PeekIterator (de.mpg.mpi-inf:javatools 1.1 API)

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

All Implemented Interfaces:

Closeable, AutoCloseable, Iterable<T>, Iterator<T>

Direct Known Subclasses:

CSVLines, DeepFileSet, FileLines, FilteredIterator, MatchReader, PeekIterator.ElementaryPeekIterator, PeekIterator.SimplePeekIterator, ResultIterator
```
public abstract class PeekIterator<T>
extends Object
implements Iterator<T>, Iterable<T>, Closeable
```
Copyright 2016 Fabian M. Suchanek Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. 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<Object>`	`EMPTY` An empty PeekIterator
`boolean`	`fetchedNextValue` TRUE if variable next contains the next 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
`List<T>`	`asList()` Returns an arraylist of this iterator (killing this iterator)
`static <T> List<T>`	`asList(Iterator<T> i)` Returns an arraylist of an iterator (killing the iterator)
`Set<T>`	`asSet()` Returns a hashset of this iterator (killing this iterator)
`static <T> Set<T>`	`asSet(Iterator<T> i)` Returns a hashset of an iterator (killing the iterator)
`static <T> Set<T>`	`asSet(Iterator<T> i, 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
`Iterator<T>`	`iterator()` returns this
`static <S> List<S>`	`list(Iterable<S> it)` Lists the elements in an iterable
`static <S> List<S>`	`list(Iterator<S> it)` Lists the elements in an iterator (and destroys it)
`static void`	`main(String[] args)` test routine
`T`	`next()` Returns the next element and advances.
`T`	`nextOrNull()` Returns the next element and advances.
`static <S> int`	`numElements(Iterable<S> it)` Counts the number of elements in an iterable
`static <S> int`	`numElements(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
`String`	`toString()`
`static <S> StringBuilder`	`toString(Iterable<S> it)` Lists the elements in an iterable
`static <S> StringBuilder`	`toString(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)
  - fetchedNextValue
```
public boolean fetchedNextValue
```
    TRUE if variable next contains the next value
  - closed
```
public boolean closed
```
    TRUE if the iterator has been closed
  - EMPTY
```
protected static PeekIterator<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 Iterator<T>
  - internalSilentNext
```
protected final T internalSilentNext()
```
    Wraps the Exceptions of internalNext into RuntimeExceptions
  - internalNext
```
protected abstract T internalNext()
                           throws Exception
```
    Returns the next or NULL if no next element is available
    
    Throws:
    
    Exception
  - next
```
public final T next()
```
    Returns the next element and advances. Overwrite internalNext instead!
    
    Specified by:
    
    next in interface 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 Iterator<T>
  - peek
```
public final T peek()
```
    returns the next element without advancing
  - iterator
```
public Iterator<T> iterator()
```
    returns this
    
    Specified by:
    
    iterator in interface Iterable<T>
  - close
```
public void close()
```
    Closes the underlying resource
    
    Specified by:
    
    close in interface Closeable
    
    Specified by:
    
    close in interface AutoCloseable
  - asList
```
public static <T> List<T> asList(Iterator<T> i)
```
    Returns an arraylist of an iterator (killing the iterator)
  - asList
```
public List<T> asList()
```
    Returns an arraylist of this iterator (killing this iterator)
  - asSet
```
public static <T> Set<T> asSet(Iterator<T> i,
                               Set<T> set)
```
    Fills the elements of an iterator into a given set (killing the iterator)
  - asSet
```
public static <T> Set<T> asSet(Iterator<T> i)
```
    Returns a hashset of an iterator (killing the iterator)
  - asSet
```
public Set<T> asSet()
```
    Returns a hashset of this iterator (killing this iterator)
  - toString
```
public String toString()
```
    Overrides:
    
    toString in class Object
  - emptyIterator
```
public static <K> PeekIterator<K> emptyIterator()
```
    returns a constant empty iterator
  - numElements
```
public static <S> int numElements(Iterator<S> it)
```
    Counts the number of elements in an iterator (and destroys it)
  - numElements
```
public static <S> int numElements(Iterable<S> it)
```
    Counts the number of elements in an iterable
  - toString
```
public static <S> StringBuilder toString(Iterable<S> it)
```
    Lists the elements in an iterable
  - toString
```
public static <S> StringBuilder toString(Iterator<S> it)
```
    Lists the elements in an iterator (and destroys it)
  - list
```
public static <S> List<S> list(Iterable<S> it)
```
    Lists the elements in an iterable
  - list
```
public static <S> List<S> list(Iterator<S> it)
```
    Lists the elements in an iterator (and destroys it)
  - main
```
public static void main(String[] args)
                 throws Exception
```
    test routine
    
    Throws:
    
    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

fetchedNextValue

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