* A Queue implementation that extends this class must minimally define a method {@link Queue#offer} which does * not permit insertion of null elements, along with methods {@link Queue#peek}, {@link Queue#poll}, * {@link Collection#size}, and {@link Collection#iterator}. Typically, additional methods will be overridden as well. * If these requirements cannot be met, consider instead subclassing {@link AbstractCollection}. * *
* This class is a member of the Java Collections
* Framework.
*
* @since 1.5
* @author Doug Lea
* @param
* This implementation returns true if offer succeeds, else throws an
* IllegalStateException.
*
* @param e
* the element to add
* @return true (as specified by {@link Collection#add})
* @throws IllegalStateException
* if the element cannot be added at this time due to capacity restrictions
* @throws ClassCastException
* if the class of the specified element prevents it from being added to this queue
* @throws NullPointerException
* if the specified element is null and this queue does not permit null elements
* @throws IllegalArgumentException
* if some property of this element prevents it from being added to this queue
*/
@Override
public boolean add(E e) {
if (offer(e)) {
return true;
} else {
throw new IllegalStateException("Queue full");
}
}
/**
* Retrieves and removes the head of this queue. This method differs from {@link #poll poll} only in that it throws
* an exception if this queue is empty.
*
*
* This implementation returns the result of poll unless the queue is empty.
*
* @return the head of this queue
* @throws NoSuchElementException
* if this queue is empty
*/
@Override
public E remove() {
E x = poll();
if (x != null) {
return x;
} else {
throw new NoSuchElementException();
}
}
/**
* Retrieves, but does not remove, the head of this queue. This method differs from {@link #peek peek} only in that
* it throws an exception if this queue is empty.
*
*
* This implementation returns the result of peek unless the queue is empty.
*
* @return the head of this queue
* @throws NoSuchElementException
* if this queue is empty
*/
@Override
public E element() {
E x = peek();
if (x != null) {
return x;
} else {
throw new NoSuchElementException();
}
}
/**
* Removes all of the elements from this queue. The queue will be empty after this call returns.
*
*
* This implementation repeatedly invokes {@link #poll poll} until it returns null.
*/
@Override
public void clear() {
while (poll() != null) {
;
}
}
/**
* Adds all of the elements in the specified collection to this queue. Attempts to addAll of a queue to itself
* result in IllegalArgumentException. Further, the behavior of this operation is undefined if the
* specified collection is modified while the operation is in progress.
*
*
* This implementation iterates over the specified collection, and adds each element returned by the iterator to
* this queue, in turn. A runtime exception encountered while trying to add an element (including, in particular, a
* null element) may result in only some of the elements having been successfully added when the associated
* exception is thrown.
*
* @param c
* collection containing elements to be added to this queue
* @return true if this queue changed as a result of the call
* @throws ClassCastException
* if the class of an element of the specified collection prevents it from being added to this queue
* @throws NullPointerException
* if the specified collection contains a null element and this queue does not permit null elements, or
* if the specified collection is null
* @throws IllegalArgumentException
* if some property of an element of the specified collection prevents it from being added to this
* queue, or if the specified collection is this queue
* @throws IllegalStateException
* if not all the elements can be added at this time due to insertion restrictions
* @see #add(Object)
*/
@Override
public boolean addAll(Collection c) {
if (c == null) {
throw new NullPointerException();
}
if (c == this) {
throw new IllegalArgumentException();
}
boolean modified = false;
for (E e : c) {
if (add(e)) {
modified = true;
}
}
return modified;
}
}