我正在尝试进行货币兑换计划,但如果第二个输入(此处为s1)为空,则程序会给出NumberFormatException:Empty String error
。当第一个(此处)为空时它起作用。所以我想知道是否有另一种方法可以通过一个按钮选择它。当第二个字段为空时,为什么它不工作?
public class kanvas1 implements ActionListener,WindowListener{
private JTextField tf;
private JTextField tf1;
private JTextField tf2;
private JTextField tf3;
private JLabel lb;
private JLabel lb1;
private JButton bt;
private JButton bt1;
public kanvas1()
{
tf=new JTextField();
tf1=new JTextField();
tf2=new JTextField();
tf3=new JTextField();
lb=new JLabel("$");
lb1=new JLabel("TL");
bt=new JButton("Cevir");
bt1=new JButton("Sıfırla");
pencere();
}
public void pencere() {
tf.setBounds(50,20,150,50);
tf1.setBounds(50,80, 150, 50);
tf2.setBounds(220,20,150,50);
tf3.setBounds(220,80,150,50);
lb.setBounds(30,20,20, 50);
lb1.setBounds(30,80,20,50);
bt.setBounds(400,20,100, 50);
bt1.setBounds(400,80,100,50);
bt.addActionListener(this);
bt1.addActionListener(this);
JFrame ab=new JFrame();
ab.setVisible(true);
ab.setSize(600,200);
ab.setLayout(null);
ab.add(tf);ab.add(tf1);ab.add(tf2);ab.add(tf3);ab.add(bt);ab.add(bt1);ab.add(lb);ab.add(lb1);
bt.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent arg0) {
String s=tf.getText(); //problem is here
double a=Double.parseDouble(s);
double c=a*5.44;
String result=String.valueOf(c);
tf2.setText(result);
}
});
bt.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent arg0) {
String s1=tf1.getText();
//and here
double b=Double.parseDouble(s1);
double d=b*0.18;
String result1=String.valueOf(d);
tf3.setText(result1);
}
});
bt1.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
tf.setText("");
tf1.setText("");
tf2.setText("");
tf3.setText("");
}
});
}
@Override
public void windowActivated(WindowEvent arg0) {
// TODO Auto-generated method stub
}
@Override
public void windowClosed(WindowEvent arg0) {
// TODO Auto-generated method stub
}
@Override
public void windowClosing(WindowEvent arg0) {
System.exit(0);
}
@Override
public void windowDeactivated(WindowEvent arg0) {
// TODO Auto-generated method stub
}
@Override
public void windowDeiconified(WindowEvent arg0) {
// TODO Auto-generated method stub
}
@Override
public void windowIconified(WindowEvent arg0) {
// TODO Auto-generated method stub
}
@Override
public void windowOpened(WindowEvent arg0) {
// TODO Auto-generated method stub
}
public static void main(String args[]) {
new kanvas1();
}
@Override
public void actionPerformed(ActionEvent arg0) {
// TODO Auto-generated method stub
}
}
您可以在解析之前添加一个检查,如下所示:
if (s1.isEmpty())
return;
它失败了因为Double.parseDouble(String arg)
尝试将作为参数传递的字符串转换为字符串表示的Double。这意味着像“12”,“12.0”等字符串是有效输入,而“12a”,“ac”,“”等字符串必然会失败;因为,毕竟,12a
不是双倍(它甚至不是一个数字!)。
如果文本字段为空并且您执行getText()
,您将检索的是""
(空字符串)而不是null
。
所以,如果你想做出任何有条件的决定,你的条件基于empty i.e. ""
而不是null
检索到的文本
而不是像同一个按钮两次写addActionListener
,你可以在单个addActionListener
中写它。此外,避免保持任何字段为空,你得到NumberFormatException
,因为你的一个JTextField
给出空白值或任何其他不是双倍的值。使用Double.parseDouble(“12.34”)进行解析时,应始终包含字符串格式的double值。解析休息其他值抛出NumberFormatException
bt.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent arg0) {
String s=tf.getText(); //problem is here
double a=Double.parseDouble(s);
double c=a*5.44;
String result=String.valueOf(c);
tf2.setText(result);
}
});
bt.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent arg0) {
String s1=tf1.getText();
//and here
double b=Double.parseDouble(s1);
double d=b*0.18;
String result1=String.valueOf(d);
tf3.setText(result1);
}
});
将以上代码替换为:
bt.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent arg0) {
String s=tf.getText();
double a=Double.parseDouble(s);
double c=a*5.44;
String result=String.valueOf(c);
tf2.setText(result);
String s1=tf1.getText();
double b=Double.parseDouble(s1);
double d=b*0.18;
String result1=String.valueOf(d);
tf3.setText(result1);
}
});