科学计算器的算法和提示 [英] Algorithm and Hint for Scientific Calculator

问题描述

我有一个使用Java Swing的科学计算器项目。但是，我最终得出了错误的计算结果。示例：如果按钮：

I have a Scientific Calculator project using Java Swing. but, I ended up in wrong calculation. Example: If push button:

1然后+然后2然后*然后3然后答案是9，而不是7。

1 then + then 2 then * then 3 the answer is 9, not 7.

能否给我一个提示，我必须使用什么类？

Could you give me a hint, I must use what classes? And how about the algorithm to make it right answer?

谢谢

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;
}

推荐答案

您还可以使用一些数学任务，并在JavaScript引擎中使用它来进行计算。更多信息此处。

You can also create String with some mathematical task and use it in JavaScript engine to calculate it. More info here.

// create a script engine manager
ScriptEngineManager factory = new ScriptEngineManager();
// create a JavaScript engine
ScriptEngine engine = factory.getEngineByName("JavaScript");

Double d=(Double)engine.eval("1 + 2 * 3");
System.out.println(d);

输出 7.0

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