java.util.AbstractList Maven / Gradle / Ivy
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package java.util;
/**
* This class provides a skeletal implementation of the {@link List}
* interface to minimize the effort required to implement this interface
* backed by a "random access" data store (such as an array). For sequential
* access data (such as a linked list), {@link AbstractSequentialList} should
* be used in preference to this class.
*
* To implement an unmodifiable list, the programmer needs only to extend
* this class and provide implementations for the {@link #get(int)} and
* {@link List#size() size()} methods.
*
*
To implement a modifiable list, the programmer must additionally
* override the {@link #set(int, Object) set(int, E)} method (which otherwise
* throws an {@code UnsupportedOperationException}). If the list is
* variable-size the programmer must additionally override the
* {@link #add(int, Object) add(int, E)} and {@link #remove(int)} methods.
*
*
The programmer should generally provide a void (no argument) and collection
* constructor, as per the recommendation in the {@link Collection} interface
* specification.
*
*
Unlike the other abstract collection implementations, the programmer does
* not have to provide an iterator implementation; the iterator and
* list iterator are implemented by this class, on top of the "random access"
* methods:
* {@link #get(int)},
* {@link #set(int, Object) set(int, E)},
* {@link #add(int, Object) add(int, E)} and
* {@link #remove(int)}.
*
*
The documentation for each non-abstract method in this class describes its
* implementation in detail. Each of these methods may be overridden if the
* collection being implemented admits a more efficient implementation.
*
*
This class is a member of the
*
* Java Collections Framework.
*
* @author Josh Bloch
* @author Neal Gafter
* @since 1.2
*/
public abstract class AbstractList extends AbstractCollection implements List {
/**
* Sole constructor. (For invocation by subclass constructors, typically
* implicit.)
*/
protected AbstractList() {
}
/**
* Appends the specified element to the end of this list (optional
* operation).
*
* Lists that support this operation may place limitations on what
* elements may be added to this list. In particular, some
* lists will refuse to add null elements, and others will impose
* restrictions on the type of elements that may be added. List
* classes should clearly specify in their documentation any restrictions
* on what elements may be added.
*
*
This implementation calls {@code add(size(), e)}.
*
*
Note that this implementation throws an
* {@code UnsupportedOperationException} unless
* {@link #add(int, Object) add(int, E)} is overridden.
*
* @param e element to be appended to this list
* @return {@code true} (as specified by {@link Collection#add})
* @throws UnsupportedOperationException if the {@code add} operation
* is not supported by this list
* @throws ClassCastException if the class of the specified element
* prevents it from being added to this list
* @throws NullPointerException if the specified element is null and this
* list does not permit null elements
* @throws IllegalArgumentException if some property of this element
* prevents it from being added to this list
*/
public boolean add(E e) {
add(size(), e);
return true;
}
/**
* {@inheritDoc}
*
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
abstract public E get(int index);
/**
* {@inheritDoc}
*
*
This implementation always throws an
* {@code UnsupportedOperationException}.
*
* @throws UnsupportedOperationException {@inheritDoc}
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
* @throws IllegalArgumentException {@inheritDoc}
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public E set(int index, E element) {
throw new UnsupportedOperationException();
}
/**
* {@inheritDoc}
*
*
This implementation always throws an
* {@code UnsupportedOperationException}.
*
* @throws UnsupportedOperationException {@inheritDoc}
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
* @throws IllegalArgumentException {@inheritDoc}
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public void add(int index, E element) {
throw new UnsupportedOperationException();
}
/**
* {@inheritDoc}
*
*
This implementation always throws an
* {@code UnsupportedOperationException}.
*
* @throws UnsupportedOperationException {@inheritDoc}
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public E remove(int index) {
throw new UnsupportedOperationException();
}
// Search Operations
/**
* {@inheritDoc}
*
*
This implementation first gets a list iterator (with
* {@code listIterator()}). Then, it iterates over the list until the
* specified element is found or the end of the list is reached.
