javatools.datatypes
Class PeekIterator<T>

java.lang.Object
  javatools.datatypes.PeekIterator<T>

All Implemented Interfaces:

java.io.Closeable, java.lang.Iterable<T>, java.util.Iterator<T>

Direct Known Subclasses:

CSVLines, DeepFileSet, FileLines, FilteredIterator, MatchReader, PeekIterator.ElementaryPeekIterator, PeekIterator.SimplePeekIterator, ResultIterator

public abstract class PeekIterator<T>
extends java.lang.Object
implements java.util.Iterator<T>, java.lang.Iterable<T>, java.io.Closeable

This class is part of the Java Tools (see http://mpii.de/yago-naga/javatools). It is licensed under the Creative Commons Attribution License (see http://creativecommons.org/licenses/by/3.0) by the YAGO-NAGA team (see http://mpii.de/yago-naga). This class provides an Iterator that can look ahead. With the method peek(), you can retrieve the next element without advancing the iterator.
Example:

    PeekIterator i=new SimplePeekIterator(1,2,3,4);
    i.peek();
    ---> 1
    i.peek();
    ---> 1    
    i.next();
    ---> 1
    i.peek();
    ---> 2    

The class is also suited to create an Interator by overriding. The only method that needs top be overwritten is "internalNext()".
Example:

    // An iterator over the numbers 0,1,2
    PeekIterator it=new PeekIterator() {
      int counter=0;
      // Returns null if there are no more elements
      protected Integer internalNext() throws Exception {
        if(counter==3) return(null);
        return(counter++);
      }
    };

    for(Integer i : it) D.p(i);

    --->
         0
         1
         2

Nested Class Summary

static class	PeekIterator.ElementaryPeekIterator<T> A Peek iterator with one single element
static class	PeekIterator.SimplePeekIterator<T> A PeekIterator that can iterate over another iterator or over a list of elements

Field Summary

boolean	closed TRUE if the iterator has been closed
boolean	initialized TRUE if next has received its first value
T	next Holds the next element (to be peeked)

Constructor Summary

PeekIterator()

Method Summary

java.util.List<T>	asList() Returns an arraylist of this iterator (killing this iterator)
static <T> java.util.List<T>	asList(java.util.Iterator<T> i) Returns an arraylist of an iterator (killing the iterator)
java.util.Set<T>	asSet() Returns a hashset of this iterator (killing this iterator)
static <T> java.util.Set<T>	asSet(java.util.Iterator<T> i) Returns a hashset of an iterator (killing the iterator)
static <T> java.util.Set<T>	asSet(java.util.Iterator<T> i, java.util.Set<T> set) Fills the elements of an iterator into a given set (killing the iterator)
void	close() Closes the underlying resource
static <K> PeekIterator<K>	emptyIterator() returns a constant empty iterator
boolean	hasNext() TRUE if there are more elements to get with getNext
java.util.Iterator<T>	iterator() returns this
static <S> java.util.List<S>	list(java.lang.Iterable<S> it) Lists the elements in an iterable
static <S> java.util.List<S>	list(java.util.Iterator<S> it) Lists the elements in an iterator (and destroys it)
static void	main(java.lang.String[] args) test routine
T	next() Returns the next element and advances.
T	nextOrNull() Returns the next element and advances.
static <S> int	numElements(java.lang.Iterable<S> it) Counts the number of elements in an iterable
static <S> int	numElements(java.util.Iterator<S> it) Counts the number of elements in an iterator (and destroys it)
T	peek() returns the next element without advancing
void	remove() Removes the current element, if supported by the underlying iterator
java.lang.String	toString()
static <S> java.lang.StringBuilder	toString(java.lang.Iterable<S> it) Lists the elements in an iterable
static <S> java.lang.StringBuilder	toString(java.util.Iterator<S> it) Lists the elements in an iterator (and destroys it)

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

next

public T next

Holds the next element (to be peeked)

initialized

public boolean initialized

TRUE if next has received its first value

closed

public boolean closed

TRUE if the iterator has been closed

Constructor Detail

PeekIterator

public PeekIterator()

Method Detail

hasNext

public final boolean hasNext()

TRUE if there are more elements to get with getNext

Specified by:

hasNext in interface java.util.Iterator<T>

next

public final T next()

Returns the next element and advances. Overwrite internalNext instead!

Specified by:

next in interface java.util.Iterator<T>

nextOrNull

public final T nextOrNull()

Returns the next element and advances. Overwrite internalNext instead!

remove

public void remove()

Removes the current element, if supported by the underlying iterator

Specified by:

remove in interface java.util.Iterator<T>

peek

public final T peek()

returns the next element without advancing

iterator

public java.util.Iterator<T> iterator()

returns this

Specified by:

iterator in interface java.lang.Iterable<T>

close

public void close()

Closes the underlying resource

Specified by:

close in interface java.io.Closeable

asList

public static <T> java.util.List<T> asList(java.util.Iterator<T> i)

Returns an arraylist of an iterator (killing the iterator)

asList

public java.util.List<T> asList()

Returns an arraylist of this iterator (killing this iterator)

asSet

public static <T> java.util.Set<T> asSet(java.util.Iterator<T> i,
                                         java.util.Set<T> set)

Fills the elements of an iterator into a given set (killing the iterator)

asSet

public static <T> java.util.Set<T> asSet(java.util.Iterator<T> i)

Returns a hashset of an iterator (killing the iterator)

asSet

public java.util.Set<T> asSet()

Returns a hashset of this iterator (killing this iterator)

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Object

emptyIterator

public static <K> PeekIterator<K> emptyIterator()

returns a constant empty iterator

numElements

public static <S> int numElements(java.util.Iterator<S> it)

Counts the number of elements in an iterator (and destroys it)

numElements

public static <S> int numElements(java.lang.Iterable<S> it)

Counts the number of elements in an iterable

toString

public static <S> java.lang.StringBuilder toString(java.lang.Iterable<S> it)

Lists the elements in an iterable

toString

public static <S> java.lang.StringBuilder toString(java.util.Iterator<S> it)

Lists the elements in an iterator (and destroys it)

list

public static <S> java.util.List<S> list(java.lang.Iterable<S> it)

Lists the elements in an iterable

list

public static <S> java.util.List<S> list(java.util.Iterator<S> it)

Lists the elements in an iterator (and destroys it)

main

public static void main(java.lang.String[] args)
                 throws java.lang.Exception

test routine

Throws:

java.lang.Exception