## com.google.common.util.concurrent
Class Futures

    java.lang.Object
      com.google.common.util.concurrent.Futures

    @Beta
    public final class Futures

extends Object

Static utility methods pertaining to the `Future` interface.

Many of these methods use the `ListenableFuture` API; consult the Guava User Guide article on `ListenableFuture`.

Since:
  1.0
Author:
  Kevin Bourrillion, Nishant Thakkar, Sven Mawson

Method Summary

`static

`<V> void`

`

`addCallback(ListenableFuture<V> future, FutureCallback<? super V> callback)`
Registers separate success and failure callbacks to be run when the `Future`'s computation is complete or, if the computation is already complete, immediately.

`static

`<V> void`

`

`addCallback(ListenableFuture<V> future, FutureCallback<? super V> callback, Executor executor)`
Registers separate success and failure callbacks to be run when the `Future`'s computation is complete or, if the computation is already complete, immediately.

`static

`<V> ListenableFuture<List<V>>`

`

`allAsList(Iterable<? extends ListenableFuture<? extends V>> futures)`
Creates a new `ListenableFuture` whose value is a list containing the values of all its input futures, if all succeed.

`static

`<V> ListenableFuture<List<V>>`

`

`allAsList(ListenableFuture<? extends V>... futures)`
Creates a new `ListenableFuture` whose value is a list containing the values of all its input futures, if all succeed.

`static

`<V> ListenableFuture<V>`

`

`dereference(ListenableFuture<? extends ListenableFuture<? extends V>> nested)`
Returns a new `ListenableFuture` whose result is the product of calling `get()` on the `Future` nested within the given `Future`, effectively chaining the futures one after the other.

`static

`<V,X extends Exception> V`

`

`get(Future<V> future, Class<X> exceptionClass)`
Returns the result of `Future.get()`, converting most exceptions to a new instance of the given checked exception type.

`static

`<V,X extends Exception> V`

`

`get(Future<V> future, long timeout, TimeUnit unit, Class<X> exceptionClass)`
Returns the result of `Future.get(long, TimeUnit)`, converting most exceptions to a new instance of the given checked exception type.

`static

`<V> V`

`

`getUnchecked(Future<V> future)`
Returns the result of calling `Future.get()` uninterruptibly on a task known not to throw a checked exception.

`static

`<V,X extends Exception> CheckedFuture<V,X>`

`

`immediateCheckedFuture(V value)`
Returns a `CheckedFuture` which has its value set immediately upon construction.

`static

`<V,X extends Exception> CheckedFuture<V,X>`

`

`immediateFailedCheckedFuture(X exception)`
Returns a `CheckedFuture` which has an exception set immediately upon construction.

`static

`<V> ListenableFuture<V>`

`

`immediateFailedFuture(Throwable throwable)`
Returns a `ListenableFuture` which has an exception set immediately upon construction.

`static

`<V> ListenableFuture<V>`

`

`immediateFuture(V value)`
Creates a `ListenableFuture` which has its value set immediately upon construction.

`static

`<I,O> Future<O>`

`

`lazyTransform(Future<I> input, Function<? super I,? extends O> function)`
Like `transform(ListenableFuture, Function)` except that the transformation `function` is invoked on each call to `get()` on the returned future.

`static

`<V,X extends Exception> CheckedFuture<V,X>`

`

`makeChecked(ListenableFuture<V> future, Function<Exception,X> mapper)`
Creates a `CheckedFuture` out of a normal `ListenableFuture` and a `Function` that maps from `Exception` instances into the appropriate checked type.

`static

`<V> ListenableFuture<List<V>>`

`

`successfulAsList(Iterable<? extends ListenableFuture<? extends V>> futures)`
Creates a new `ListenableFuture` whose value is a list containing the values of all its successful input futures.

`static

`<V> ListenableFuture<List<V>>`

`

`successfulAsList(ListenableFuture<? extends V>... futures)`
Creates a new `ListenableFuture` whose value is a list containing the values of all its successful input futures.

`static

`<I,O> ListenableFuture<O>`

`

`transform(ListenableFuture<I> input, AsyncFunction<? super I,? extends O> function)`
Returns a new `ListenableFuture` whose result is asynchronously derived from the result of the given `Future`.

`static

`<I,O> ListenableFuture<O>`

`

`transform(ListenableFuture<I> input, AsyncFunction<? super I,? extends O> function, Executor executor)`
Returns a new `ListenableFuture` whose result is asynchronously derived from the result of the given `Future`.