*
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
*/
public int indexOf(Object o) {
ListIterator it = listIterator();
if (o==null) {
while (it.hasNext())
if (it.next()==null)
return it.previousIndex();
} else {
while (it.hasNext())
if (o.equals(it.next()))
return it.previousIndex();
}
return -1;
}
/**
* {@inheritDoc}
*
* This implementation first gets a list iterator that points to the end
* of the list (with {@code listIterator(size())}). Then, it iterates
* backwards over the list until the specified element is found, or the
* beginning of the list is reached.
*
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
*/
public int lastIndexOf(Object o) {
ListIterator it = listIterator(size());
if (o==null) {
while (it.hasPrevious())
if (it.previous()==null)
return it.nextIndex();
} else {
while (it.hasPrevious())
if (o.equals(it.previous()))
return it.nextIndex();
}
return -1;
}
// Bulk Operations
/**
* Removes all of the elements from this list (optional operation).
* The list will be empty after this call returns.
*
* This implementation calls {@code removeRange(0, size())}.
*
*
Note that this implementation throws an
* {@code UnsupportedOperationException} unless {@code remove(int
* index)} or {@code removeRange(int fromIndex, int toIndex)} is
* overridden.
*
* @throws UnsupportedOperationException if the {@code clear} operation
* is not supported by this list
*/
public void clear() {
removeRange(0, size());
}
/**
* {@inheritDoc}
*
*
This implementation gets an iterator over the specified collection
* and iterates over it, inserting the elements obtained from the
* iterator into this list at the appropriate position, one at a time,
* using {@code add(int, E)}.
* Many implementations will override this method for efficiency.
*
*
Note that this implementation throws an
* {@code UnsupportedOperationException} unless
* {@link #add(int, Object) add(int, E)} is overridden.
*
* @throws UnsupportedOperationException {@inheritDoc}
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
* @throws IllegalArgumentException {@inheritDoc}
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public boolean addAll(int index, Collection c) {
rangeCheckForAdd(index);
boolean modified = false;
for (E e : c) {
add(index++, e);
modified = true;
}
return modified;
}
// Iterators
/**
* Returns an iterator over the elements in this list in proper sequence.
*
*
This implementation returns a straightforward implementation of the
* iterator interface, relying on the backing list's {@code size()},
* {@code get(int)}, and {@code remove(int)} methods.
*
*
Note that the iterator returned by this method will throw an
* {@link UnsupportedOperationException} in response to its
* {@code remove} method unless the list's {@code remove(int)} method is
* overridden.
*
*
This implementation can be made to throw runtime exceptions in the
* face of concurrent modification, as described in the specification
* for the (protected) {@link #modCount} field.
*
* @return an iterator over the elements in this list in proper sequence
*/
public Iterator iterator() {
return new Itr();
}
/**
* {@inheritDoc}
*
* This implementation returns {@code listIterator(0)}.
*
* @see #listIterator(int)
*/
public ListIterator listIterator() {
return listIterator(0);
}
/**
* {@inheritDoc}
*
* This implementation returns a straightforward implementation of the
* {@code ListIterator} interface that extends the implementation of the
* {@code Iterator} interface returned by the {@code iterator()} method.
* The {@code ListIterator} implementation relies on the backing list's
* {@code get(int)}, {@code set(int, E)}, {@code add(int, E)}
* and {@code remove(int)} methods.
*
*
Note that the list iterator returned by this implementation will
* throw an {@link UnsupportedOperationException} in response to its
* {@code remove}, {@code set} and {@code add} methods unless the
* list's {@code remove(int)}, {@code set(int, E)}, and
* {@code add(int, E)} methods are overridden.
*
*
This implementation can be made to throw runtime exceptions in the
* face of concurrent modification, as described in the specification for
* the (protected) {@link #modCount} field.
