长度转换器

Question

我有一个转换长度的Swing应用程序。英寸到厘米，脚到院子，等等。我想知道我是否能让超大的HashMap变得更小，或者更高效。任何其他建议也将受到赞赏。

import java.awt.*;
import java.awt.event.*;
import java.util.HashMap;
import javax.swing.*;
public class LengthConverter{
    private JFrame frame;
    private JLabel welcomeLabel;
    private JPanel fromPanel;
    private JLabel centerLabel;
    private JTextField fromField;
    private JComboBox<String> fromBox;
    private JPanel toPanel;
    private JTextField toField;
    private JComboBox<String> toBox;
    private JButton submitButton;
    private JLabel noteLabel;
    private JPanel bottomPanel;
    private final String[] lengthTypes = {"Inches", "Centimeters", "Feet", "Yards", "Meters", "Millimeters"};
    private final HashMap<String, HashMap<String, Double>> conversions = new HashMap<>();
    public LengthConverter() {
        conversions.put("Inches", new HashMap<>());

        conversions.get("Inches").put("Inches", 1.0);
        conversions.get("Inches").put("Centimeters", 2.54);
        conversions.get("Inches").put("Feet", 0.0833333);
        conversions.get("Inches").put("Yards", 0.0277778);
        conversions.get("Inches").put("Meters", 0.0254);
        conversions.get("Inches").put("Millimeters", 25.4);

        conversions.put("Centimeters", new HashMap<>());

        conversions.get("Centimeters").put("Inches", 0.393701);
        conversions.get("Centimeters").put("Centimeters", 1.0);
        conversions.get("Centimeters").put("Feet", 0.0328084);
        conversions.get("Centimeters").put("Yards", 0.0109361);
        conversions.get("Centimeters").put("Meters", 0.01);
        conversions.get("Centimeters").put("Millimeters", 10.0);

        conversions.put("Feet", new HashMap<>());

        conversions.get("Feet").put("Inches", 12.0);
        conversions.get("Feet").put("Centimeters", 30.48);
        conversions.get("Feet").put("Feet", 1.0);
        conversions.get("Feet").put("Yards", 0.3333333);
        conversions.get("Feet").put("Meters", 0.3048);
        conversions.get("Feet").put("Millimeters", 304.8);

        conversions.put("Yards", new HashMap<>());

        conversions.get("Yards").put("Inches", 36.0);
        conversions.get("Yards").put("Centimeters", 91.44);
        conversions.get("Yards").put("Feet", 3.0);
        conversions.get("Yards").put("Yards", 1.0);
        conversions.get("Yards").put("Meters", 0.9144);
        conversions.get("Yards").put("Millimeters", 914.4);

        conversions.put("Meters", new HashMap<>());

        conversions.get("Meters").put("Inches", 39.3701);
        conversions.get("Meters").put("Centimeters", 100.0);
        conversions.get("Meters").put("Feet", 3.28084);
        conversions.get("Meters").put("Yards", 1.09361);
        conversions.get("Meters").put("Meters", 1.0);
        conversions.get("Meters").put("Millimeters", 1000.0);

        conversions.put("Millimeters", new HashMap<>());

        conversions.get("Millimeters").put("Inches", 0.0393701);
        conversions.get("Millimeters").put("Centimeters", 0.1);
        conversions.get("Millimeters").put("Feet", 0.00328084);
        conversions.get("Millimeters").put("Yards", 0.00109361);
        conversions.get("Millimeters").put("Meters", 0.001);
        conversions.get("Millimeters").put("Millimeters", 1.0);
    }
    public static void main(String[] args) {
        new LengthConverter().go();
    }
    public void go() {
        frame = new JFrame("Length Conversions");
        fromPanel = new JPanel();
        centerLabel = new JLabel("Is...");
        fromField = new JTextField(10);
        fromBox = new JComboBox<>(lengthTypes);
        toPanel = new JPanel();
        toBox = new JComboBox<>(lengthTypes);
        toField = new JTextField(10);
        toField.setEnabled(false);
        welcomeLabel = new JLabel("Welcome to the length converter!");
        submitButton = new JButton("Convert!");
        noteLabel = new JLabel("Note: Rounds to fit the text field.");
        bottomPanel = new JPanel();
        submitButton.addActionListener(new SubmitListener());

        fromPanel.setLayout(new BoxLayout(fromPanel, BoxLayout.X_AXIS));
        fromPanel.add(fromField);
        fromPanel.add(fromBox);

        toPanel.setLayout(new BoxLayout(toPanel, BoxLayout.X_AXIS));
        toPanel.add(toField);
        toPanel.add(toBox);

        bottomPanel.setLayout(new BoxLayout(bottomPanel, BoxLayout.X_AXIS));
        bottomPanel.add(noteLabel);
        bottomPanel.add(submitButton);