`static

`<I,O> ListenableFuture<O>`

`

`transform(ListenableFuture<I> input, Function<? super I,? extends O> function)`
Returns a new `ListenableFuture` whose result is the product of applying the given `Function` to the result of the given `Future`.

`static

`<I,O> ListenableFuture<O>`

`

`transform(ListenableFuture<I> input, Function<? super I,? extends O> function, Executor executor)`
Returns a new `ListenableFuture` whose result is the product of applying the given `Function` to the result of the given `Future`.

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Method Detail

### makeChecked

    public static <V,X extends Exception> CheckedFuture<V,X> makeChecked(ListenableFuture<V> future,
                                                                         Function<Exception,X> mapper)

  Creates a `CheckedFuture` out of a normal `ListenableFuture` and a `Function` that maps from `Exception` instances into the appropriate checked type.

  The given mapping function will be applied to an `InterruptedException`, a `CancellationException`, or an `ExecutionException` with the actual cause of the exception. See `Future.get()` for details on the exceptions thrown.

  Since:
    9.0 (source-compatible since 1.0)

### immediateFuture

    public static <V> ListenableFuture<V> immediateFuture(@Nullable
                                                          V value)

  Creates a `ListenableFuture` which has its value set immediately upon construction. The getters just return the value. This `Future` can't be canceled or timed out and its `isDone()` method always returns `true`.

### immediateCheckedFuture

    public static <V,X extends Exception> CheckedFuture<V,X> immediateCheckedFuture(@Nullable
                                                                                    V value)

  Returns a `CheckedFuture` which has its value set immediately upon construction.

  The returned `Future` can't be cancelled, and its `isDone()` method always returns `true`. Calling `get()` or `checkedGet()` will immediately return the provided value.

### immediateFailedFuture

    public static <V> ListenableFuture<V> immediateFailedFuture(Throwable throwable)

  Returns a `ListenableFuture` which has an exception set immediately upon construction.

  The returned `Future` can't be cancelled, and its `isDone()` method always returns `true`. Calling `get()` will immediately throw the provided `Throwable` wrapped in an `ExecutionException`.

  Throws:
    `Error` - if the throwable is an `Error`.

### immediateFailedCheckedFuture

    public static <V,X extends Exception> CheckedFuture<V,X> immediateFailedCheckedFuture(X exception)

  Returns a `CheckedFuture` which has an exception set immediately upon construction.

  The returned `Future` can't be cancelled, and its `isDone()` method always returns `true`. Calling `get()` will immediately throw the provided `Throwable` wrapped in an `ExecutionException`, and calling `checkedGet()` will throw the provided exception itself.

  Throws:
    `Error` - if the throwable is an `Error`.

### transform

    public static <I,O> ListenableFuture<O> transform(ListenableFuture<I> input,
                                                      AsyncFunction<? super I,? extends O> function)

  Returns a new `ListenableFuture` whose result is asynchronously derived from the result of the given `Future`. More precisely, the returned `Future` takes its result from a `Future` produced by applying the given `AsyncFunction` to the result of the original `Future`. Example:

         ListenableFuture<RowKey> rowKeyFuture = indexService.lookUp(query);
         AsyncFunction<RowKey, QueryResult> queryFunction =
             new AsyncFunction<RowKey, QueryResult>() {
               public ListenableFuture<QueryResult> apply(RowKey rowKey) {
                 return dataService.read(rowKey);
               }
             };
         ListenableFuture<QueryResult> queryFuture =
             transform(rowKeyFuture, queryFunction);

  Note: If the derived `Future` is slow or heavyweight to create (whether the `Future` itself is slow or heavyweight to complete is irrelevant), consider supplying an executor. If you do not supply an executor, `transform` will use `sameThreadExecutor`, which carries some caveats for heavier operations. For example, the call to `function.apply` may run on an unpredictable or undesirable thread:
  - If the input `Future` is done at the time `transform` is called, `transform` will call `function.apply` inline.
  - If the input `Future` is not yet done, `transform` will schedule `function.apply` to be run by the thread that completes the input `Future`, which may be an internal system thread such as an RPC network thread.
  Also note that, regardless of which thread executes `function.apply`, all other registered but unexecuted listeners are prevented from running during its execution, even if those listeners are to run in other executors.

