org.jjoost.util
Class Functions

java.lang.Object
  org.jjoost.util.Functions

public class Functions
extends java.lang.Object

A class defining simple functions, and methods for working with functions

Author:

b.elliottsmith

Nested Class Summary

static class	Functions.AbstractValueProjection<E extends Value<V>,V> A function that retrieves the value from a Value
static class	Functions.FieldProjection<E,F> A Function which accepts a Field (reflection API), which will be retrieved and returned from every object the function is applied to.
static class	Functions.MapEntryKeyProjection<E extends java.util.Map.Entry<K,?>,K> A function that retrieves the key portion of a Map.Entry
static class	Functions.MapEntryValueProjection<E extends java.util.Map.Entry<?,V>,V> A function that retrieves the value portion of a Map.Entry
static class	Functions.MethodProjection<E,F> A Function which accepts a Method and arguments to provide to the method, which will execute the method on each object it receives as an argument, returning the result.

Constructor Summary

Functions()

Method Summary

static <E,F> ClosableIterator<F>	apply(ClosableIterator<? extends E> iter, Function<? super E,? extends F> f) /** Returns a new iterator which returns f.f(iter.next()) for each call to next() in the resulting iterator.
static <E,F> ClosableIterator<F>	apply(Function<? super E,? extends F> f, ClosableIterator<? extends E> iter) Returns a new iterator which returns f.f(iter.next()) for each call to next() in the resulting iterator.
static <E,F> java.lang.Iterable<F>	apply(Function<? super E,? extends F> f, java.lang.Iterable<? extends E> iter) Returns a new Iterable which lazily applies the provided function to all iterators constructed from it.
static <E,F> java.util.Iterator<F>	apply(Function<? super E,? extends F> f, java.util.Iterator<? extends E> iter) Returns a new iterator which returns f.f(iter.next()) for each call to next() in the resulting iterator.
static <E,F> java.util.List<F>	apply(Function<? super E,? extends F> f, java.util.List<? extends E> list) Creates a new ArrayList that contains the result of applying the provided function to every element in the provided list.
static <E,F> java.lang.Iterable<F>	apply(java.lang.Iterable<? extends E> iter, Function<? super E,? extends F> f) Returns a new Iterable which lazily applies the provided function to all iterators constructed from it.
static <E,F> java.util.Iterator<F>	apply(java.util.Iterator<? extends E> iter, Function<? super E,? extends F> f) Returns a new iterator which returns f.f(iter.next()) for each call to next() in the resulting iterator.
static <E,F> java.util.List<F>	apply(java.util.List<? extends E> list, Function<? super E,? extends F> f) Creates a new ArrayList that contains the result of applying the provided function to every element in the provided list.
static <E,F,G> Function<E,G>	composition(Function<F,G> f2, Function<E,F> f1) Returns a function that is the composition of the two provided functions; the function provided as the second argument is applied first, and the function provided as the first argument is then applied to the result of this, i.e.
static <E,F> Function<E,F>	getFieldProjection(java.lang.Class<E> clazz, java.lang.String propertyName, java.lang.Class<F> propertyType) Return a Function which retrieves the named field from each object it is applied to
static <K,E extends java.util.Map.Entry<? extends K,?>> Function<E,K>	getMapEntryKeyProjection() Return a function that retrieves the key portion of a Map.Entry
static <V,E extends java.util.Map.Entry<?,? extends V>> Function<E,V>	getMapEntryValueProjection() Return a function that retrieves the value portion of a Map.Entry
static <E,F> Function<E,F>	getMethodProjection(java.lang.Class<E> clazz, java.lang.String methodName, java.lang.Class<F> returnType) Return a Function which executes the named no-arg method on objects of the provided type
static <V> Function<Value<V>,V>	getValueContentsProjection() Return a function that retrieves the value from a Value object
static <E> Function<E,E>	identity() Returns the identity function, i.e.
static <E> Function<E,E>	replaceNullWith(E val) Returns a function that for all non-null inputs acts like the identity function (i.e.
static <E> Function<E,java.lang.String>	toString(boolean replaceNulls) Returns a function that converts its input to a String; if replaceNulls is true then null values are replaced by "null", otherwise they are left as null

Methods inherited from class java.lang.Object

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

Constructor Detail

Functions

public Functions()

Method Detail

identity

public static <E> Function<E,E> identity()

Returns the identity function, i.e. that returns its input as output

Type Parameters:

E - input type

Returns:

the identity function

toString

public static <E> Function<E,java.lang.String> toString(boolean replaceNulls)

Returns a function that converts its input to a String; if replaceNulls is true then null values are replaced by "null", otherwise they are left as null

Parameters:

replaceNulls - if true, replace nulls with "null"

Returns:

function that converts its input to a String

replaceNullWith

public static <E> Function<E,E> replaceNullWith(E val)

Returns a function that for all non-null inputs acts like the identity function (i.e. yields input as output), however replaces all null values it is applied to with the provided value

Parameters:

val - value to replace nulls with

Returns:

a function replacing nulls with the provided value

composition

public static <E,F,G> Function<E,G> composition(Function<F,G> f2,
                                                Function<E,F> f1)

Returns a function that is the composition of the two provided functions; the function provided as the second argument is applied first, and the function provided as the first argument is then applied to the result of this, i.e. returns f2.apply(f1.apply(v))

Parameters:

f2 - function applied second

f1 - function applied first

Returns:

composition of f1 and f2

getMethodProjection

public static <E,F> Function<E,F> getMethodProjection(java.lang.Class<E> clazz,
                                                      java.lang.String methodName,
                                                      java.lang.Class<F> returnType)
                                         throws java.lang.SecurityException,
                                                java.lang.NoSuchMethodException

Return a Function which executes the named no-arg method on objects of the provided type

Parameters:

clazz - function input type

methodName - name of the method to call

returnType - the return type of the method

Returns:

a Function which executes the named no-arg method on objects of the provided type

Throws:

java.lang.SecurityException - if a SecurityManager prevents access to the method

java.lang.NoSuchMethodException - if no no-args method of the provided name can be found in the provided class' hierarchy

getFieldProjection

public static <E,F> Function<E,F> getFieldProjection(java.lang.Class<E> clazz,
                                                     java.lang.String propertyName,
                                                     java.lang.Class<F> propertyType)
                                        throws java.lang.SecurityException,
                                               java.lang.NoSuchFieldException

Return a Function which retrieves the named field from each object it is applied to

Parameters:

clazz - the input type of the function

propertyName - the name of the property

propertyType - the type of the property

Returns:

a Function which retrieves the named field from each object it is applied to

Throws:

java.lang.SecurityException - if a SecurityManager prevents access to the method

java.lang.NoSuchFieldException - if a field of the provided name could not be found in the provided class

getMapEntryValueProjection

public static <V,E extends java.util.Map.Entry<?,? extends V>> Function<E,V> getMapEntryValueProjection()

Return a function that retrieves the value portion of a Map.Entry

Returns:

a function that retrieves the value portion of a Map.Entry

getMapEntryKeyProjection

public static <K,E extends java.util.Map.Entry<? extends K,?>> Function<E,K> getMapEntryKeyProjection()

Return a function that retrieves the key portion of a Map.Entry

Returns:

a function that retrieves the key portion of a Map.Entry

getValueContentsProjection

public static <V> Function<Value<V>,V> getValueContentsProjection()

Return a function that retrieves the value from a Value object

Returns:

a function that retrieves the value from a Value object

apply

public static <E,F> java.util.List<F> apply(Function<? super E,? extends F> f,
                                            java.util.List<? extends E> list)

Creates a new ArrayList that contains the result of applying the provided function to every element in the provided list. Equivalent to apply(list, f).

Parameters:

list - list to apply the function to

f - function to apply to the list

Returns:

a new ArrayList that contains the result of applying the provided function to every element in the provided list

apply

public static <E,F> java.util.List<F> apply(java.util.List<? extends E> list,
                                            Function<? super E,? extends F> f)

Creates a new ArrayList that contains the result of applying the provided function to every element in the provided list. Equivalent to apply(f, list).

Parameters:

list - list to apply the function to

f - function to apply to the list

Returns:

a new ArrayList that contains the result of applying the provided function to every element in the provided list

apply

public static <E,F> java.lang.Iterable<F> apply(Function<? super E,? extends F> f,
                                                java.lang.Iterable<? extends E> iter)

Returns a new Iterable which lazily applies the provided function to all iterators constructed from it. Equivalent to apply(iter, f).

Parameters:

iter - iterable to apply the function to

f - function to apply to the iterable

Returns:

a new Iterable which lazily applies the provided function to all iterators constructed from it

apply

public static <E,F> java.lang.Iterable<F> apply(java.lang.Iterable<? extends E> iter,
                                                Function<? super E,? extends F> f)

Returns a new Iterable which lazily applies the provided function to all iterators constructed from it. Equivalent to apply(f, iter).

Parameters:

iter - iterable to apply the function to

f - function to apply to the iterable

Returns:

a new Iterable which lazily applies the provided function to all iterators constructed from it

apply

public static <E,F> java.util.Iterator<F> apply(java.util.Iterator<? extends E> iter,
                                                Function<? super E,? extends F> f)

Returns a new iterator which returns f.f(iter.next()) for each call to next() in the resulting iterator. Equivalent to apply(f, iter).

Parameters:

iter - iterator to apply the function to

f - function to apply to the iterator

Returns:

a new iterator which return f.f(iter.next()) for each call to next()

apply

public static <E,F> java.util.Iterator<F> apply(Function<? super E,? extends F> f,
                                                java.util.Iterator<? extends E> iter)

Returns a new iterator which returns f.f(iter.next()) for each call to next() in the resulting iterator. Equivalent to apply(iter, f).

Parameters:

iter - iterator to apply the function to

f - function to apply to the iterator

Returns:

a new iterator which return f.f(iter.next()) for each call to next()

apply

public static <E,F> ClosableIterator<F> apply(ClosableIterator<? extends E> iter,
                                              Function<? super E,? extends F> f)

/** Returns a new iterator which returns f.f(iter.next()) for each call to next() in the resulting iterator. Equivalent to apply(f, iter).

Parameters:

iter - iterator to apply the function to

f - function to apply to the iterator

Returns:

a new iterator which return f.f(iter.next()) for each call to next()

apply

public static <E,F> ClosableIterator<F> apply(Function<? super E,? extends F> f,
                                              ClosableIterator<? extends E> iter)

Returns a new iterator which returns f.f(iter.next()) for each call to next() in the resulting iterator. Equivalent to apply(iter, f).

Parameters:

iter - iterator to apply the function to

f - function to apply to the iterator

Returns:

a new iterator which return f.f(iter.next()) for each call to next()