*
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public ListIterator listIterator(final int index) {
rangeCheckForAdd(index);
return new ListItr(index);
}
private class Itr implements Iterator {
/**
* Index of element to be returned by subsequent call to next.
*/
int cursor = 0;
/**
* Index of element returned by most recent call to next or
* previous. Reset to -1 if this element is deleted by a call
* to remove.
*/
int lastRet = -1;
/**
* The modCount value that the iterator believes that the backing
* List should have. If this expectation is violated, the iterator
* has detected concurrent modification.
*/
int expectedModCount = modCount;
public boolean hasNext() {
return cursor != size();
}
public E next() {
checkForComodification();
try {
int i = cursor;
E next = get(i);
lastRet = i;
cursor = i + 1;
return next;
} catch (IndexOutOfBoundsException e) {
checkForComodification();
throw new NoSuchElementException();
}
}
public void remove() {
if (lastRet < 0)
throw new IllegalStateException();
checkForComodification();
try {
AbstractList.this.remove(lastRet);
if (lastRet < cursor)
cursor--;
lastRet = -1;
expectedModCount = modCount;
} catch (IndexOutOfBoundsException e) {
throw new ConcurrentModificationException();
}
}
final void checkForComodification() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
}
}
private class ListItr extends Itr implements ListIterator {
ListItr(int index) {
cursor = index;
}
public boolean hasPrevious() {
return cursor != 0;
}
public E previous() {
checkForComodification();
try {
int i = cursor - 1;
E previous = get(i);
lastRet = cursor = i;
return previous;
} catch (IndexOutOfBoundsException e) {
checkForComodification();
throw new NoSuchElementException();
}
}
public int nextIndex() {
return cursor;
}
public int previousIndex() {
return cursor-1;
}
public void set(E e) {
if (lastRet < 0)
throw new IllegalStateException();
checkForComodification();
try {
AbstractList.this.set(lastRet, e);
expectedModCount = modCount;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
public void add(E e) {
checkForComodification();
try {
int i = cursor;
AbstractList.this.add(i, e);
lastRet = -1;
cursor = i + 1;
expectedModCount = modCount;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
}
/**
* {@inheritDoc}
*
* This implementation returns a list that subclasses
* {@code AbstractList}. The subclass stores, in private fields, the
* offset of the subList within the backing list, the size of the subList
* (which can change over its lifetime), and the expected
* {@code modCount} value of the backing list. There are two variants
* of the subclass, one of which implements {@code RandomAccess}.
* If this list implements {@code RandomAccess} the returned list will
* be an instance of the subclass that implements {@code RandomAccess}.
*
*
The subclass's {@code set(int, E)}, {@code get(int)},
* {@code add(int, E)}, {@code remove(int)}, {@code addAll(int,
* Collection)} and {@code removeRange(int, int)} methods all
* delegate to the corresponding methods on the backing abstract list,
* after bounds-checking the index and adjusting for the offset. The
* {@code addAll(Collection c)} method merely returns {@code addAll(size,
* c)}.
*
*
The {@code listIterator(int)} method returns a "wrapper object"
* over a list iterator on the backing list, which is created with the
* corresponding method on the backing list. The {@code iterator} method
* merely returns {@code listIterator()}, and the {@code size} method
* merely returns the subclass's {@code size} field.
*
*
All methods first check to see if the actual {@code modCount} of
* the backing list is equal to its expected value, and throw a
* {@code ConcurrentModificationException} if it is not.
*
* @throws IndexOutOfBoundsException if an endpoint index value is out of range
* {@code (fromIndex < 0 || toIndex > size)}
* @throws IllegalArgumentException if the endpoint indices are out of order
* {@code (fromIndex > toIndex)}
*/
public List subList(int fromIndex, int toIndex) {
return (this instanceof RandomAccess ?
new RandomAccessSubList<>(this, fromIndex, toIndex) :
new SubList<>(this, fromIndex, toIndex));
}
// Comparison and hashing
/**
* Compares the specified object with this list for equality. Returns
* {@code true} if and only if the specified object is also a list, both
* lists have the same size, and all corresponding pairs of elements in
* the two lists are equal. (Two elements {@code e1} and
* {@code e2} are equal if {@code (e1==null ? e2==null :
* e1.equals(e2))}.) In other words, two lists are defined to be
* equal if they contain the same elements in the same order.
