PeekIterator

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

All Implemented Interfaces:

java.io.Closeable, java.lang.AutoCloseable, 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

Nested Classes
Modifier and Type	Class and Description
`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

Fields
Modifier and Type	Field and Description
`boolean`	`closed` TRUE if the iterator has been closed
`protected static PeekIterator<java.lang.Object>`	`EMPTY` An empty PeekIterator
`boolean`	`initialized` TRUE if next has received its first value
`T`	`next` Holds the next element (to be peeked)

Constructor Summary

Constructors
Constructor and Description

PeekIterator()

Constructors
Constructor and Description
`PeekIterator()`

Method Summary

All Methods Static Methods Instance Methods Abstract Methods Concrete Methods
Modifier and Type	Method and Description
`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
`protected abstract T`	`internalNext()` Returns the next or NULL if no next element is available
`protected T`	`internalSilentNext()` Wraps the Exceptions of internalNext into RuntimeExceptions
`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
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Iterator
forEachRemaining

Methods inherited from interface java.lang.Iterable
forEach, spliterator

- 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
  - EMPTY
```
protected static PeekIterator<java.lang.Object> EMPTY
```
    An empty PeekIterator
- 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>
  - internalSilentNext
```
protected final T internalSilentNext()
```
    Wraps the Exceptions of internalNext into RuntimeExceptions
  - internalNext
```
protected abstract T internalNext()
                           throws java.lang.Exception
```
    Returns the next or NULL if no next element is available
    
    Throws:
    
    java.lang.Exception
  - 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
    
    Specified by:
    
    close in interface java.lang.AutoCloseable
  - 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

Class PeekIterator<T>

Nested Class Summary

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Methods inherited from interface java.util.Iterator

Methods inherited from interface java.lang.Iterable

Field Detail

next

initialized

closed

EMPTY

Constructor Detail

PeekIterator

Method Detail

hasNext

internalSilentNext

internalNext

next

nextOrNull

remove

peek

iterator

close

asList

asList

asSet

asSet

asSet

toString

emptyIterator

numElements

numElements

toString

toString

list

list

main