  The returned `Future` attempts to keep its cancellation state in sync with that of the input future and that of the future returned by the function. That is, if the returned `Future` is cancelled, it will attempt to cancel the other two, and if either of the other two is cancelled, the returned `Future` will receive a callback in which it will attempt to cancel itself.

  Parameters:
    `input` - The future to transform
    `function` - A function to transform the result of the input future to the result of the output future
  Returns:
    A future that holds result of the function (if the input succeeded) or the original input's failure (if not)
  Since:
    11.0

### transform

    public static <I,O> ListenableFuture<O> transform(ListenableFuture<I> input,
                                                      AsyncFunction<? super I,? extends O> function,
                                                      Executor executor)

  Returns a new `ListenableFuture` whose result is asynchronously derived from the result of the given `Future`. More precisely, the returned `Future` takes its result from a `Future` produced by applying the given `AsyncFunction` to the result of the original `Future`. Example:

         ListenableFuture<RowKey> rowKeyFuture = indexService.lookUp(query);
         AsyncFunction<RowKey, QueryResult> queryFunction =
             new AsyncFunction<RowKey, QueryResult>() {
               public ListenableFuture<QueryResult> apply(RowKey rowKey) {
                 return dataService.read(rowKey);
               }
             };
         ListenableFuture<QueryResult> queryFuture =
             transform(rowKeyFuture, queryFunction, executor);

  The returned `Future` attempts to keep its cancellation state in sync with that of the input future and that of the future returned by the chain function. That is, if the returned `Future` is cancelled, it will attempt to cancel the other two, and if either of the other two is cancelled, the returned `Future` will receive a callback in which it will attempt to cancel itself.

  When the execution of `function.apply` is fast and lightweight (though the `Future` it returns need not meet these criteria), consider omitting the executor or explicitly specifying `sameThreadExecutor`. However, be aware of the caveats documented in the link above.

  Parameters:
    `input` - The future to transform
    `function` - A function to transform the result of the input future to the result of the output future
    `executor` - Executor to run the function in.
  Returns:
    A future that holds result of the function (if the input succeeded) or the original input's failure (if not)
  Since:
    11.0

### transform

    public static <I,O> ListenableFuture<O> transform(ListenableFuture<I> input,
                                                      Function<? super I,? extends O> function)

  Returns a new `ListenableFuture` whose result is the product of applying the given `Function` to the result of the given `Future`. Example:

         ListenableFuture<QueryResult> queryFuture = ...;
         Function<QueryResult, List<Row>> rowsFunction =
             new Function<QueryResult, List<Row>>() {
               public List<Row> apply(QueryResult queryResult) {
                 return queryResult.getRows();
               }
             };
         ListenableFuture<List<Row>> rowsFuture =
             transform(queryFuture, rowsFunction);

  Note: If the transformation is slow or heavyweight, consider supplying an executor. If you do not supply an executor, `transform` will use `sameThreadExecutor`, which carries some caveats for heavier operations. For example, the call to `function.apply` may run on an unpredictable or undesirable thread:
  - If the input `Future` is done at the time `transform` is called, `transform` will call `function.apply` inline.
  - If the input `Future` is not yet done, `transform` will schedule `function.apply` to be run by the thread that completes the input `Future`, which may be an internal system thread such as an RPC network thread.
  Also note that, regardless of which thread executes `function.apply`, all other registered but unexecuted listeners are prevented from running during its execution, even if those listeners are to run in other executors.

  The returned `Future` attempts to keep its cancellation state in sync with that of the input future. That is, if the returned `Future` is cancelled, it will attempt to cancel the input, and if the input is cancelled, the returned `Future` will receive a callback in which it will attempt to cancel itself.

  An example use of this method is to convert a serializable object returned from an RPC into a POJO.

  Parameters:
    `input` - The future to transform
    `function` - A Function to transform the results of the provided future to the results of the returned future. This will be run in the thread that notifies input it is complete.
  Returns:
    A future that holds result of the transformation.
  Since:
    9.0 (in 1.0 as `compose`)

### transform

    public static <I,O> ListenableFuture<O> transform(ListenableFuture<I> input,
                                                      Function<? super I,? extends O> function,
                                                      Executor executor)

  Returns a new `ListenableFuture` whose result is the product of applying the given `Function` to the result of the given `Future`. Example:

         ListenableFuture<QueryResult> queryFuture = ...;
         Function<QueryResult, List<Row>> rowsFunction =
             new Function<QueryResult, List<Row>>() {
               public List<Row> apply(QueryResult queryResult) {
                 return queryResult.getRows();
               }
             };
         ListenableFuture<List<Row>> rowsFuture =
             transform(queryFuture, rowsFunction, executor);

  The returned `Future` attempts to keep its cancellation state in sync with that of the input future. That is, if the returned `Future` is cancelled, it will attempt to cancel the input, and if the input is cancelled, the returned `Future` will receive a callback in which it will attempt to cancel itself.