*
* This implementation first checks if the specified object is this
* list. If so, it returns {@code true}; if not, it checks if the
* specified object is a list. If not, it returns {@code false}; if so,
* it iterates over both lists, comparing corresponding pairs of elements.
* If any comparison returns {@code false}, this method returns
* {@code false}. If either iterator runs out of elements before the
* other it returns {@code false} (as the lists are of unequal length);
* otherwise it returns {@code true} when the iterations complete.
*
* @param o the object to be compared for equality with this list
* @return {@code true} if the specified object is equal to this list
*/
public boolean equals(Object o) {
if (o == this)
return true;
if (!(o instanceof List))
return false;
ListIterator e1 = listIterator();
ListIterator e2 = ((List) o).listIterator();
while (e1.hasNext() && e2.hasNext()) {
E o1 = e1.next();
Object o2 = e2.next();
if (!(o1==null ? o2==null : o1.equals(o2)))
return false;
}
return !(e1.hasNext() || e2.hasNext());
}
/**
* Returns the hash code value for this list.
*
* This implementation uses exactly the code that is used to define the
* list hash function in the documentation for the {@link List#hashCode}
* method.
*
* @return the hash code value for this list
*/
public int hashCode() {
int hashCode = 1;
for (E e : this)
hashCode = 31*hashCode + (e==null ? 0 : e.hashCode());
return hashCode;
}
/**
* Removes from this list all of the elements whose index is between
* {@code fromIndex}, inclusive, and {@code toIndex}, exclusive.
* Shifts any succeeding elements to the left (reduces their index).
* This call shortens the list by {@code (toIndex - fromIndex)} elements.
* (If {@code toIndex==fromIndex}, this operation has no effect.)
*
*
This method is called by the {@code clear} operation on this list
* and its subLists. Overriding this method to take advantage of
* the internals of the list implementation can substantially
* improve the performance of the {@code clear} operation on this list
* and its subLists.
*
*
This implementation gets a list iterator positioned before
* {@code fromIndex}, and repeatedly calls {@code ListIterator.next}
* followed by {@code ListIterator.remove} until the entire range has
* been removed. Note: if {@code ListIterator.remove} requires linear
* time, this implementation requires quadratic time.
*
* @param fromIndex index of first element to be removed
* @param toIndex index after last element to be removed
*/
protected void removeRange(int fromIndex, int toIndex) {
ListIterator it = listIterator(fromIndex);
for (int i=0, n=toIndex-fromIndex; istructurally modified.
* Structural modifications are those that change the size of the
* list, or otherwise perturb it in such a fashion that iterations in
* progress may yield incorrect results.
*
* This field is used by the iterator and list iterator implementation
* returned by the {@code iterator} and {@code listIterator} methods.
* If the value of this field changes unexpectedly, the iterator (or list
* iterator) will throw a {@code ConcurrentModificationException} in
* response to the {@code next}, {@code remove}, {@code previous},
* {@code set} or {@code add} operations. This provides
* fail-fast behavior, rather than non-deterministic behavior in
* the face of concurrent modification during iteration.
*
*
Use of this field by subclasses is optional. If a subclass
* wishes to provide fail-fast iterators (and list iterators), then it
* merely has to increment this field in its {@code add(int, E)} and
* {@code remove(int)} methods (and any other methods that it overrides
* that result in structural modifications to the list). A single call to
* {@code add(int, E)} or {@code remove(int)} must add no more than
* one to this field, or the iterators (and list iterators) will throw
* bogus {@code ConcurrentModificationExceptions}. If an implementation
* does not wish to provide fail-fast iterators, this field may be
* ignored.
