Stack

public class Stack extends Vector<E>

The Stack class represents a last-in-first-out (LIFO) stack of objects. It extends class Vector with five operations that allow a vector to be treated as a stack. The usual push and pop operations are provided, as well as a method to peek at the top item on the stack, a method to test for whether the stack is empty, and a method to search the stack for an item and discover how far it is from the top.

When a stack is first created, it contains no items.

A more complete and consistent set of LIFO stack operations is provided by the Deque interface and its implementations, which should be used in preference to this class. For example:

   Deque<Integer> stack = new ArrayDeque<Integer>();

Inherited Field Summary

From class java.util.Vector

protected int	capacityIncrement	The amount by which the capacity of the vector is automatically incremented when its size becomes greater than its capacity.
protected int	elementCount	The number of valid components in this Vector object.
protected Object[]	elementData	The array buffer into which the components of the vector are stored.

From class java.util.AbstractList

protected int

modCount

The number of times this list has been structurally modified.

Public Constructor Summary

Stack() Creates an empty Stack.

Public Method Summary

boolean	empty() Tests if this stack is empty.
synchronized E	peek() Looks at the object at the top of this stack without removing it from the stack.
synchronized E	pop() Removes the object at the top of this stack and returns that object as the value of this function.
E	push(E item) Pushes an item onto the top of this stack.
synchronized int	search(Object o) Returns the 1-based position where an object is on this stack.

Inherited Method Summary

From class java.util.Vector

void	add(int index, E element) Inserts the specified element at the specified position in this Vector.
synchronized boolean	add(E e) Appends the specified element to the end of this Vector.
synchronized boolean	addAll(int index, Collection<? extends E> c) Inserts all of the elements in the specified Collection into this Vector at the specified position.
synchronized boolean	addAll(Collection<? extends E> c) Appends all of the elements in the specified Collection to the end of this Vector, in the order that they are returned by the specified Collection's Iterator.
synchronized void	addElement(E obj) Adds the specified component to the end of this vector, increasing its size by one.
synchronized int	capacity() Returns the current capacity of this vector.
void	clear() Removes all of the elements from this Vector.
synchronized Object	clone() Returns a clone of this vector.
boolean	contains(Object o) Returns true if this vector contains the specified element.
synchronized boolean	containsAll(Collection<?> c) Returns true if this Vector contains all of the elements in the specified Collection.
synchronized void	copyInto(Object[] anArray) Copies the components of this vector into the specified array.
synchronized E	elementAt(int index) Returns the component at the specified index.
Enumeration<E>	elements() Returns an enumeration of the components of this vector.
synchronized void	ensureCapacity(int minCapacity) Increases the capacity of this vector, if necessary, to ensure that it can hold at least the number of components specified by the minimum capacity argument.
synchronized boolean	equals(Object o) Compares the specified Object with this Vector for equality.
synchronized E	firstElement() Returns the first component (the item at index 0) of this vector.
synchronized void	forEach(Consumer<? super E> action)
synchronized E	get(int index) Returns the element at the specified position in this Vector.
synchronized int	hashCode() Returns the hash code value for this Vector.
int	indexOf(Object o) Returns the index of the first occurrence of the specified element in this vector, or -1 if this vector does not contain the element.
synchronized int	indexOf(Object o, int index) Returns the index of the first occurrence of the specified element in this vector, searching forwards from index, or returns -1 if the element is not found.
synchronized void	insertElementAt(E obj, int index) Inserts the specified object as a component in this vector at the specified index.
synchronized boolean	isEmpty() Tests if this vector has no components.
synchronized Iterator<E>	iterator() Returns an iterator over the elements in this list in proper sequence.
synchronized E	lastElement() Returns the last component of the vector.
synchronized int	lastIndexOf(Object o) Returns the index of the last occurrence of the specified element in this vector, or -1 if this vector does not contain the element.
synchronized int	lastIndexOf(Object o, int index) Returns the index of the last occurrence of the specified element in this vector, searching backwards from index, or returns -1 if the element is not found.
synchronized ListIterator<E>	listIterator(int index) Returns a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list.
synchronized ListIterator<E>	listIterator() Returns a list iterator over the elements in this list (in proper sequence).
boolean	remove(Object o) Removes the first occurrence of the specified element in this Vector If the Vector does not contain the element, it is unchanged.
synchronized E	remove(int index) Removes the element at the specified position in this Vector.
synchronized boolean	removeAll(Collection<?> c) Removes from this Vector all of its elements that are contained in the specified Collection.
synchronized void	removeAllElements() Removes all components from this vector and sets its size to zero.
synchronized boolean	removeElement(Object obj) Removes the first (lowest-indexed) occurrence of the argument from this vector.
synchronized void	removeElementAt(int index) Deletes the component at the specified index.
synchronized boolean	removeIf(Predicate<? super E> filter) Removes all of the elements of this collection that satisfy the given predicate.
synchronized void	removeRange(int fromIndex, int toIndex) Removes from this list all of the elements whose index is between fromIndex, inclusive, and toIndex, exclusive.
synchronized void	replaceAll(UnaryOperator<E> operator) Replaces each element of this list with the result of applying the operator to that element.
synchronized boolean	retainAll(Collection<?> c) Retains only the elements in this Vector that are contained in the specified Collection.
synchronized E	set(int index, E element) Replaces the element at the specified position in this Vector with the specified element.
synchronized void	setElementAt(E obj, int index) Sets the component at the specified index of this vector to be the specified object.
synchronized void	setSize(int newSize) Sets the size of this vector.
synchronized int	size() Returns the number of components in this vector.
synchronized void	sort(Comparator<? super E> c) Sorts this list according to the order induced by the specified Comparator.
Spliterator<E>	spliterator() Creates a late-binding and fail-fast Spliterator over the elements in this list.
synchronized List<E>	subList(int fromIndex, int toIndex) Returns a view of the portion of this List between fromIndex, inclusive, and toIndex, exclusive.
synchronized Object[]	toArray() Returns an array containing all of the elements in this Vector in the correct order.
synchronized <T> T[]	toArray(T[] a) Returns an array containing all of the elements in this Vector in the correct order; the runtime type of the returned array is that of the specified array.
synchronized String	toString() Returns a string representation of this Vector, containing the String representation of each element.
synchronized void	trimToSize() Trims the capacity of this vector to be the vector's current size.

