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java.lang.Objectcom.google.common.base.Functions
@GwtCompatible public final class Functions
Useful functions.
All methods returns serializable functions as long as they're given serializable parameters.
Method Summary | ||
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static
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compose(Function<B,C> g,
Function<A,? extends B> f)
Returns the composition of two functions. |
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static
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constant(E value)
Creates a function that returns value for any input. |
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static
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forMap(Map<K,? extends V> map,
V defaultValue)
Returns a function which performs a map lookup with a default value. |
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static
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forMap(Map<K,V> map)
Returns a function which performs a map lookup. |
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static
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forPredicate(Predicate<T> predicate)
Creates a function that returns the same boolean output as the given predicate for all inputs. |
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static
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identity()
Returns the identity function. |
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static Function<Object,String> |
toStringFunction()
Returns a function that calls toString() on its argument. |
Methods inherited from class java.lang.Object |
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clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Method Detail |
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public static Function<Object,String> toStringFunction()
toString()
on its argument. The
function does not accept nulls; it will throw a
NullPointerException
when applied to null
.
public static <E> Function<E,E> identity()
public static <K,V> Function<K,V> forMap(Map<K,V> map)
The difference between a map and a function is that a map is defined on
a set of keys, while a function is defined on all inputs of the correct
type. The function created by this method returns null
for all
inputs that do not belong to the map's key set.
map
- source map that determines the function behavior
map.get(a)
for each a
public static <K,V> Function<K,V> forMap(Map<K,? extends V> map, @Nullable V defaultValue)
defaultValue
for all
inputs that do not belong to the map's key set.
map
- source map that determines the function behaviordefaultValue
- the value to return for inputs that aren't map keys
map.get(a)
when a
is a key,
or defaultValue
otherwisepublic static <A,B,C> Function<A,C> compose(Function<B,C> g, Function<A,? extends B> f)
f: A->B
and
g: B->C
, composition is defined as the function h such that
h(a) == g(f(a))
for each a
.
g
- the second function to applyf
- the first function to apply
f
and g
public static <T> Function<T,Boolean> forPredicate(Predicate<T> predicate)
public static <E> Function<Object,E> constant(@Nullable E value)
value
for any input.
value
- the constant value for the function to return
value
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