  An example use of this method is to convert a serializable object returned from an RPC into a POJO.

  When the transformation is fast and lightweight, consider omitting the executor or explicitly specifying `sameThreadExecutor`. However, be aware of the caveats documented in the link above.

  Parameters:
    `input` - The future to transform
    `function` - A Function to transform the results of the provided future to the results of the returned future.
    `executor` - Executor to run the function in.
  Returns:
    A future that holds result of the transformation.
  Since:
    9.0 (in 2.0 as `compose`)

### lazyTransform

    @Beta
    public static <I,O> Future<O> lazyTransform(Future<I> input,
                                                     Function<? super I,? extends O> function)

  Like `transform(ListenableFuture, Function)` except that the transformation `function` is invoked on each call to `get()` on the returned future.

  The returned `Future` reflects the input's cancellation state directly, and any attempt to cancel the returned Future is likewise passed through to the input Future.

  Note that calls to timed get only apply the timeout to the execution of the underlying `Future`, not to the execution of the transformation function.

  The primary audience of this method is callers of `transform` who don't have a `ListenableFuture` available and do not mind repeated, lazy function evaluation.

  Parameters:
    `input` - The future to transform
    `function` - A Function to transform the results of the provided future to the results of the returned future.
  Returns:
    A future that returns the result of the transformation.
  Since:
    10.0

### dereference

    @Beta
    public static <V> ListenableFuture<V> dereference(ListenableFuture<? extends ListenableFuture<? extends V>> nested)

  Returns a new `ListenableFuture` whose result is the product of calling `get()` on the `Future` nested within the given `Future`, effectively chaining the futures one after the other. Example:

         SettableFuture<ListenableFuture<String>> nested = SettableFuture.create();
         ListenableFuture<String> dereferenced = dereference(nested);

  This call has the same cancellation and execution semantics as `transform(ListenableFuture, AsyncFunction)`, in that the returned `Future` attempts to keep its cancellation state in sync with both the input `Future` and the nested `Future`. The transformation is very lightweight and therefore takes place in the thread that called `dereference`.

  Parameters:
    `nested` - The nested future to transform.
  Returns:
    A future that holds result of the inner future.
  Since:
    13.0

### allAsList

    @Beta
    public static <V> ListenableFuture<List<V>> allAsList(ListenableFuture<? extends V>... futures)

  Creates a new `ListenableFuture` whose value is a list containing the values of all its input futures, if all succeed. If any input fails, the returned future fails.

  The list of results is in the same order as the input list.

  Canceling this future does not cancel any of the component futures; however, if any of the provided futures fails or is canceled, this one is, too.

  Parameters:
    `futures` - futures to combine
  Returns:
    a future that provides a list of the results of the component futures
  Since:
    10.0

### allAsList

    @Beta
    public static <V> ListenableFuture<List<V>> allAsList(Iterable<? extends ListenableFuture<? extends V>> futures)

  Creates a new `ListenableFuture` whose value is a list containing the values of all its input futures, if all succeed. If any input fails, the returned future fails.

  The list of results is in the same order as the input list.

  Canceling this future does not cancel any of the component futures; however, if any of the provided futures fails or is canceled, this one is, too.

  Parameters:
    `futures` - futures to combine
  Returns:
    a future that provides a list of the results of the component futures
  Since:
    10.0

### successfulAsList

    @Beta
    public static <V> ListenableFuture<List<V>> successfulAsList(ListenableFuture<? extends V>... futures)

  Creates a new `ListenableFuture` whose value is a list containing the values of all its successful input futures. The list of results is in the same order as the input list, and if any of the provided futures fails or is canceled, its corresponding position will contain `null` (which is indistinguishable from the future having a successful value of `null`).