From class java.util.AbstractList

void	add(int index, E element) Inserts the specified element at the specified position in this list (optional operation).
boolean	add(E e) Appends the specified element to the end of this list (optional operation).
boolean	addAll(int index, Collection<? extends E> c) Inserts all of the elements in the specified collection into this list at the specified position (optional operation).
void	clear() Removes all of the elements from this list (optional operation).
boolean	equals(Object o) Compares the specified object with this list for equality.
abstract E	get(int index) Returns the element at the specified position in this list.
int	hashCode() Returns the hash code value for this list.
int	indexOf(Object o) Returns the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element.
Iterator<E>	iterator() Returns an iterator over the elements in this list in proper sequence.
int	lastIndexOf(Object o) Returns the index of the last occurrence of the specified element in this list, or -1 if this list does not contain the element.
ListIterator<E>	listIterator(int index) Returns a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list.
ListIterator<E>	listIterator() Returns a list iterator over the elements in this list (in proper sequence).
E	remove(int index) Removes the element at the specified position in this list (optional operation).
void	removeRange(int fromIndex, int toIndex) Removes from this list all of the elements whose index is between fromIndex, inclusive, and toIndex, exclusive.
E	set(int index, E element) Replaces the element at the specified position in this list with the specified element (optional operation).
List<E>	subList(int fromIndex, int toIndex) Returns a view of the portion of this list between the specified fromIndex, inclusive, and toIndex, exclusive.

