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我有一个基本问题。我真的不擅长编程。我试图在我的答案字段中显示小数点后 2 位的答案。我有我的 JTextFields 和我的 JRadioBtn 集。当答案针对我的面积或周长时，会有很多小数位。我只需要它来四舍五入小数点后 2 位。这是我到目前为止的代码：

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import static java.lang.Math.*;

public class Triangle extends JFrame
{
private GridBagLayout layout = new GridBagLayout();
private GridBagConstraints constraints = new GridBagConstraints();
JTextField firstNumberTxt, secondNumberTxt, thirdNumberTxt, answerTxt;
JRadioButton addBtn, subBtn, multBtn, divBtn;
JButton calculateBtn, exitBtn;

public ExamQuestion2()
{
    super( "A Simple Calculator Form." );
    firstNumberTxt = new JTextField( 5 );
    secondNumberTxt = new JTextField( 5 );
    answerTxt = new JTextField( 5 );
    addBtn = new JRadioButton( "area", true );
    subBtn = new JRadioButton( "perimeter", false );

    calculateBtn = new JButton( "cal" +
                "calculate" );
    exitBtn = new JButton( "exit" );

    JLabel firstNumberLbl = new JLabel( "Base: "),
            operationLbl = new JLabel( "Operation "),
            secondNumberLbl = new JLabel( "Height: "),
            answerLbl =new JLabel( "Answer: ");

    setLayout( layout );
    addComponent( firstNumberLbl, 0, 0, 1, 1, GridBagConstraints.EAST );
    addComponent( firstNumberTxt, 0, 1, 1, 1, GridBagConstraints.WEST );
    addComponent( operationLbl, 1, 0, 1, 4, GridBagConstraints.CENTER );
    addComponent( addBtn, 1, 1, 1, 1, GridBagConstraints.WEST );
    addComponent( subBtn, 2, 1, 1, 1, GridBagConstraints.WEST );
    addComponent( secondNumberLbl, 5, 0, 1, 1, GridBagConstraints.EAST );
    addComponent( secondNumberTxt, 5, 1, 1, 1, GridBagConstraints.WEST );
    addComponent( answerLbl, 6, 0, 1, 1, GridBagConstraints.EAST );
    addComponent( answerTxt, 6, 1, 1, 1, GridBagConstraints.WEST );
    addComponent( calculateBtn, 7, 0, 1, 1, GridBagConstraints.EAST );
    addComponent( exitBtn, 7, 1, 1, 1, GridBagConstraints.WEST );

    calculateBtn.addActionListener( new Calculator() );
    exitBtn.addActionListener( new Exiter() );
}

private void addComponent( Component component, int row, int column, int width, int height, int anch )
{
    constraints.gridx = column;
    constraints.gridy = row;
    constraints.gridwidth = width;
    constraints.gridheight = height;
    constraints.anchor = anch;
    constraints.weighty = 5;
    add( component );
    layout.setConstraints( component, constraints );
}

private class Calculator implements ActionListener
{
    public void actionPerformed( ActionEvent event )
    {
        String firstString, secondString;
        int choice;
        int firstNumber, secondNumber;

        firstString = firstNumberTxt.getText();
        secondString = secondNumberTxt.getText();
        if( firstString.length() < 1 || secondString.length() < 1)
        {
            answerTxt.setText( " INVALID" );
            return;
        }
        firstNumber = Integer.parseInt( firstString );
        secondNumber = Integer.parseInt( secondString );

        if( addBtn.isSelected() )
        {
            choice = 0;
            subBtn.setSelected( false );
        }
        if( addBtn.isSelected() ) choice = 0;
        else if( subBtn.isSelected() ) choice = 1;
        else if( multBtn.isSelected() ) choice = 2;
        else choice = 3;

        switch ( choice )
        {
        case 0: answerTxt.setText( ( (firstNumber * secondNumber) / 2 ) +     "" ); break;
        case 1: answerTxt.setText( ( firstNumber + secondNumber + sqrt(     (firstNumber * firstNumber) + 
                (secondNumber * secondNumber))) + "" ); break;
        default: if ( secondNumber != 0 )
                {
                    answerTxt.setText( ( firstNumber /     secondNumber ) + "" ); break;
                }
        else answerTxt.setText( " INVALID " ); break;

        }
    }
}

public static void main(String[] args) 
{
    Triangle MyCalculator= new Triangle();
    MyCalculator.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
    MyCalculator.setSize( 300, 300 );
    MyCalculator.setLocationRelativeTo(null);
    MyCalculator.setVisible( true );
}

private class Exiter implements ActionListener
{
    public void actionPerformed( ActionEvent event)
    {
        System.exit(0);
    }
}
}

我已经查看并尝试了一些我在网上找到的东西，但似乎无法让任何东西正常工作。有人帮忙吗？

4

3 回答 3

4

试试NumberFormat.getCurrencyInstance()；这里有一个相关的例子。

于 2012-12-18T01:33:13.480 回答
2

尝试使用：

String.format("%.2f", numberToBeRounded);

例如，您可以将包含的行替换为case 0：

case 0: answerTxt.setText( String.format("%.2f", (firstNumber * secondNumber) / 2 ) ); break;

格式说明符将显示一个四舍五入到小数点后两位的%.2f浮点数。有关格式化字符串的更多详细信息，请参阅Formatter文档。

于 2012-12-18T01:27:24.900 回答
1

除了NumberFormat显示您的数字之外，我建议您从代码中退后一步，并查看BigDecimal该类以满足您的数字计算需求。您可以设置比例BigDecimal(BigInteger unscaledVal, int scale)并有效（正确读取）执行数字计算。

于 2012-12-18T01:40:29.423 回答