如何将值从一个JLabel传输到另一个JLabel？
我有这个计算器工作，但是当你点击“完成”按钮时，我无法弄清楚如何将结果resultpane的值输入第一个文本框。
我是Java的新手。 我试过这样做，但我一直都是错误的。
import java.awt.BorderLayout; import java.awt.EventQueue; import java.awt.Font; import java.awt.GridBagConstraints; import java.awt.GridBagLayout; import java.awt.Point; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import java.text.NumberFormat; import javax.swing.AbstractAction; import static javax.swing.Action.NAME; import javax.swing.JButton; import javax.swing.JFrame; import javax.swing.JLabel; import javax.swing.JPanel; import javax.swing.JTextField; import javax.swing.Timer; import javax.swing.UIManager; import javax.swing.UnsupportedLookAndFeelException; public class TestCalculator { public static void main(String[] args) { new TestCalculator(); } public TestCalculator() { EventQueue.invokeLater(new Runnable() { @Override public void run() { try { UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName()); } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) { } ResultPane resultPane = new ResultPane(); JFrame frame = new JFrame("Testing"); frame.setGlassPane(resultPane); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setLayout(new BorderLayout()); frame.add(new CalculatorPane(resultPane)); frame.pack(); frame.setLocationRelativeTo(null); frame.setVisible(true); } }); } public class ResultPane extends JPanel { private JLabel result; private Timer timer; private int xDelta = (Math.random() > 0.5) ? 1 : -1; private int yDelta = (Math.random() > 0.5) ? 1 : -1; ; public ResultPane() { setOpaque(false); setLayout(null); result = new JLabel(); Font font = result.getFont(); font = font.deriveFont(Font.BOLD, 26f); result.setFont(font); add(result); timer = new Timer(40, new ActionListener() { @Override public void actionPerformed(ActionEvent e) { Point point = result.getLocation(); point.x += xDelta; point.y += yDelta; if (point.x getWidth()) { point.x = getWidth() - result.getWidth(); xDelta *= -1; } if (point.y getHeight()) { point.y = getHeight() - result.getHeight(); yDelta *= -1; } result.setLocation(point); repaint(); } }); timer.start(); } public void setResult(Number number) { result.setText("Result: " + NumberFormat.getNumberInstance().format(number)); result.setSize(result.getPreferredSize()); setVisible(true); } } public class CalculatorPane extends JPanel { private final ResultPane resultPane; private final JLabel firstNumberLabel = new JLabel("First Number:"); private final JLabel secondNumberLabel = new JLabel("Second Number:"); private final JTextField firstNumberField = new JTextField(5); private final JTextField secondNumberField = new JTextField(5); public CalculatorPane(ResultPane resultPane) { setLayout(new GridBagLayout()); GridBagConstraints gbc = new GridBagConstraints(); gbc.gridwidth = GridBagConstraints.REMAINDER; this.resultPane = resultPane; JPanel fields = new JPanel(); fields.add(firstNumberLabel); fields.add(firstNumberField); fields.add(secondNumberLabel); fields.add(secondNumberField); add(fields, gbc); JPanel buttons = new JPanel(); buttons.add(new JButton(new AddAction())); buttons.add(new JButton(new SubtractAction())); buttons.add(new JButton(new MultiplyAction())); buttons.add(new JButton(new DivideAction())); buttons.add(new JButton(new ToText1Action())); add(buttons, gbc); } public class AddAction extends AbstractAction { public AddAction() { putValue(NAME, "+"); } @Override public void actionPerformed(ActionEvent e) { try { double num1 = Double.parseDouble(firstNumberField.getText()); double num2 = Double.parseDouble(secondNumberField.getText()); double result = num1 + num2; //num1.setResult(firstNumberField); resultPane.setResult(result); } catch (NumberFormatException exp) { } } } public class SubtractAction extends AbstractAction { public SubtractAction() { putValue(NAME, "-"); } @Override public void actionPerformed(ActionEvent e) { try { double num1 = Double.parseDouble(firstNumberField.getText()); double num2 = Double.parseDouble(secondNumberField.getText()); double result = num1 - num2; resultPane.setResult(result); } catch (NumberFormatException exp) { } } } public class MultiplyAction extends AbstractAction { public MultiplyAction() { putValue(NAME, "x"); } @Override public void actionPerformed(ActionEvent e) { try { double num1 = Double.parseDouble(firstNumberField.getText()); double num2 = Double.parseDouble(secondNumberField.getText()); double result = num1 * num2; resultPane.setResult(result); } catch (NumberFormatException exp) { } } } public class DivideAction extends AbstractAction { public DivideAction() { putValue(NAME, "/"); } @Override public void actionPerformed(ActionEvent e) { try { double num1 = Double.parseDouble(firstNumberField.getText()); double num2 = Double.parseDouble(secondNumberField.getText()); double result = num1 / num2; resultPane.setResult(result); } catch (NumberFormatException exp) { } } } public class ToText1Action extends AbstractAction { public ToText1Action() { putValue(NAME, "Finish"); } @Override public void actionPerformed(ActionEvent e) { try { //i would like to put it here } catch (NumberFormatException exp) { } } } } }