From class java.util.AbstractCollection

boolean	add(E e) Ensures that this collection contains the specified element (optional operation). This implementation always throws an UnsupportedOperationException.
boolean	addAll(Collection<? extends E> c) Adds all of the elements in the specified collection to this collection (optional operation). This implementation iterates over the specified collection, and adds each object returned by the iterator to this collection, in turn.
void	clear() Removes all of the elements from this collection (optional operation). This implementation iterates over this collection, removing each element using the Iterator.remove operation.
boolean	contains(Object o) Returns true if this collection contains the specified element. This implementation iterates over the elements in the collection, checking each element in turn for equality with the specified element.
boolean	containsAll(Collection<?> c) Returns true if this collection contains all of the elements in the specified collection. This implementation iterates over the specified collection, checking each element returned by the iterator in turn to see if it's contained in this collection.
boolean	isEmpty() Returns true if this collection contains no elements. This implementation returns size() == 0.
abstract Iterator<E>	iterator() Returns an iterator over the elements contained in this collection.
boolean	remove(Object o) Removes a single instance of the specified element from this collection, if it is present (optional operation). This implementation iterates over the collection looking for the specified element.
boolean	removeAll(Collection<?> c) Removes all of this collection's elements that are also contained in the specified collection (optional operation). This implementation iterates over this collection, checking each element returned by the iterator in turn to see if it's contained in the specified collection.
boolean	retainAll(Collection<?> c) Retains only the elements in this collection that are contained in the specified collection (optional operation). This implementation iterates over this collection, checking each element returned by the iterator in turn to see if it's contained in the specified collection.
abstract int	size() Returns the number of elements in this collection.
<T> T[]	toArray(T[] contents) Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array. This implementation returns an array containing all the elements returned by this collection's iterator in the same order, stored in consecutive elements of the array, starting with index 0.
Object[]	toArray() Returns an array containing all of the elements in this collection. This implementation returns an array containing all the elements returned by this collection's iterator, in the same order, stored in consecutive elements of the array, starting with index 0.
String	toString() Returns a string representation of this collection.

From class java.lang.Object

Object	clone() Creates and returns a copy of this Object.
boolean	equals(Object obj) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of Class that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait(long timeout, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait(long timeout) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.

From interface java.util.List

abstract boolean	add(E e) Appends the specified element to the end of this list (optional operation).
abstract void	add(int index, E element) Inserts the specified element at the specified position in this list (optional operation).
abstract boolean	addAll(Collection<? extends E> c) Appends all of the elements in the specified collection to the end of this list, in the order that they are returned by the specified collection's iterator (optional operation).
abstract boolean	addAll(int index, Collection<? extends E> c) Inserts all of the elements in the specified collection into this list at the specified position (optional operation).
abstract void	clear() Removes all of the elements from this list (optional operation).
abstract boolean	contains(Object o) Returns true if this list contains the specified element.
abstract boolean	containsAll(Collection<?> c) Returns true if this list contains all of the elements of the specified collection.
abstract boolean	equals(Object o) Compares the specified object with this list for equality.
abstract E	get(int index) Returns the element at the specified position in this list.
abstract int	hashCode() Returns the hash code value for this list.
abstract int	indexOf(Object o) Returns the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element.
abstract boolean	isEmpty() Returns true if this list contains no elements.
abstract Iterator<E>	iterator() Returns an iterator over the elements in this list in proper sequence.
abstract int	lastIndexOf(Object o) Returns the index of the last occurrence of the specified element in this list, or -1 if this list does not contain the element.
abstract ListIterator<E>	listIterator(int index) Returns a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list.
abstract ListIterator<E>	listIterator() Returns a list iterator over the elements in this list (in proper sequence).
abstract E	remove(int index) Removes the element at the specified position in this list (optional operation).
abstract boolean	remove(Object o) Removes the first occurrence of the specified element from this list, if it is present (optional operation).
abstract boolean	removeAll(Collection<?> c) Removes from this list all of its elements that are contained in the specified collection (optional operation).
void	replaceAll(UnaryOperator<E> operator) Replaces each element of this list with the result of applying the operator to that element.
abstract boolean	retainAll(Collection<?> c) Retains only the elements in this list that are contained in the specified collection (optional operation).
abstract E	set(int index, E element) Replaces the element at the specified position in this list with the specified element (optional operation).
abstract int	size() Returns the number of elements in this list.
void	sort(Comparator<? super E> c) Sorts this list according to the order induced by the specified Comparator.
Spliterator<E>	spliterator() Creates a Spliterator over the elements in this list.
abstract List<E>	subList(int fromIndex, int toIndex) Returns a view of the portion of this list between the specified fromIndex, inclusive, and toIndex, exclusive.
abstract Object[]	toArray() Returns an array containing all of the elements in this list in proper sequence (from first to last element).
abstract <T> T[]	toArray(T[] a) Returns an array containing all of the elements in this list in proper sequence (from first to last element); the runtime type of the returned array is that of the specified array.

