Package org.apache.hadoop.util.functional

Class LazyAtomicReference<T>

java.lang.Object

org.apache.hadoop.util.functional.LazyAtomicReference<T>

Type Parameters:

T - type of reference

All Implemented Interfaces:

java.util.function.Supplier<T>, CallableRaisingIOE<T>

Direct Known Subclasses:

LazyAutoCloseableReference

public class LazyAtomicReference<T>
extends java.lang.Object
implements CallableRaisingIOE<T>, java.util.function.Supplier<T>

A lazily constructed reference, whose reference constructor is a CallableRaisingIOE so may raise IOExceptions.

This constructor is only invoked on demand when the reference is first needed, after which the same value is returned. This value MUST NOT be null.

Implements CallableRaisingIOE and java.util.function.Supplier. An instance of this can therefore be used in a functional IO chain. As such, it can act as a delayed and caching invocator of a function: the supplier passed in is only ever invoked once, and only when requested.

Constructor Summary

Constructors

Constructor	Description
LazyAtomicReference(CallableRaisingIOE<? extends T> constructor)	Constructor for this instance.

Method Summary

Modifier and Type	Method	Description
T	apply()	Implementation of CallableRaisingIOE.apply().
T	eval()	Get the value, constructing it if needed.
T	get()	Implementation of Supplier.get().
protected CallableRaisingIOE<? extends T>	getConstructor()	Getter for the constructor.
protected java.util.concurrent.atomic.AtomicReference<T>	getReference()	Get the reference.
boolean	isSet()	Is the reference set?
static <T> LazyAtomicReference<T>	lazyAtomicReferenceFromSupplier(java.util.function.Supplier<T> supplier)	Create from a supplier.
java.lang.String	toString()

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.apache.hadoop.util.functional.CallableRaisingIOE

unchecked

Constructor Detail

LazyAtomicReference

public LazyAtomicReference(CallableRaisingIOE<? extends T> constructor)

Constructor for this instance.

Parameters:

constructor - method to invoke to actually construct the inner object.

Method Detail

getConstructor

protected CallableRaisingIOE<? extends T> getConstructor()

Getter for the constructor.

Returns:

the constructor class

getReference

protected java.util.concurrent.atomic.AtomicReference<T> getReference()

Get the reference. Subclasses working with this need to be careful working with this.

Returns:

the reference.

eval

public T eval()
       throws java.io.IOException

Get the value, constructing it if needed.

Returns:

the value

Throws:

java.io.IOException - on any evaluation failure

java.lang.NullPointerException - if the evaluated function returned null.

apply

public final T apply()
              throws java.io.IOException

Implementation of CallableRaisingIOE.apply(). Invoke eval().

Specified by:

apply in interface CallableRaisingIOE<T>

Returns:

the value

Throws:

java.io.IOException - on any evaluation failure

get

public final T get()
            throws java.io.UncheckedIOException

Implementation of Supplier.get().

Invoke eval() and convert IOEs to UncheckedIOException.

This is the Supplier.get() implementation, which allows this class to passed into anything taking a supplier.

Specified by:

get in interface java.util.function.Supplier<T>

Returns:

the value

Throws:

java.io.UncheckedIOException - if the constructor raised an IOException.

isSet

public final boolean isSet()

Is the reference set?

Returns:

true if the reference has been set.

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Object

lazyAtomicReferenceFromSupplier

public static <T> LazyAtomicReference<T> lazyAtomicReferenceFromSupplier(java.util.function.Supplier<T> supplier)

Create from a supplier. This is not a constructor to avoid ambiguity when a lambda-expression is passed in.

Type Parameters:

T - type of reference

Parameters:

supplier - supplier implementation.

Returns:

a lazy reference.