为ResultPane提供一个新的公共方法，允许您从其JLabel中提取文本，如：
public String getResultText() { return result.getText(); }
然后在想要获取该字段的文本时调用它：
public class ToText1Action extends AbstractAction { public ToText1Action() { putValue(NAME, "Finish"); } @Override public void actionPerformed(ActionEvent e) { String resultText = resultPane.getResultText(); double number = // extract number from resultText firstNumberField.setText(number); } }
更好的是，只需将最新的结果值存储在一个double变量中，该变量是类的实例字段，例如名为lastResult并使用它设置firstNumberField。
请注意，您不应该有空的catch块。
编辑
例如：
public class CalculatorPane extends JPanel { private final ResultPane resultPane; private final JLabel firstNumberLabel = new JLabel("First Number:"); private final JLabel secondNumberLabel = new JLabel("Second Number:"); private final JTextField firstNumberField = new JTextField(5); private final JTextField secondNumberField = new JTextField(5); private double result = 0.0; // ****** declared here // ***** etc..... ***** public class DivideAction extends AbstractAction { public DivideAction() { putValue(NAME, "/"); } @Override public void actionPerformed(ActionEvent e) { try { double num1 = Double.parseDouble(firstNumberField.getText()); double num2 = Double.parseDouble(secondNumberField.getText()); result = num1 / num2; // ****** note variable not declared resultPane.setResult(result); } catch (NumberFormatException exp) { // show error message // set text fields to "0" } } } public class ToText1Action extends AbstractAction { public ToText1Action() { super("Finish"); putValue(MNEMONIC_KEY, KeyEvent.VK_F); } @Override public void actionPerformed(ActionEvent e) { firstNumberField.setText(String.format("%.2f", result)); } }
作为另一种方法，您可以建立某种模型，这些模型在操作和组件之间共享，这有助于分离UI，因为它的主要链接因素是模型，而不是其他UI元素。
对于ToText1Action ，您还需要将它传递给您想要更新的字段，但由于它主要是一个JTextField ，因此它不应该是坏的……
因此，主要的变化是包含某种模型，它提供了设置结果，获得结果并在模型更改时提供事件通知的方法，因此这些感兴趣的各方可以根据需要自行更新，例如……
public interface ResultsModel { public void setResult(double value); public double getResult(); public void addChangeListener(ChangeListener listener); public void removeChangeListener(ChangeListener listener); } public class DefaultResultsModel implements ResultsModel { private List changeListeners; private double result; public DefaultResultsModel() { changeListeners = new ArrayList<>(25); } public double getResult() { return result; } public void setResult(double value) { if (value != result) { this.result = value; fireStateChanged(); } } protected void fireStateChanged() { if (!changeListeners.isEmpty()) { ChangeEvent evt = new ChangeEvent(this); for (ChangeListener listener : changeListeners) { listener.stateChanged(evt); } } } @Override public void addChangeListener(ChangeListener listener) { changeListeners.add(listener); } @Override public void removeChangeListener(ChangeListener listener) { changeListeners.remove(listener); } }
需要更改ResultsPane和每个操作，以便它们可以使用模型而不是直接使用每个模型。 这意味着ResultsPane现在将侦听模型中的更改，而不是直接更新
import java.awt.BorderLayout; import java.awt.EventQueue; import java.awt.Font; import java.awt.GridBagConstraints; import java.awt.GridBagLayout; import java.awt.Point; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import java.text.NumberFormat; import java.util.ArrayList; import java.util.List; import javax.swing.AbstractAction; import static javax.swing.Action.NAME; import javax.swing.JButton; import javax.swing.JFrame; import javax.swing.JLabel; import javax.swing.JPanel; import javax.swing.JTextField; import javax.swing.Timer; import javax.swing.UIManager; import javax.swing.UnsupportedLookAndFeelException; import javax.swing.event.ChangeEvent; import javax.swing.event.ChangeListener; public class TestCalculator { public static void main(String[] args) { new TestCalculator(); } public TestCalculator() { EventQueue.invokeLater(new Runnable() { @Override public void run() { try { UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName()); } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) { } ResultsModel model = new DefaultResultsModel(); ResultPane resultPane = new ResultPane(); resultPane.setModel(model); JFrame frame = new JFrame("Testing"); frame.setGlassPane(resultPane); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setLayout(new BorderLayout()); frame.add(new CalculatorPane(model)); frame.pack(); frame.setLocationRelativeTo(null); frame.setVisible(true); } }); } public interface ResultsModel { public void setResult(double value); public double getResult(); public void addChangeListener(ChangeListener listener); public void removeChangeListener(ChangeListener listener); } public class DefaultResultsModel implements ResultsModel { private List changeListeners; private double result; public DefaultResultsModel() { changeListeners = new ArrayList<>(25); } @Override public double getResult() { return result; } @Override public void setResult(double value) { if (value != result) { this.result = value; fireStateChanged(); } } protected void fireStateChanged() { if (!changeListeners.isEmpty()) { ChangeEvent evt = new ChangeEvent(this); for (ChangeListener listener : changeListeners) { listener.stateChanged(evt); } } } @Override public void addChangeListener(ChangeListener listener) { changeListeners.add(listener); } @Override public void removeChangeListener(ChangeListener listener) { changeListeners.remove(listener); } } public class ResultPane extends JPanel implements ChangeListener { private ResultsModel model; private JLabel result; private Timer timer; private int xDelta = (Math.random() > 0.5) ? 1 : -1; private int yDelta = (Math.random() > 0.5) ? 1 : -1; public ResultPane() { setOpaque(false); setLayout(null); result = new JLabel(); Font font = result.getFont(); font = font.deriveFont(Font.BOLD, 26f); result.setFont(font); add(result); timer = new Timer(40, new ActionListener() { @Override public void actionPerformed(ActionEvent e) { Point point = result.getLocation(); point.x += xDelta; point.y += yDelta; if (point.x < 0) { point.x = 0; xDelta *= -1; } else if (point.x + result.getWidth() > getWidth()) { point.x = getWidth() - result.getWidth(); xDelta *= -1; } if (point.y < 0) { point.y = 0; yDelta *= -1; } else if (point.y + result.getHeight() > getHeight()) { point.y = getHeight() - result.getHeight(); yDelta *= -1; } result.setLocation(point); repaint(); } }); timer.start(); } public void setModel(ResultsModel value) { if (value != model) { if (model != null) { model.removeChangeListener(this); } model = value; if (model != null) { model.addChangeListener(this); } } } public ResultsModel getModel() { return model; } @Override public void stateChanged(ChangeEvent e) { double number = getModel().getResult(); result.setText("Result: " + NumberFormat.getNumberInstance().format(number)); result.setSize(result.getPreferredSize()); setVisible(true); } } public class CalculatorPane extends JPanel { private final JLabel firstNumberLabel = new JLabel("First Number:"); private final JLabel secondNumberLabel = new JLabel("Second Number:"); private final JTextField firstNumberField = new JTextField(5); private final JTextField secondNumberField = new JTextField(5); public CalculatorPane(ResultsModel model) { setLayout(new GridBagLayout()); GridBagConstraints gbc = new GridBagConstraints(); gbc.gridwidth = GridBagConstraints.REMAINDER; JPanel fields = new JPanel(); fields.add(firstNumberLabel); fields.add(firstNumberField); fields.add(secondNumberLabel); fields.add(secondNumberField); add(fields, gbc); JPanel buttons = new JPanel(); buttons.add(new JButton(new AddAction(model))); buttons.add(new JButton(new SubtractAction(model))); buttons.add(new JButton(new MultiplyAction(model))); buttons.add(new JButton(new DivideAction(model))); buttons.add(new JButton(new ToText1Action(firstNumberField, model))); add(buttons, gbc); } public abstract class AbstractResultsAction extends AbstractAction { private ResultsModel model; public AbstractResultsAction(ResultsModel model) { this.model = model; } public ResultsModel getModel() { return model; } } public class AddAction extends AbstractResultsAction { public AddAction(ResultsModel model) { super(model); putValue(NAME, "+"); } @Override public void actionPerformed(ActionEvent e) { try { double num1 = Double.parseDouble(firstNumberField.getText()); double num2 = Double.parseDouble(secondNumberField.getText()); double result = num1 + num2; //num1.setResult(firstNumberField); getModel().setResult(result); } catch (NumberFormatException exp) { } } } public class SubtractAction extends AbstractResultsAction { public SubtractAction(ResultsModel model) { super(model); putValue(NAME, "-"); } @Override public void actionPerformed(ActionEvent e) { try { double num1 = Double.parseDouble(firstNumberField.getText()); double num2 = Double.parseDouble(secondNumberField.getText()); double result = num1 - num2; getModel().setResult(result); } catch (NumberFormatException exp) { } } } public class MultiplyAction extends AbstractResultsAction { public MultiplyAction(ResultsModel model) { super(model); putValue(NAME, "x"); } @Override public void actionPerformed(ActionEvent e) { try { double num1 = Double.parseDouble(firstNumberField.getText()); double num2 = Double.parseDouble(secondNumberField.getText()); double result = num1 * num2; getModel().setResult(result); } catch (NumberFormatException exp) { } } } public class DivideAction extends AbstractResultsAction { public DivideAction(ResultsModel model) { super(model); putValue(NAME, "/"); } @Override public void actionPerformed(ActionEvent e) { try { double num1 = Double.parseDouble(firstNumberField.getText()); double num2 = Double.parseDouble(secondNumberField.getText()); double result = num1 / num2; getModel().setResult(result); } catch (NumberFormatException exp) { } } } public class ToText1Action extends AbstractResultsAction { private JTextField field; public ToText1Action(JTextField field, ResultsModel model) { super(model); putValue(NAME, "Finish"); this.field = field; } public JTextField getField() { return field; } @Override public void actionPerformed(ActionEvent e) { try { double result = getModel().getResult(); getField().setText(NumberFormat.getNumberInstance().format(result)); //i would like to put it here } catch (NumberFormatException exp) { } } } } }
这是观察者模式的一个例子