引发自定义Java异常

Question

I am working on a homework assignment for a Java Data Structures class, and we have to build a program from a stack ADT using a linked list implementation. The professor has requested that we include a method called popTop() which pops the top element of the stack, and throws a "StackUnderflowException" if the stack is empty. From what I can gather this is an exception class that we have to write ourselves, and I am having some problems with it. If anyone could help me I would be extremely appreciative. Here is some of my code:

private class StackUnderflowException extends RuntimeException {

    public StackUnderflowException() {
        super("Cannot pop the top, stack is empty");
    }
    public StackUnderflowException(String message) {
        super(message);
    }
}

That's the exception class I wrote, here is the beginning of the popTop() method that I have written thus far:

public T popTop() throws StackUnderflowException {
    if (sz <= 0) {
        throw new StackUnderflowException();
    }
}

I am getting errors suggesting that StackUnderflowException cannot be a subclass of RuntimeException, could anyone shed some more light on this? And within the method I'm getting errors saying StackUnderflowException is undefined.

Answer 1

您的构造函数是私有的，应该扩展Exception而不是RuntimeException 。

Answer 2

There are 2 problems with your code 1.Your customised Exception class is private 2. It extends runtime exception where it should be entensing the superclass Exception

You can create custom exception as is given below:

public class StackUnderflowException extends Exception{

private static final long serialVersionUID = 1L;

/**
 * Default constructor.
 */
public StackUnderflowException(){

}
/**
 * The constructor wraps the exception thrown in a method.
 * @param e the exception instance.
 */
public StackUnderflowException( Throwable e) 
{
    super(e);
}
/**
 * The constructor wraps the exception and the message thrown in a method.
 * @param msg the exception instance.
 * @param e the exception message.
 */
public StackUnderflowException(String msg, Throwable e) 
{
    super(msg, e);

}

/**
 * The constructor initializes the exception message.
 * @param msg the exception message 
 */
public StackUnderflowException(String msg) 
{
    super(msg);
}