  Parameters:
    `futures` - futures to combine
  Returns:
    a future that provides a list of the results of the component futures
  Since:
    10.0

### successfulAsList

    @Beta
    public static <V> ListenableFuture<List<V>> successfulAsList(Iterable<? extends ListenableFuture<? extends V>> futures)

  Creates a new `ListenableFuture` whose value is a list containing the values of all its successful input futures. The list of results is in the same order as the input list, and if any of the provided futures fails or is canceled, its corresponding position will contain `null` (which is indistinguishable from the future having a successful value of `null`).

  Parameters:
    `futures` - futures to combine
  Returns:
    a future that provides a list of the results of the component futures
  Since:
    10.0

### addCallback

    public static <V> void addCallback(ListenableFuture<V> future,
                                       FutureCallback<? super V> callback)

  Registers separate success and failure callbacks to be run when the `Future`'s computation is complete or, if the computation is already complete, immediately.

  There is no guaranteed ordering of execution of callbacks, but any callback added through this method is guaranteed to be called once the computation is complete. Example:

       ListenableFuture<QueryResult> future = ...;
       addCallback(future,
           new FutureCallback<QueryResult> {
             public void onSuccess(QueryResult result) {
               storeInCache(result);
             }
             public void onFailure(Throwable t) {
               reportError(t);
             }
           });

  Note: If the callback is slow or heavyweight, consider supplying an executor. If you do not supply an executor, `addCallback` will use `sameThreadExecutor`, which carries some caveats for heavier operations. For example, the callback may run on an unpredictable or undesirable thread:
  - If the input `Future` is done at the time `addCallback` is called, `addCallback` will execute the callback inline.
  - If the input `Future` is not yet done, `addCallback` will schedule the callback to be run by the thread that completes the input `Future`, which may be an internal system thread such as an RPC network thread.
  Also note that, regardless of which thread executes the callback, all other registered but unexecuted listeners are prevented from running during its execution, even if those listeners are to run in other executors.

  For a more general interface to attach a completion listener to a `Future`, see `addListener`.

  Parameters:
    `future` - The future attach the callback to.
    `callback` - The callback to invoke when `future` is completed.
  Since:
    10.0

### addCallback

    public static <V> void addCallback(ListenableFuture<V> future,
                                       FutureCallback<? super V> callback,
                                       Executor executor)

  Registers separate success and failure callbacks to be run when the `Future`'s computation is complete or, if the computation is already complete, immediately.

  The callback is run in `executor`. There is no guaranteed ordering of execution of callbacks, but any callback added through this method is guaranteed to be called once the computation is complete. Example:

       ListenableFuture<QueryResult> future = ...;
       Executor e = ...
       addCallback(future, e,
           new FutureCallback<QueryResult> {
             public void onSuccess(QueryResult result) {
               storeInCache(result);
             }
             public void onFailure(Throwable t) {
               reportError(t);
             }
           });

  When the callback is fast and lightweight, consider omitting the executor or explicitly specifying `sameThreadExecutor`. However, be aware of the caveats documented in the link above.

  For a more general interface to attach a completion listener to a `Future`, see `addListener`.

  Parameters:
    `future` - The future attach the callback to.
    `callback` - The callback to invoke when `future` is completed.
    `executor` - The executor to run `callback` when the future completes.
  Since:
    10.0

### get

    @Beta
    public static <V,X extends Exception> V get(Future<V> future,
                                                     Class<X> exceptionClass)
                 throws X extends Exception

  Returns the result of `Future.get()`, converting most exceptions to a new instance of the given checked exception type. This reduces boilerplate for a common use of `Future` in which it is unnecessary to programmatically distinguish between exception types or to extract other information from the exception instance.

  Exceptions from `Future.get` are treated as follows:

  - Any `ExecutionException` has its cause wrapped in an `X` if the cause is a checked exception, an `UncheckedExecutionException` if the cause is a `RuntimeException`, or an `ExecutionError` if the cause is an `Error`.
  - Any `InterruptedException` is wrapped in an `X` (after restoring the interrupt).
  - Any `CancellationException` is propagated untouched, as is any other `RuntimeException` (though `get` implementations are discouraged from throwing such exceptions).
  The overall principle is to continue to treat every checked exception as a checked exception, every unchecked exception as an unchecked exception, and every error as an error. In addition, the cause of any `ExecutionException` is wrapped in order to ensure that the new stack trace matches that of the current thread.

