設置例外

Question

我無法理解如何在我的任務中執行以下步驟，我想要具有Exception超類構造函數是什麼意思？我會在哪裏把那個

這裏只是EmptyFieldException類

import javax.swing.*; 
import java.awt.*; 
import java.awt.event.*; 

public class EmptyFieldException 

{ 
    EmptyFieldException() 
    { 



    } 


} 

這裏是我的應用程序，其中大部分的工作是做

import javax.swing.*; 
import java.awt.*; 
import java.awt.event.*; 
import javax.swing.border.*; 

public class AccountApplet extends JApplet implements ActionListener 
{  
    // For West 
    public JLabel ai  = new JLabel("Account ID "); 
    public JTextField aitf = new JTextField(); 
    public JLabel ab  = new JLabel("Account Balance "); 
    public JTextField abtf = new JTextField(); 

    // For East 
    public JButton  dp = new JButton ("Deposit"); 
    public JTextField dptf = new JTextField(); 
    public JButton  wt = new JButton ("Withdraw"); 
    public JTextField wttf = new JTextField(); 

    // For South 
    public JLabel status = new JLabel("placeholder"); 


    public void init() 
    { 
    this.setSize(400, 90); 

    //---------------------- 
    // Set up the Structure 
    //---------------------- 

    Container  c = getContentPane(); 
    JPanel   b = new JPanel(new BorderLayout()); 
    JPanel  west = new JPanel(new GridLayout(2,2)); 
    JPanel  east = new JPanel(new BorderLayout()); 
    JPanel depo_with = new JPanel(new GridLayout(2,2)); 



    // Add BorderLayout to the container 
    c.add(b); 

    // Add everything to West 
    b.add(west, BorderLayout.WEST); 


    west.setBorder(new TitledBorder("Display Account Information")); 
    west.add(ai); 
    west.add(aitf); 
    aitf.setEditable(false); 
    west.add(ab); 
    west.add(abtf); 
    abtf.setEditable(false); 

    // Add everything to EAST 
    b.add(east, BorderLayout.EAST); 

    east.setBorder(new TitledBorder("Deposit or Withdrawl Funds")); 

    east.add(depo_with, BorderLayout.EAST); 

    depo_with.add(dptf); 
    depo_with.add(dp); 
    depo_with.add(wttf); 
    depo_with.add(wt); 

    dp.addActionListener(this); 
    wt.addActionListener(this); 

    // Add everything to EAST 
    b.add(status, BorderLayout.SOUTH); 






    } // End intit 

    public void actionPerformed(ActionEvent e) 
    { 
    if (e.getSource() == dp) // Executes if deposit was clicked 
    { 
    }  

    if (e.getSource() == wt) // Executes if withdraw was clicked 
    { 
    } 
    } // End actionPerformed 

    public void refreshFields() 
    { 
    // diplays accound id and balance in left text fields 
    //should be called when the applet is first displayed and after each valid transaction 
    } 

    public double getAmount(JTextField tf) //throws EmptyFieldException, 
             //  NumberFormatException, 
             //  NegativeAmountException 
    { 
    return 5.0; 
    } // End getAmount 


} // End Class 

Answer 1

調用父類的構造函數與super關鍵字完成：

...將消息傳遞給異常超類的構造函數。

public class MyException extends Exception { // Exception is the superclass 

    public MyException() { 
     super("My Message"); // call Exception's constructor 
    } 

} 

父類的構造調用類的構造函數（可能除了Object）時，總是叫。

但是，如果超類構造函數沒有參數，則不必顯式調用super()。

還應該指出，對超類構造函數的調用必須始終是構造函數中的第一條語句。