*/
protected transient int modCount = 0;
private void rangeCheckForAdd(int index) {
if (index < 0 || index > size())
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
private String outOfBoundsMsg(int index) {
return "Index: "+index+", Size: "+size();
}
}
class SubList extends AbstractList {
private final AbstractList l;
private final int offset;
private int size;
SubList(AbstractList list, int fromIndex, int toIndex) {
if (fromIndex < 0)
throw new IndexOutOfBoundsException("fromIndex = " + fromIndex);
if (toIndex > list.size())
throw new IndexOutOfBoundsException("toIndex = " + toIndex);
if (fromIndex > toIndex)
throw new IllegalArgumentException("fromIndex(" + fromIndex +
") > toIndex(" + toIndex + ")");
l = list;
offset = fromIndex;
size = toIndex - fromIndex;
this.modCount = l.modCount;
}
public E set(int index, E element) {
rangeCheck(index);
checkForComodification();
return l.set(index+offset, element);
}
public E get(int index) {
rangeCheck(index);
checkForComodification();
return l.get(index+offset);
}
public int size() {
checkForComodification();
return size;
}
public void add(int index, E element) {
rangeCheckForAdd(index);
checkForComodification();
l.add(index+offset, element);
this.modCount = l.modCount;
size++;
}
public E remove(int index) {
rangeCheck(index);
checkForComodification();
E result = l.remove(index+offset);
this.modCount = l.modCount;
size--;
return result;
}
protected void removeRange(int fromIndex, int toIndex) {
checkForComodification();
l.removeRange(fromIndex+offset, toIndex+offset);
this.modCount = l.modCount;
size -= (toIndex-fromIndex);
}
public boolean addAll(Collection c) {
return addAll(size, c);
}
public boolean addAll(int index, Collection c) {
rangeCheckForAdd(index);
int cSize = c.size();
if (cSize==0)
return false;
checkForComodification();
l.addAll(offset+index, c);
this.modCount = l.modCount;
size += cSize;
return true;
}
public Iterator iterator() {
return listIterator();
}
public ListIterator listIterator(final int index) {
checkForComodification();
rangeCheckForAdd(index);
return new ListIterator() {
private final ListIterator i = l.listIterator(index+offset);
public boolean hasNext() {
return nextIndex() < size;
}
public E next() {
if (hasNext())
return i.next();
else
throw new NoSuchElementException();
}
public boolean hasPrevious() {
return previousIndex() >= 0;
}
public E previous() {
if (hasPrevious())
return i.previous();
else
throw new NoSuchElementException();
}
public int nextIndex() {
return i.nextIndex() - offset;
}
public int previousIndex() {
return i.previousIndex() - offset;
}
public void remove() {
i.remove();
SubList.this.modCount = l.modCount;
size--;
}
public void set(E e) {
i.set(e);
}
public void add(E e) {
i.add(e);
SubList.this.modCount = l.modCount;
size++;
}
};
}
public List subList(int fromIndex, int toIndex) {
return new SubList<>(this, fromIndex, toIndex);
}
private void rangeCheck(int index) {
if (index < 0 || index >= size)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
private void rangeCheckForAdd(int index) {
if (index < 0 || index > size)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
private String outOfBoundsMsg(int index) {
return "Index: "+index+", Size: "+size;
}
private void checkForComodification() {
if (this.modCount != l.modCount)
throw new ConcurrentModificationException();
}
}
class RandomAccessSubList extends SubList implements RandomAccess {
RandomAccessSubList(AbstractList list, int fromIndex, int toIndex) {
super(list, fromIndex, toIndex);
}
public List subList(int fromIndex, int toIndex) {
return new RandomAccessSubList<>(this, fromIndex, toIndex);
}
}