        Font labelFont = new Font("Arial", Font.BOLD, 24);
        welcomeLabel.setFont(labelFont);

        frame.setLayout(new BorderLayout());
        Container window = frame.getContentPane();

        window.add(BorderLayout.NORTH, welcomeLabel);
        window.add(BorderLayout.WEST, fromPanel);
        window.add(BorderLayout.EAST, toPanel);
        window.add(BorderLayout.CENTER, centerLabel);
        window.add(BorderLayout.SOUTH, bottomPanel);

        frame.pack();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }
    class SubmitListener implements ActionListener {

        @Override
        public void actionPerformed(ActionEvent e) {
            Double numToConvert = Double.parseDouble(fromField.getText());
            Double conversionRate = conversions.get(fromBox.getSelectedItem()).get(toBox.getSelectedItem());
            String result = Double.toString(numToConvert * conversionRate);
            int length = result.length();
            if (length > 4) {
                Dimension d = frame.getSize();
                frame.setSize(length + d.width - 16, d.height);
                toField.setColumns(length);
            }
            else {
                toField.setColumns(4);
                frame.pack();
            }
            toField.setText(result);
            frame.revalidate();
        }

    }
}

Answer 1

与包含从每个单元到每个其他单元的转换因子的嵌套散列映射不同，只需将每个单元映射为单个公共单元即可，例如仪表：

HashMap<String, Double> conversions = new HashMap<>();

conversions.put("Centimeters", 0.01);
conversions.put("Inches", 0.0254);
// ...

然后，两个单位之间的转换系数可以简单地计算为

Double conversionRate = conversions.get(fromUnit) / conversions.get(toUnit);

实际上，您根本不需要一个散列映射，您可以将信息存储在两个并行数组中：

private final String[] lengthTypes = { "Inches", "Centimeters", "Feet", "Yards", "Meters", "Millimeters"};
private final double[] conversionFactors = { 0.054, 0.01, 0.3048, 0.9144, 1.0, 0.001 };

然后

double conversionRate = conversionFactors[fromBox.getSelectedIndex()] / conversionFactors[toBox.getSelectedIndex()];

或者，定义

class Unit {
    String name;
    double conversionFactor;

    Unit(String name, double conversionFactor) {
        this.name = name;
        this.conversionFactor = conversionFactor;
    }
}

和可用单位的清单

Unit[] units = {
    new Unit("Centimeters", 0.01),
    new Unit("Inches", 0.0254)
    // ...
};

然后将单元名称和相应的因子定义在一起，如果对单元进行重新排序或重命名，则不太容易出错。然后，组合框将被填充

for (Unit unit : units) {
    fromBox.addItem(unit.name);
    toBox.addItem(unit.name);
}

两个单位之间的换算系数是

double conversionRate = units[fromBox.getSelectedIndex()].conversionFactor / units[toBox.getSelectedIndex()].conversionFactor;

Answer 2

LengthConverter是做什么的？它会显示按钮，对点击做出反应吗？或者转换长度？

这显然违反了分离关注点原则。只需将转换提取到单独的类。

实际上，Martin .S的Unit已经这么做了，您也可以使用枚举(注释来自隆布克，但是应该是显而易见的)。

@RequiredArgsConstructor @Getter
public enum Unit {
    METER(1.0),
    CENTIMETER(0.01),
    INCH(0.0254),
    FURLONG(201.168),
    ...
    ;

    double convertFrom(double amount, Unit unit) {
        return amount * unit.meters / this.meters;
    }

    private final double meters;
}

有一个类似的表情

Unit.INCH.convertFrom(2, Unit.LIGHT_YEAR);

告诉你有多少英寸等于2光年。不需要地图。

枚举的明显缺点是它们不能被扩展，但是对于作者来说，这是没有问题的(无论如何，有用的单元集是相当有限的)。