Question

我正在为我的CS类编写一个程序，它应该是一个带有加/减/乘/除功能的简单计算器。在显示文本时，我希望它看起来尽可能类似于Windows计算器，一个方形显示窗口，文本右下方对齐。单击运算符时，它应显示在第二行，然后是缩进，然后是第二个数字。插入数字和一切的代码工作正常。显示代码不是。我读到我应该使用HTML在标签中创建换行符，这给了我下面的代码：

private void display()
   {
     if (!(firstEntry == ""))
        jDisplay.setText("<html>" + firstEntry + "</html>");
     if (!(oper == ""))
        jDisplay.setText("<html>" + jDisplay.getText() + "<br/>" + oper + "</html>");   
     if (!(secondEntry == ""))
        jDisplay.setText("<html>" + jDisplay.getText() + "  " + secondEntry + "</html>");         
   }

第一个数字显示正常，但是一旦我点击一个操作符，一切都会消失。我做错了什么？

Answer 1

我的建议是为这个特殊需求创建一个新组件。这里有一个示例代码。

import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import java.awt.event.ActionEvent;

import javax.swing.AbstractAction;
import javax.swing.BorderFactory;
import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.KeyStroke;
import javax.swing.SwingConstants;


public class Calculator {

JPanel calcPanel;
Display display;

String[] operators={"+", "-", "*", "/", "="};
double currentValue=0;
String currentOperator="=";

public Calculator() {
    initCalc();
}

private void initCalc() {
    display=new Display();

    int xPos=0;
    int yPos=0;

    calcPanel=new JPanel();
    calcPanel.setLayout(new GridBagLayout());
    calcPanel.add(display, new GridBagConstraints(xPos, yPos, 3, 1, 1.0, 1.0, GridBagConstraints.CENTER, GridBagConstraints.BOTH, new Insets(5, 5, 5, 5), 0, 0));

    for(int i=0;i<=9;i++)
    {
        KeyStroke keyStroke=KeyStroke.getKeyStroke(i, 0);
        AbstractAction action=new AbstractAction() {
            @Override
            public void actionPerformed(ActionEvent e) {
                String value=display.getValue()+((Button) e.getSource()).getText();
                display.setValue(value);
            }
        };

        Button b=new Button(keyStroke, action, Integer.toString(i));

        if(i%3==0)
        {
            xPos=0;
            yPos++;
        }
        else
        {
            xPos++;
        }

        calcPanel.add(b, new GridBagConstraints(xPos, yPos, 1, 1, 1.0, 1.0, GridBagConstraints.CENTER, GridBagConstraints.BOTH, new Insets(5, 5, 5, 5), 0, 0));
    }

    for(String s:operators)
    {
        KeyStroke keyStroke=KeyStroke.getKeyStroke(s);
        AbstractAction action=new AbstractAction() {
            @Override
            public void actionPerformed(ActionEvent e) {
                if(currentOperator.equals("="))
                {
                    display.clearDisplay();
                }
                String value=display.getValue();

                if(e.getActionCommand().equals("="))
                    display.appendDisplay(value );
                else
                    display.appendDisplay(value + " " +e.getActionCommand());

                if(e.getActionCommand()=="=")
                {
                    double dValue=Double.parseDouble(value);;

                    if(currentOperator.equals("+"))
                    {
                        currentValue+=dValue;
                    }
                    else if(currentOperator.equals("-"))
                    {
                        currentValue-=dValue;
                    }
                    else if(currentOperator.equals("*"))
                    {
                        currentValue*=dValue;
                    }
                    else if(currentOperator.equals("/"))
                    {
                        currentValue/=dValue;
                    }
                    display.setValue(Double.toString(currentValue));

                }
                else
                {
                    currentValue=Double.parseDouble(value);
                    display.setValue(" ");  

                }
                currentOperator=e.getActionCommand();

            }
        };

        Button b=new Button(keyStroke, action, s);



        calcPanel.add(b, new GridBagConstraints(xPos, yPos, 1, 1, 1.0, 1.0, GridBagConstraints.CENTER, GridBagConstraints.BOTH, new Insets(5, 5, 5, 5), 0, 0));

        xPos++;
        if(xPos%3==0)
        {
            xPos=0;
            yPos++;

        }
    }

}


public void showCalc()
{
    JFrame f=new JFrame();
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    f.setContentPane(calcPanel);
    f.pack();
    f.setVisible(true);
}


public static void main(String[] args)
{
    Calculator calc=new Calculator();
    calc.showCalc();
}

class Display extends JComponent
{
    JLabel displayLabel=new JLabel(" ");

    JLabel valueLabel=new JLabel(" ");

    String displayString;

    public Display() {
        super();
        setLayout(new BoxLayout(this, BoxLayout.Y_AXIS));
        add(displayLabel);
        add(valueLabel);
        setBorder(BorderFactory.createEtchedBorder());

        displayLabel.setHorizontalAlignment(SwingConstants.RIGHT);
        displayLabel.setHorizontalTextPosition(SwingConstants.RIGHT);
        valueLabel.setHorizontalAlignment(SwingConstants.RIGHT);
        valueLabel.setHorizontalTextPosition(SwingConstants.RIGHT);

    }

    public String getValue()
    {
        return valueLabel.getText();
    }

    public void setValue(String value)
    {
        valueLabel.setText(value);
    }

    public void appendDisplay(String value)
    {
        displayString=(displayString=="" || displayString==null)? value: (displayString) + "<br/>" + value ;
        displayLabel.setText("<html>" + displayString+"</html>");
    }

    public void clearDisplay()
    {
        displayString=" ";
        displayLabel.setText(displayString);
    }
}

class Button extends JButton
{
    public Button(KeyStroke keyStroke, AbstractAction action, String actionCommand) {
        super(action);
        setActionCommand(actionCommand);
        setText(actionCommand);
        getInputMap().put(keyStroke, "action");
    }
}
}

Java计算器中的多行标签

1 个答案: