Question

我有一个涉及一些基本Java GUI的多类项目。我将使用10个类创建一个贷款计算器（其中6个是JPanel子类，一个计算类，一个CombinedPanels类，一个LoanCalculatorGUI类，它创建CombinedPanels类和计算类的实例，以及一个驱动程序）。我必须在其中一个JPanel子类（ActionButtons）中创建一个重置按钮，在另一个JPanel子类（PaymentInformation）中更改一个私有JLabel。这是ActionButtons类：

import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JPanel;


@SuppressWarnings("serial")
public class ActionButtons extends JPanel{
private JButton calc, reset, exit;
private JPanel actionButtons;
public ActionButtons(){
    PaymentInformation pi = new PaymentInformation();
    actionButtons = new JPanel(new GridLayout(1, 3, 20, 20));
    calc = new JButton("Calculate");
    reset = new JButton("Reset");
    exit = new JButton("Exit");
    actionButtons.add(calc);
    actionButtons.add(reset);
    actionButtons.add(exit);
    actionButtons.setBorder(BorderFactory.createTitledBorder("Action Buttons"));

    //Add ActionListeners
    calc.addActionListener(new ButtonListener());
    reset.addActionListener(new ButtonListener());
    exit.addActionListener(new ButtonListener());

}

public JPanel getGUI(){
    return actionButtons;
}



private class ButtonListener implements ActionListener{
    public void actionPerformed(ActionEvent e) {
        PaymentInformation pi = new PaymentInformation();
        if(e.getActionCommand().equals("Exit")){
            System.exit(0);
        }
        if(e.getActionCommand().equals("Reset")){
            pi.changeValues("0.0");
        }
        if(e.getActionCommand().equals("Calculate")){
            //TODO DO CALCULATIONS 
        }

    }

  }
}

还有PaymentInformation类：

import java.awt.GridLayout;

import javax.swing.BorderFactory;
import javax.swing.JLabel;
import javax.swing.JPanel;


 @SuppressWarnings("serial")
 public class PaymentInformation extends JPanel{
//Declare variables
private JPanel payInfo;
private JLabel loanAmt, monthPay, totalPay, loanVal, monthVal, totalVal;

public PaymentInformation(){
    //Give panel layout
    payInfo = new JPanel(new GridLayout(3, 2));
    //Give titles, set alignment
    loanAmt = new JLabel("Total Loan Amount:  $", JLabel.LEFT);
    monthPay = new JLabel("Monthly Payment:  $", JLabel.LEFT);
    totalPay = new JLabel("Total Payment:  $", JLabel.LEFT);
    loanVal = new JLabel("5.0", JLabel.RIGHT);
    monthVal = new JLabel("0.0", JLabel.RIGHT);
    totalVal = new JLabel("0.0", JLabel.RIGHT);
    //Add stuff to JPanel
    payInfo.add(loanAmt);
    payInfo.add(loanVal);
    payInfo.add(monthPay);
    payInfo.add(monthVal);
    payInfo.add(totalPay);
    payInfo.add(totalVal);
    //Set border
    payInfo.setBorder(BorderFactory.createTitledBorder("Payment Information"));
}
//Method to get the JPanel
public JPanel getGUI(){
    return payInfo;
}

public void changeValues(String val){
    loanVal.setText(val);
 }
}

我正在尝试使用PaymentInformation中的setValue方法来更改JLabel的文本，但是当单击重置按钮时它保持不变（在“5.0”处）。我不确定是否需要这个，但CombinedPanels类（获取所有JLabel子类并将它们放入JFrame）在这里：

import java.awt.BorderLayout;
import java.awt.GridLayout;

import javax.swing.JFrame;
import javax.swing.JPanel;


@SuppressWarnings("serial")
public class CombinedPanels extends JFrame{
public CombinedPanels(){
    setTitle("Auto Loan Calculator");
    setSize(700,500);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setLayout(new BorderLayout());
    JPanel center = new JPanel(new GridLayout(2, 2, 20, 20));

    //Add other classes to this layout
    TitleBar tb = new TitleBar();
    add(tb.getGUI(), BorderLayout.NORTH);
    ActionButtons ab = new ActionButtons();
    add(ab.getGUI(), BorderLayout.SOUTH);
    //Add center JPanel to the center of BorderLayout
    add(center, BorderLayout.CENTER);
    //Continue with adding rest of classes to center JPanel
    PaymentInformation pi = new PaymentInformation();
    center.add(pi.getGUI());
    LoanTerm lt = new LoanTerm();
    center.add(lt.getGUI());
    FinancingInformation fi = new FinancingInformation();
    center.add(fi.getGUI());
    PriceWithOptions pwo = new PriceWithOptions();
    center.add(pwo.getGUI());
 }
}

最后，这是GUI的图像：。

当重置命中时，它保持不变，即使“5.0”JLabel应该更改为“0.0”。但是，退出按钮功能正常。

抱歉文字的墙，但这个问题让我发疯。任何帮助或解释都非常感谢。提前谢谢。

Answer 1

您有3个单独的PaymentInformation个实例。 CombinedPanels类中的第一个（显示的那个），ActionButtons类中的一个和ButtonListener类中的一个。您只能更改最后一个的值（不可见）。

因此，一种解决方案是将pi类的（可见）CombinedPanels传递给ActionButtons类，并在上调用changeValues() 实例而不是其他。

相关代码（已更改）：

public CombinedPanels() {
    setTitle("Auto Loan Calculator");
    setSize(700, 500);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setLayout(new BorderLayout());
    JPanel center = new JPanel(new GridLayout(2, 2, 20, 20));

    // Add other classes to this layout
    PaymentInformation pi = new PaymentInformation();
    ActionButtons ab = new ActionButtons(pi);
    add(ab.getGUI(), BorderLayout.SOUTH);
    // Add center JPanel to the center of BorderLayout
    add(center, BorderLayout.CENTER);
    // Continue with adding rest of classes to center JPanel
    center.add(pi.getGUI());
    setVisible(true);
}

public class ActionButtons extends JPanel {
    private JButton calc, reset, exit;
    private JPanel actionButtons;
    PaymentInformation pi;

    public ActionButtons(PaymentInformation pi) {
        this.pi = pi;
        actionButtons = new JPanel(new GridLayout(1, 3, 20, 20));
        calc = new JButton("Calculate");
        reset = new JButton("Reset");
        exit = new JButton("Exit");
        actionButtons.add(calc);
        actionButtons.add(reset);
        actionButtons.add(exit);
        actionButtons.setBorder(BorderFactory.createTitledBorder("Action Buttons"));

        // Add ActionListeners
        calc.addActionListener(new ButtonListener());
        reset.addActionListener(new ButtonListener());
        exit.addActionListener(new ButtonListener());

    }

    public JPanel getGUI() {
        return actionButtons;
    }

    private class ButtonListener implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            if (e.getActionCommand().equals("Exit")) {
                System.exit(0);
            }
            if (e.getActionCommand().equals("Reset")) {
                pi.changeValues("0.0");
            }
            if (e.getActionCommand().equals("Calculate")) {
                // TODO DO CALCULATIONS
            }

        }

    }
}

Answer 2

试试这个

public void changeValues(String val){
    loanVal=new JLabel(val, JLabel.RIGHT);
 }

无法跨类更改JLabel

2 个答案: