Package net.cscott.jutil

Class FilterIterator<A,B>

java.lang.Object

net.cscott.jutil.FilterIterator<A,B>

All Implemented Interfaces:

Iterator<B>

public class FilterIterator<A,B>
extends Object
implements Iterator<B>

A FilterIterator filters and maps a source Iterator to generate a new one: it returns map.apply(o) for each element o of the source for which filter.test(o) is true.

 Iterator<String> names = FilterIterator.map(people, Person::name);
 Iterator<Person> adults = FilterIterator.filter(people, p -> p.age() >= 18);
 

A Stream does the same, with stream.filter(filter).map(map).iterator().

Note that this implementation reads one element ahead, so if the filter changes for an object 'o' between the time that is read (when next() is called, returning the object preceding 'o', and checking that 'o' satisfies the current filter) and the time when hasNext() is called, 'o' will still be returned, regardless of what the filter now says about it. Thus, it is recommended that only filters which remain consistent throughout the iteration be used.

Author:

C. Scott Ananian <cananian@alumni.princeton.edu>

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	FilterIterator.Filter<A,B>	Deprecated. Use a Predicate and a Function, which can be lambdas, with FilterIterator(Iterator,Predicate,Function), filter(Iterator,Predicate) or map(Iterator,Function).

Constructor Summary

Constructors

Constructor	Description
FilterIterator(Iterator<? extends A> i, Predicate<? super A> filter, Function<? super A,? extends B> map)	Creates a FilterIterator which returns map.apply(o) for each element o of i for which filter.test(o) is true.
FilterIterator(Iterator<A> i, FilterIterator.Filter<A,B> f)	Deprecated. Use FilterIterator(Iterator,Predicate,Function), or filter(Iterator,Predicate) or map(Iterator,Function), with lambdas instead of a FilterIterator.Filter.

Method Summary

Modifier and Type	Method	Description
static <A> FilterIterator<A,A>	filter(Iterator<? extends A> i, Predicate<? super A> filter)	Returns an Iterator over the elements of i for which filter.test() is true.
boolean	hasNext()
static <A, B> FilterIterator<A,B>	map(Iterator<? extends A> i, Function<? super A,? extends B> map)	Returns an Iterator over map.apply(o) for each element o of i.
B	next()

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, remove

Constructor Details

FilterIterator

public FilterIterator(Iterator<? extends A> i,
 Predicate<? super A> filter,
 Function<? super A,? extends B> map)

Creates a FilterIterator which returns map.apply(o) for each element o of i for which filter.test(o) is true.

Since:

2.0

FilterIterator

@Deprecated(since="2.0")
public FilterIterator(Iterator<A> i,
 FilterIterator.Filter<A,B> f)

Deprecated.

Use FilterIterator(Iterator,Predicate,Function), or filter(Iterator,Predicate) or map(Iterator,Function), with lambdas instead of a FilterIterator.Filter.

Creates a FilterIterator.

Method Details

filter

public static <A> FilterIterator<A,A> filter(Iterator<? extends A> i,
 Predicate<? super A> filter)

Returns an Iterator over the elements of i for which filter.test() is true.

Since:

2.0

map

public static <A,
B> FilterIterator<A,B> map(Iterator<? extends A> i,
 Function<? super A,? extends B> map)

Returns an Iterator over map.apply(o) for each element o of i.

Since:

2.0

next

public B next()

Specified by:

next in interface Iterator<A>

hasNext

public boolean hasNext()

Specified by:

hasNext in interface Iterator<A>