  Instances of `exceptionClass` are created by choosing an arbitrary public constructor that accepts zero or more arguments, all of type `String` or `Throwable` (preferring constructors with at least one `String`) and calling the constructor via reflection. If the exception did not already have a cause, one is set by calling `Throwable.initCause(Throwable)` on it. If no such constructor exists, an `IllegalArgumentException` is thrown.

  Throws:
    `X` - if `get` throws any checked exception except for an `ExecutionException` whose cause is not itself a checked exception
    `UncheckedExecutionException` - if `get` throws an `ExecutionException` with a `RuntimeException` as its cause
    `ExecutionError` - if `get` throws an `ExecutionException` with an `Error` as its cause
    `CancellationException` - if `get` throws a `CancellationException`
    `IllegalArgumentException` - if `exceptionClass` extends `RuntimeException` or does not have a suitable constructor
    `X extends Exception`
  Since:
    10.0

### get

    @Beta
    public static <V,X extends Exception> V get(Future<V> future,
                                                     long timeout,
                                                     TimeUnit unit,
                                                     Class<X> exceptionClass)
                 throws X extends Exception

  Returns the result of `Future.get(long, TimeUnit)`, converting most exceptions to a new instance of the given checked exception type. This reduces boilerplate for a common use of `Future` in which it is unnecessary to programmatically distinguish between exception types or to extract other information from the exception instance.

  Exceptions from `Future.get` are treated as follows:

  - Any `ExecutionException` has its cause wrapped in an `X` if the cause is a checked exception, an `UncheckedExecutionException` if the cause is a `RuntimeException`, or an `ExecutionError` if the cause is an `Error`.
  - Any `InterruptedException` is wrapped in an `X` (after restoring the interrupt).
  - Any `TimeoutException` is wrapped in an `X`.
  - Any `CancellationException` is propagated untouched, as is any other `RuntimeException` (though `get` implementations are discouraged from throwing such exceptions).
  The overall principle is to continue to treat every checked exception as a checked exception, every unchecked exception as an unchecked exception, and every error as an error. In addition, the cause of any `ExecutionException` is wrapped in order to ensure that the new stack trace matches that of the current thread.

  Instances of `exceptionClass` are created by choosing an arbitrary public constructor that accepts zero or more arguments, all of type `String` or `Throwable` (preferring constructors with at least one `String`) and calling the constructor via reflection. If the exception did not already have a cause, one is set by calling `Throwable.initCause(Throwable)` on it. If no such constructor exists, an `IllegalArgumentException` is thrown.

  Throws:
    `X` - if `get` throws any checked exception except for an `ExecutionException` whose cause is not itself a checked exception
    `UncheckedExecutionException` - if `get` throws an `ExecutionException` with a `RuntimeException` as its cause
    `ExecutionError` - if `get` throws an `ExecutionException` with an `Error` as its cause
    `CancellationException` - if `get` throws a `CancellationException`
    `IllegalArgumentException` - if `exceptionClass` extends `RuntimeException` or does not have a suitable constructor
    `X extends Exception`
  Since:
    10.0

### getUnchecked

    @Beta
    public static <V> V getUnchecked(Future<V> future)

  Returns the result of calling `Future.get()` uninterruptibly on a task known not to throw a checked exception. This makes `Future` more suitable for lightweight, fast-running tasks that, barring bugs in the code, will not fail. This gives it exception-handling behavior similar to that of `ForkJoinTask.join`.

  Exceptions from `Future.get` are treated as follows:

  - Any `ExecutionException` has its cause wrapped in an `UncheckedExecutionException` (if the cause is an `Exception`) or `ExecutionError` (if the cause is an `Error`).
  - Any `InterruptedException` causes a retry of the `get` call. The interrupt is restored before `getUnchecked` returns.
  - Any `CancellationException` is propagated untouched. So is any other `RuntimeException` (`get` implementations are discouraged from throwing such exceptions).
  The overall principle is to eliminate all checked exceptions: to loop to avoid `InterruptedException`, to pass through `CancellationException`, and to wrap any exception from the underlying computation in an `UncheckedExecutionException` or `ExecutionError`.

  For an uninterruptible `get` that preserves other exceptions, see `Uninterruptibles.getUninterruptibly(Future)`.

  Throws:
    `UncheckedExecutionException` - if `get` throws an `ExecutionException` with an `Exception` as its cause
    `ExecutionError` - if `get` throws an `ExecutionException` with an `Error` as its cause
    `CancellationException` - if `get` throws a `CancellationException`
  Since:
    10.0

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