Java Error: Unreported exception?

Question

I've got the following method:

public T peek() throws StackEmptyException {
    Node<T> tracker = head; 
    while(tracker.getNext() != null) {
        tracker = tracker.getNext(); 
    }
    return tracker.getItem(); 
}

The problem is that when I try to do something like

int firstOne = stack.peek(); 

I get an unreported exception StackEmptyException and I have no idea what I'm doing wrong at this point. The StackEmptyException has been made in a separate class. Am I suppose to have this class extend that new exception class I made? So confused. Thoughts guys?

Answer 1

Checked exceptions (ie, a class which extends Exception but not RuntimeException or Error) thrown by a method should be handled by this method's caller, recursively so.

Here you have .peek() which throws, say, exception class E (bad name, but this is for illustration). You must do one of the following in a foo() method which calls .peek():

• catch it, or
• throw it again.

That is, either:

// catch
void foo()
{
    try {
        peek();
    } catch (E e) {
       // something
    }
}

or:

// throw
void foo() throws E
{
    peek();
}

You could even rethrow it:

// catch then rethrow
void foo() throws E
{
    try {
        peek();
    } catch (E e) {
        // something, then
        throw e;
    }
}