Question

我正在尝试编写一个自定义异常，在使用GUI和jtextfield输入数据时找到空字段。这是我第一次真正处理异常并编写异常，所以我不确定该怎么做。下面的代码是我迄今为止能够弄清楚的，它不起作用。我的问题是，任何人都有任何指针或进展可以指出我正确的方向来完成这个。

import javax.swing.*;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.LinkedList;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JTextField;

public class PersonFrame extends JFrame {

/**
 * 
 */
private static final long serialVersionUID = 1L;
static LinkedList<Person> listOfObjects = new LinkedList<Person>(); 
JTextField fName;
JTextField lName;
JTextField Height;


public PersonFrame()
{
    setTitle("Person");
    setSize(200, 130);
    setLocationRelativeTo(null);
    setLayout(new GridLayout(4,2));
    add(new JLabel("First Name"));
    fName = new JTextField();
    add(fName);
    add(new JLabel("Last Name"));
    lName = new JTextField();
    add(lName);
    add(new JLabel("Height"));
    Height = new JTextField();
    add(Height);
    JButton jbtSubmit = new JButton("Submit");
    JButton jbtCancel = new JButton("Cancel");
    add(jbtSubmit);
    add(jbtCancel);
    SubmitListenerClass listener1 = new SubmitListenerClass();
    CancelListenerClass listener2 = new CancelListenerClass();
    jbtSubmit.addActionListener(listener1);
    jbtCancel.addActionListener(listener2);
    setVisible(true);

}

public void CloseWindow()
{
    this.setVisible(false);
}
public Person SubmitData()
{
    String fn = fName.getText();
    String ln = lName.getText();
    String h = Height.getText();
    int h1 = 0; 
    if(!(h.equals(""))){
    h1 = Integer.parseInt(Height.getText());    
    }   
    Person p = new Person(fn, ln, h1);
    int i = OneMissingFieldException(p);
    if(i == 1);
    System.out.println(p);

    return p;
    }


public void OutputList() throws IOException
{
    if(listOfObjects.peekFirst()!=null)
    {
        PrintWriter pw = new PrintWriter( new FileWriter("outputp.txt") );
        Object[] pa = listOfObjects.toArray();
        pw.println("Person");
        for(int x = 0; x<pa.length; x++)
        {
            pw.println(pa[x]);
            pw.println("");
        }
        pw.close();
    }
 }

class CancelListenerClass implements ActionListener {
  public void actionPerformed(ActionEvent e) {
    CloseWindow();
  }
}
 class SubmitListenerClass implements ActionListener {
  public void actionPerformed(ActionEvent e) {


      listOfObjects.add(SubmitData());
    CloseWindow();

}
}

public int OneMissingFieldException(Person p) extends Exception
{
    System.out.println("one");
    String fName = ((Person) p).getFName();
    String lName = ((Person) p).getFName(); 
    int height = ((Person) p).getHeight();  
    try 
    {
        System.out.println("two");
    if(fName == "" || fName == null || fName == " ");
        throw new MissingFieldException();

    }
    catch(MissingFieldException mfe){
        System.out.println("You did not enter a first name.");
        return 0;
    }

    try 
    {
    if(lName == "" || lName == null || lName == " ")

        throw new MissingFieldException();          
    }
    catch(MissingFieldException mfe){
        System.out.println("You did not enter a last name." + mfe);
        return 0;
    }

    try 
    {

    if(height ==  0 )

        throw new MissingFieldException();
    }
    catch(MissingFieldException mfe){
        System.out.println("You did not enter a height." + mfe);
    return 0;
    }

return 1;

}

经过一段时间的努力，这就是我所拥有的。只是想知道我是否朝着正确的方向前进。

public Person SubmitData()
{
    Person p = null;
    try{
    String fn = fName.getText();
    String ln = lName.getText();
    String h = Height.getText();
    int h1 = 0; 
    if(!(h.equals(""))){
    h1 = Integer.parseInt(Height.getText());    
    p = new Person(fn, ln, h1);
    checkForMissingFields(p);
    }   

    }
    catch(MissingFieldException e){
    }


    System.out.println(p);

    return p;
    }

  public class MissingFieldException extends Exception {

/**
 * 
 */
private static final long serialVersionUID = 1L;

/**
 * @param args
 */
public static void main(String args){}
public MissingFieldException() { } 
public MissingFieldException( String msg ) {
      super( msg );
 }
public void checkForMissingFields( Object o ) throws MissingFieldException {
int i =OneMissingFieldException(o);
if(i == 1)
    throw new MissingFieldException();

 }


public static int OneMissingFieldException(Object o)
{
    if (o instanceof Person)
{
        String fName = ((Person) o).getFName();
        String lName = ((Person) o).getFName(); 
        int height = ((Person) o).getHeight();


        if(fName == "" || fName == null || fName == " "){
            System.out.println("You did not enter a first name.");  
            return 1;
        }


        if(lName == "" || lName == null || lName == " "){
            System.out.println("You did not enter a last name.");
            return 1;
        }

        if(height == 0)     {       
            System.out.println("You did not enter a height.");
            return 1;           
        }
        return 0;
}
        }
}

Answer 1

您在下面的行中混淆了方法和类。

public int OneMissingFieldException(Person p) extends Exception
{ ... }

您需要两种不同的结构。

这是一个基本的自定义异常类：

public static class MissingFieldException extends Exception {
     public MissingFieldException() { } 
     public MissingFieldException( String msg ) {
          super( msg );
     }
}

这是一个可以抛出异常的方法：

 public void checkForMissingFields( Person p ) throws MissingFieldException {
      ...
 }

您可以在不检查返回值的情况下调用此方法。 的例外情况。您可以检测何时使用catch块抛出异常。

public Person submitData() { Person p = null; try { p = ...; checkForMissingFields( p ); ... } catch ( MissingFieldException e) { // handle exception } return p; }

java自定义异常首先尝试

1 个答案: