com.google.common.base

Class Suppliers

java.lang.Object

com.google.common.base.Suppliers

@GwtCompatible
public final class Suppliers
extends Object

Useful suppliers.

All methods return serializable suppliers as long as they're given serializable parameters.

Since:

2.0

Author:

Laurence Gonsalves, Harry Heymann

Method Summary

Modifier and Type	Method and Description
static <F,T> Supplier<T>	compose(Function<? super F,T> function, Supplier<F> supplier) Returns a new supplier which is the composition of the provided function and supplier.
static <T> Supplier<T>	memoize(Supplier<T> delegate) Returns a supplier which caches the instance retrieved during the first call to get() and returns that value on subsequent calls to get().
static <T> Supplier<T>	memoizeWithExpiration(Supplier<T> delegate, long duration, TimeUnit unit) Returns a supplier that caches the instance supplied by the delegate and removes the cached value after the specified time has passed.
static <T> Supplier<T>	ofInstance(T instance) Returns a supplier that always supplies instance.
static <T> Function<Supplier<T>,T>	supplierFunction() Returns a function that accepts a supplier and returns the result of invoking Supplier.get() on that supplier.
static <T> Supplier<T>	synchronizedSupplier(Supplier<T> delegate) Returns a supplier whose get() method synchronizes on delegate before calling it, making it thread-safe.

Methods inherited from class java.lang.Object

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

Method Detail

compose

public static <F,T> Supplier<T> compose(Function<? super F,T> function,
                                        Supplier<F> supplier)

Returns a new supplier which is the composition of the provided function and supplier. In other words, the new supplier's value will be computed by retrieving the value from supplier, and then applying function to that value. Note that the resulting supplier will not call supplier or invoke function until it is called.

memoize

public static <T> Supplier<T> memoize(Supplier<T> delegate)

Returns a supplier which caches the instance retrieved during the first call to get() and returns that value on subsequent calls to get(). See: memoization

The returned supplier is thread-safe. The delegate's get() method will be invoked at most once unless the underlying get() throws an exception. The supplier's serialized form does not contain the cached value, which will be recalculated when get() is called on the reserialized instance.

When the underlying delegate throws an exception then this memoizing supplier will keep delegating calls until it returns valid data.

If delegate is an instance created by an earlier call to memoize, it is returned directly.

memoizeWithExpiration

public static <T> Supplier<T> memoizeWithExpiration(Supplier<T> delegate,
                                                    long duration,
                                                    TimeUnit unit)

Returns a supplier that caches the instance supplied by the delegate and removes the cached value after the specified time has passed. Subsequent calls to get() return the cached value if the expiration time has not passed. After the expiration time, a new value is retrieved, cached, and returned. See: memoization

The returned supplier is thread-safe. The supplier's serialized form does not contain the cached value, which will be recalculated when get() is called on the reserialized instance. The actual memoization does not happen when the underlying delegate throws an exception.

When the underlying delegate throws an exception then this memoizing supplier will keep delegating calls until it returns valid data.

Parameters:

duration - the length of time after a value is created that it should stop being returned by subsequent get() calls

unit - the unit that duration is expressed in

Throws:

IllegalArgumentException - if duration is not positive

Since:

2.0

ofInstance

public static <T> Supplier<T> ofInstance(@NullableDecl
                                         T instance)

Returns a supplier that always supplies instance.

synchronizedSupplier

public static <T> Supplier<T> synchronizedSupplier(Supplier<T> delegate)

Returns a supplier whose get() method synchronizes on delegate before calling it, making it thread-safe.

supplierFunction

public static <T> Function<Supplier<T>,T> supplierFunction()

Returns a function that accepts a supplier and returns the result of invoking Supplier.get() on that supplier.

Java 8 users: use the method reference Supplier::get instead.

Since:

8.0