calculatorLabel.setText(calculatorLabel.getText() + "0");

        if( e.getSource() == one)
            calculatorLabel.setText(calculatorLabel.getText() + "1");

        if( e.getSource() == two)
            calculatorLabel.setText(calculatorLabel.getText() + "2");

        if( e.getSource() == three)
            calculatorLabel.setText(calculatorLabel.getText() + "3");

        if( e.getSource() == four)
            calculatorLabel.setText(calculatorLabel.getText() + "4");

        if( e.getSource() == five)
            calculatorLabel.setText(calculatorLabel.getText() + "5");

        if( e.getSource() == six)
            calculatorLabel.setText(calculatorLabel.getText() + "6");

        if( e.getSource() == seven)
            calculatorLabel.setText(calculatorLabel.getText() + "7");

        if( e.getSource() == eight)
            calculatorLabel.setText(calculatorLabel.getText() + "8");

        if( e.getSource() == nine)
            calculatorLabel.setText(calculatorLabel.getText() + "9");

        if( e.getSource() == add)
            calculatorLabel.setText(calculatorLabel.getText() + "+");

        if( e.getSource() == subtract)
            calculatorLabel.setText(calculatorLabel.getText() + "-");

        if( e.getSource() == multiply)
            calculatorLabel.setText(calculatorLabel.getText() + "*");

        if( e.getSource() == divide)
            calculatorLabel.setText(calculatorLabel.getText() + "/");

        if( e.getSource() == space)
            calculatorLabel.setText(calculatorLabel.getText() + " ");

        if( e.getSource() == clear)
            calculatorLabel.setText("");
    }

    // Create the calculator button action listener.

    // Add the button pressed to the JLabel field
    private class calcButtonListener implements ActionListener
    {
        public void actionPerformed(ActionEvent e)
        {
            String[] str = getStringOutput();
            String string = convertStringArrayToString(str);
            Stack<String> stack = new Stack<String>();
            stack.add(string);
            double a = 0;
            double b = 0;
            double sum = 0;
            while (!stack.isEmpty())
            {
                if(stack.peek().equals("+"))
                {
                    a = Double.parseDouble(stack.peek());
                    stack.pop();
                    b = Double.parseDouble(stack.peek());
                    stack.pop();
                    sum = a + b;
                    //Write something to push back the sum of the last 2 numbers a + b
                    stack.push("" + sum);
                }

                else if(stack.peek().equals("*"))
                {
                    a = Double.parseDouble(stack.peek());
                    stack.pop();
                    b = Double.parseDouble(stack.peek());
                    stack.pop();
                    sum = a * b;
                    //Write something to push back the product of the last 2 numbers a * b
                    stack.push("" + sum);
                }

                else if(stack.peek().equals("-"))
                {
                    a = Double.parseDouble(stack.peek());
                    stack.pop();
                    b = Double.parseDouble(stack.peek());
                    stack.pop();
                    sum = a - b;
                    //Write something to push back the difference of the last 2 numbers a - b
                    stack.push("" + sum);
                }

                else if(stack.peek().equals("/"))
                {
                    a = Double.parseDouble(stack.peek());
                    stack.pop();
                    b = Double.parseDouble(stack.peek());
                    stack.pop();
                    sum = a / b;
                    //Write something to push back the quotient of the last 2 numbers a/b
                    stack.push("" + sum);
                }

                else 
                {
                    //Convert the last item in the stack to a double and push
                    //this into the stack
                    String elem = stack.peek();
                    a = Double.parseDouble(elem);
                    stack.push("" + a);
                }

            }
        }
    }
}

}

Thank You, how could I adjust the method so that it reads "+" first instead of "22+"? Why does a = Integer.parseInt(stack.peek()) return "22+" instead of "+"? — Axion004, Jul 13 '14 at 17:41
@Zoe: Flagging this question as a duplicate isn't helpful to the OP. This question was answered 5 years ago, I don't see any reason to downvote it 5 years later. — Axion004, Aug 24 '19 at 15:43
@Axion004 [pop] is being burninated. That means old off-topic/duplicate questions will be closed and eventually deleted, along with the tag. See https://meta.stackoverflow.com/q/261320/6296561 — Zoe, Aug 24 '19 at 15:48

Federico Piazza · Accepted Answer · 2014-07-14T00:08:19.303

2

You are storing the string "22+" in String[] str = {"22+"}; and then you are trying to use it as number in a = Integer.parseInt(stack.peek());

So, if you want to use that notation, you will have to parse your stack.peek() result.

If you know that peek() will return 22+ so you can do:

stack.peek().split("\\+")[0]

Btw, the java.lang.NumberFormatException: For input string: "[22+]" is exactly that, you are trying to convert a number using the invalid string 22+ for an integer. The line which return this error is: Integer.parseInt(stack.peek());

A debugger can help you to find this issue and you can see it easily by dividing:

a = Integer.parseInt(stack.peek());

Into:

String elem = stack.peek();
a = Integer.parseInt(elem);

edited Jul 14 '14 at 00:08

answered Jul 13 '14 at 17:52

Federico Piazza

30,085
15
87
123

Thanks, I found what I was doing wrong. I need to adjust the program to this- – Axion004 Jul 14 '14 at 11:54
@user3752432 good to hear that. Glad to help you :) – Federico Piazza Jul 14 '14 at 16:05

Java postfix calculator push/pop method with a String[] array

1 Answers1

Linked