java不能跨类更改JLabel
我有一个涉及一些基本JavaGUI的多类项目。我将使用10个类创建贷款计算器（其中6个是JPanel子类、一个计算类、一个CombinedPanels类、一个LoanCalculatorGUI类，该类创建CombinedPanels类和calculation类的实例，以及一个驱动程序）。我必须在一个JPanel子类（ActionButtons）中创建一个重置按钮，然后在另一个JPanel子类（PaymentInformation）中更改一个私有JLabel。下面是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
}
}
}
}
以及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);
}
}
我试图使用PaymentInformation中的setValue方法来更改JLabel的文本，但单击reset按钮时它保持不变（在“5.0”）。我不确定是否需要这样做，但CombinedPanels类（获取所有JLabel子类并将它们放入JFrame中）如下所示：
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，这里是GUI的一个图像：
即使“5.0”JLabel应更改为“0.0”，当点击重置时，它仍保持不变。但是，“退出”按钮可以正常工作
很抱歉出现了文字墙，但这个问题快把我逼疯了。任何帮助或解释都将不胜感激。提前谢谢
# 1 楼答案
您有3个独立的
PaymentInformation实例。第一个在CombinedPanels类中（显示的那一个），一个在ActionButtons类中，一个在ButtonListener类中。只更改最后一个（不可见）的值因此，一种解决方案是将
CombinedPanels类的（可见的）pi传递给ActionButtons类，并在该实例上调用changeValues()，而不是在其他实例上调用相关代码（已更改）：
# 2 楼答案
试试这个