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java.lang.Objectcom.google.common.base.Functions
public final class Functions
Useful functions.
Field Summary | |
---|---|
static Function<Object,String> |
TO_STRING
See toStringFunction() . |
static Function<String,String> |
TRIM_STRING
See trimString() . |
Method Summary | ||
---|---|---|
static
|
compose(Function<? super B,? extends C> g,
Function<? super A,? extends B> f)
Returns the composition of two functions. |
|
static
|
constant(E value)
Returns a Function that returns value for any input. |
|
static
|
forMap(Map<? super A,? extends B> map)
Returns a function which performs key-to-value lookup on map . |
|
static
|
forMap(Map<? super A,? extends B> map,
B defaultValue)
Returns a function which performs key-to-value lookup on map . |
|
static
|
forPredicate(Predicate<? super T> predicate)
Returns a boolean-valued function that evaluates to the same result as the given predicate. |
|
static
|
identity()
Returns the identity function. |
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static Function<Object,Integer> |
toHashCode()
Returns a function that determines the Object.hashCode() of its
argument. |
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static
|
toStringFunction()
Returns a function that returns the Object.toString() value of its
argument. |
|
static Function<String,String> |
trimString()
A function that returns the result of calling String.trim()
on its argument. |
Methods inherited from class java.lang.Object |
---|
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Field Detail |
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public static final Function<Object,String> TO_STRING
toStringFunction()
.
TODO: Consider deprecating this in favor of an accessor method like
toStringFunction()
.
public static final Function<String,String> TRIM_STRING
trimString()
.
TODO: Deprecate this and use trimString().
Method Detail |
---|
public static <F> Function<F,String> toStringFunction()
Object.toString()
value of its
argument. This function is not nullable; invoking apply(null)
on it
throws a NullPointerException
.
public static Function<Object,Integer> toHashCode()
Object.hashCode()
of its
argument. For null arguments, this returns 0, as used in hash code
calculations by the Java Collections classes.
public static Function<String,String> trimString()
String.trim()
on its argument. Note that this function is not @Nullable:
it will throw a NullPointerException
when applied to null
.
public static <E> Function<E,E> identity()
public static <A,B> Function<A,B> forMap(Map<? super A,? extends B> map)
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 a type.
The function built by this method returns null
for all arguments that do not belong to the map's keyset.
map
- Map<A,B> source map
public static <A,B> Function<A,B> forMap(Map<? super A,? extends B> map, @Nullable B defaultValue)
map
.
The function built by this method returns defaultValue
for all its arguments that do not belong to the map's keyset.
map
- Map<A,B>defaultValue
- B
f
such that f(a)=map.get(a)
if map.containsKey(x)
, and defaultValue
otherwise.forMap(Map)
public static <A,B,C> Function<A,C> compose(Function<? super B,? extends C> g, Function<? super A,? extends B> f)
f: A->B
and
g: B->C
, composition is defined as the function h such that
h(x) == g(f(x))
for each x
.
g
- Function<B,C>f
- Function<A,B>
public static <T> Function<T,Boolean> forPredicate(Predicate<? super T> predicate)
public static <E> Function<Object,E> constant(@Nullable E value)
Function
that returns value
for any input.
value
- the constant value for the Function
to return
Function
that always returns value
.
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