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这里是我的货币转换程序代码。 先前的空指针异常发生，但已被整理。现在程序中没有错误。程序运行但转换按钮不执行任何操作。我相信问题存在于ActionPerformed函数中，但我无法识别它。JButton没有执行它在java中的必需功能
import java.awt.event.*;
import javax.swing.*;
import java.awt.*;
import java.io.*;
public class Trial extends JFrame implements ActionListener{
public String[] list={"DOLLARS","EUROS ","YEN","POUNDS","RUPEES"};
JPanel panel1 = new JPanel();
JPanel panel2 = new JPanel();
public JComboBox cb,cb1;
public JTextField tf1;
public JTextField tf2;
public JLabel label3;
public JLabel label4;
JPanel panel3 = new JPanel();
public JButton button1;
public JButton button2;
public Trial(){
setLayout(new BoxLayout(getContentPane(),BoxLayout.Y_AXIS));
getContentPane().setLayout(
new BoxLayout(getContentPane(), BoxLayout.PAGE_AXIS)
);
JLabel label1 = new JLabel("FROM :");
label1.setFont(new Font("Serif", Font.BOLD, 15));
JComboBox cb = new JComboBox();
cb= new JComboBox(list);
cb.getSelectedIndex();
panel1.setBackground(Color.RED);
panel1.add(label1);
panel1.add(cb);
JLabel label2 = new JLabel("TO :");
label2.setFont(new Font("Serif", Font.BOLD, 15));
JComboBox cb1 = new JComboBox();
cb1=new JComboBox(list);
cb1.getSelectedIndex();
cb.addActionListener(this);
cb1.addActionListener(this);
panel1.add(label2);
panel1.add(cb1);
add(panel1);
JLabel label3 = new JLabel("\n\nENTER THE AMOUNT :");
label3.setFont(new Font("Serif", Font.BOLD, 15));
JTextField tf1 = new JTextField(15);
// label3.setHorizontalAlignment(SwingConstants.CENTER);
// label3.setVerticalAlignment(SwingConstants.CENTER);
panel2.add(label3);
panel2.add(tf1);
JLabel label4 = new JLabel("CONVERTED AMOUNT :");
label4.setFont(new Font("Serif", Font.BOLD, 15));
label4.setDisplayedMnemonic(KeyEvent.VK_O);
JTextField tf2 = new JTextField(15);
tf1.addActionListener(this);
tf2.addActionListener(this);
panel2.add(label4);
panel2.add(tf2);
panel2.setBackground(Color.BLUE);
add(panel2);
JButton button1 = new JButton("CONVERT");
button1.setFont(new Font("Serif", Font.BOLD, 15));
button1.setMnemonic(KeyEvent.VK_K);
panel3.add(button1);
JButton button2 = new JButton("CLEAR ");
button2.setFont(new Font("Serif", Font.BOLD, 15));
button2.setMnemonic(KeyEvent.VK_C);
button1.addActionListener(this);
button2.addActionListener(this);
panel3.add(button2);
panel3.setBackground(Color.GREEN);
add(panel3);
}
public void actionPerformed(ActionEvent e) {
double a,b=0;
Object src = e.getSource();
if(src.equals(button1)){
a=Double.valueOf(tf1.getText());
try{
if(cb.getSelectedIndex()==0 && cb1.getSelectedIndex()==1)
{b=a*0.89;}
if(cb.getSelectedIndex()==0 && cb1.getSelectedIndex()==2)
{b=a*124.75;}
if(cb.getSelectedIndex()==0 && cb1.getSelectedIndex()==3)
{b=a*0.65;}
if(cb.getSelectedIndex()==0 && cb1.getSelectedIndex()==4)
{b=a*64.08;}
if(cb.getSelectedIndex()==1 && cb1.getSelectedIndex()==0)
{b=a*1.13;}
if(cb.getSelectedIndex()==1 && cb1.getSelectedIndex()==2)
{b=a*140.49;}
if(cb.getSelectedIndex()==1 && cb1.getSelectedIndex()==3)
{b=a*0.74;}
if(cb.getSelectedIndex()==1 && cb1.getSelectedIndex()==4)
{b=a*71.34;}
if(cb.getSelectedIndex()==2 && cb1.getSelectedIndex()==0)
{b=a*0.0080;}
if(cb.getSelectedIndex()==2 && cb1.getSelectedIndex()==1)
{b=a*0.0071;}
if(cb.getSelectedIndex()==2 && cb1.getSelectedIndex()==3)
{b=a*0.0052;}
if(cb.getSelectedIndex()==2 && cb1.getSelectedIndex()==4)
{b=a*0.51;}
if(cb.getSelectedIndex()==3 && cb1.getSelectedIndex()==0)
{b=a*1.53;}
if(cb.getSelectedIndex()==3 && cb1.getSelectedIndex()==1)
{b=a*1.36;}
if(cb.getSelectedIndex()==3 && cb1.getSelectedIndex()==2)
{b=a*191.26;}
if(cb.getSelectedIndex()==3 && cb1.getSelectedIndex()==4)
{b=a*97.88;}
if(cb.getSelectedIndex()==4 && cb1.getSelectedIndex()==0)
{b=a*0.0156;}
if(cb.getSelectedIndex()==4 && cb1.getSelectedIndex()==1)
{ b=a*0.014;}
if(cb.getSelectedIndex()==4 && cb1.getSelectedIndex()==2)
{b=a*1.9607;}
if(cb.getSelectedIndex()==4 && cb1.getSelectedIndex()==3)
{b=a*0.0108;}
tf2.setText(String.valueOf(b));
}catch(Exception x){System.out.println("Error");}
}
if(src.equals(button2)){
tf1.setText("0000");
tf2.setText("0000");
}
}
}
我试着改变你的建议，但发生错误：线程“AWT-EventQueue-0”中的异常java.lang.NullPointerException \t at Trial $ thehandler.actionPerformed（Trial.java:116）Error at line - a = Double.valueOf（tf1.getText（））; –
你也影响变量，'tf1'，'tf2'等... – Reimeus
我已纠正所有这些错误。现在没有空点异常，但它仍然没有执行任何功能。代码在异常条款中执行。 –