PushbackIterator (Apache Commons Collections 4.2 API)

java.lang.Object
- org.apache.commons.collections4.iterators.PushbackIterator<E>

All Implemented Interfaces:

Iterator<E>
```
public class PushbackIterator<E>
extends Object
implements Iterator<E>
```
Decorates an iterator to support pushback of elements.
The decorator stores the pushed back elements in a LIFO manner: the last element that has been pushed back, will be returned as the next element in a call to next().
The decorator does not support the removal operation. Any call to remove() will result in an UnsupportedOperationException.

Since:

4.0

Constructor Summary

Constructors
Constructor Description

PushbackIterator(Iterator<? extends E> iterator)
Constructor.

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`boolean`	`hasNext()`
`E`	`next()`
`void`	`pushback(E item)`	Push back the given element to the iterator.
`static <E> PushbackIterator<E>`	`pushbackIterator(Iterator<? extends E> iterator)`	Decorates the specified iterator to support one-element lookahead.
`void`	`remove()`	This iterator will always throw an `UnsupportedOperationException`.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface java.util.Iterator
forEachRemaining

- Constructor Detail
  - PushbackIterator
```
public PushbackIterator(Iterator<? extends E> iterator)
```
    Constructor.
    
    Parameters:
    
    iterator - the iterator to decorate
- Method Detail
  - pushbackIterator
```
public static <E> PushbackIterator<E> pushbackIterator(Iterator<? extends E> iterator)
```
    Decorates the specified iterator to support one-element lookahead.
    If the iterator is already a PushbackIterator it is returned directly.
    
    Type Parameters:
    
    E - the element type
    
    Parameters:
    
    iterator - the iterator to decorate
    
    Returns:
    
    a new peeking iterator
    
    Throws:
    
    NullPointerException - if the iterator is null
  - pushback
```
public void pushback(E item)
```
    Push back the given element to the iterator.
    Calling next() immediately afterwards will return exactly this element.
    
    Parameters:
    
    item - the element to push back to the iterator
  - hasNext
```
public boolean hasNext()
```
    Specified by:
    
    hasNext in interface Iterator<E>
  - next
```
public E next()
```
    Specified by:
    
    next in interface Iterator<E>
  - remove
```
public void remove()
```
    This iterator will always throw an UnsupportedOperationException.
    
    Specified by:
    
    remove in interface Iterator<E>
    
    Throws:
    
    UnsupportedOperationException - always