From interface java.util.Collection

abstract boolean	add(E e) Ensures that this collection contains the specified element (optional operation).
abstract boolean	addAll(Collection<? extends E> c) Adds all of the elements in the specified collection to this collection (optional operation).
abstract void	clear() Removes all of the elements from this collection (optional operation).
abstract boolean	contains(Object o) Returns true if this collection contains the specified element.
abstract boolean	containsAll(Collection<?> c) Returns true if this collection contains all of the elements in the specified collection.
abstract boolean	equals(Object o) Compares the specified object with this collection for equality.
abstract int	hashCode() Returns the hash code value for this collection.
abstract boolean	isEmpty() Returns true if this collection contains no elements.
abstract Iterator<E>	iterator() Returns an iterator over the elements in this collection.
Stream<E>	parallelStream() Returns a possibly parallel Stream with this collection as its source.
abstract boolean	remove(Object o) Removes a single instance of the specified element from this collection, if it is present (optional operation).
abstract boolean	removeAll(Collection<?> c) Removes all of this collection's elements that are also contained in the specified collection (optional operation).
boolean	removeIf(Predicate<? super E> filter) Removes all of the elements of this collection that satisfy the given predicate.
abstract boolean	retainAll(Collection<?> c) Retains only the elements in this collection that are contained in the specified collection (optional operation).
abstract int	size() Returns the number of elements in this collection.
Spliterator<E>	spliterator() Creates a Spliterator over the elements in this collection.
Stream<E>	stream() Returns a sequential Stream with this collection as its source.
abstract <T> T[]	toArray(T[] a) Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array.
abstract Object[]	toArray() Returns an array containing all of the elements in this collection.

From interface java.lang.Iterable

void	forEach(Consumer<? super T> action) Performs the given action for each element of the Iterable until all elements have been processed or the action throws an exception.
abstract Iterator<E>	iterator() Returns an iterator over elements of type T.
Spliterator<E>	spliterator() Creates a Spliterator over the elements described by this Iterable.

Public Constructors

public Stack ()

Creates an empty Stack.

Public Methods

public boolean empty ()

Tests if this stack is empty.

Returns

• true if and only if this stack contains no items; false otherwise.

public synchronized E peek ()

Looks at the object at the top of this stack without removing it from the stack.

Returns

• the object at the top of this stack (the last item of the Vector object).

Throws

EmptyStackException	if this stack is empty.

public synchronized E pop ()

Removes the object at the top of this stack and returns that object as the value of this function.

Returns

• The object at the top of this stack (the last item of the Vector object).

Throws

EmptyStackException	if this stack is empty.

public E push (E item)

Pushes an item onto the top of this stack. This has exactly the same effect as:

 addElement(item)

Parameters

item	the item to be pushed onto this stack.

Returns

• the item argument.

See Also

• Vector.addElement(E)

public synchronized int search (Object o)

Returns the 1-based position where an object is on this stack. If the object o occurs as an item in this stack, this method returns the distance from the top of the stack of the occurrence nearest the top of the stack; the topmost item on the stack is considered to be at distance 1. The equals method is used to compare o to the items in this stack.

Parameters

o	the desired object.

Returns

• the 1-based position from the top of the stack where the object is located; the return value -1 indicates that the object is not on the stack.