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POAlgorithm and Hint for Scientific Calculator
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copied!<p>I have a Scientific Calculator project using Java Swing. but, I ended up in wrong calculation. Example: If push button:</p> <p>1 then + then 2 then * then 3 the answer is 9, not 7.</p> <p>Could you give me a hint, I must use what classes? And how about the algorithm to make it right answer?</p> <p>Thank you</p> <pre><code>class Calculator{ public static void main(String[] args){ EventQueue.invokeLater(new Runnable(){ public void run(){ CalculatorFrame frame = new CalculatorFrame(); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setVisible(true); } } ); } } class CalculatorFrame extends JFrame{ public CalculatorFrame(){ setTitle("Calculator"); CalculatorPanel panel = new CalculatorPanel(); add(panel); pack(); } } class CalculatorPanel extends JPanel{ public CalculatorPanel(){ setLayout(new BorderLayout()); result = 0; lastCommand = "="; start = true; // add the display display = new JButton(""); display.setEnabled(false); add(display, BorderLayout.NORTH); ActionListener insert = new InsertAction(); ActionListener command = new CommandAction(); // add the buttons in a x grid panel = new JPanel(); panel.setLayout(new GridLayout(4,4 )); addButton("7", insert); addButton("8", insert); addButton("9", insert); addButton("/", command); addButton("4", insert); addButton("5", insert); addButton("6", insert); addButton("*", command); addButton("1", insert); addButton("2", insert); addButton("3", insert); addButton("-", command); addButton("0", insert); addButton(".", insert); addButton("=", command); addButton("+", command); add(panel, BorderLayout.CENTER); } private void addButton(String label, ActionListener listener){ JButton button = new JButton(label); button.addActionListener(listener); panel.add(button); } private class InsertAction implements ActionListener{ public void actionPerformed(ActionEvent event){ String input = event.getActionCommand(); if (start){ display.setText(""); start = false; } display.setText(display.getText() + input); } } private class CommandAction implements ActionListener{ public void actionPerformed(ActionEvent event) { String command = event.getActionCommand(); if (start){ if (command.equals("-")){ display.setText(command); start = false; } else lastCommand = command; } else{ calculate(Double.parseDouble(display.getText())); lastCommand = command; start = true; } } } public void calculate(double x){ if (lastCommand.equals("+")) result += x; else if (lastCommand.equals("-")) result -= x; else if (lastCommand.equals("*")) result *= x; else if (lastCommand.equals("/")) result /= x; else if (lastCommand.equals("=")) result = x; display.setText("" + result); } private JButton display; private JPanel panel; private double result; private String lastCommand; private boolean start; } </code></pre>

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