Added in [API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) Summary: [Ctors](https://developer.android.com/reference/java/util/concurrent/Exchanger#pubctors) \| [Methods](https://developer.android.com/reference/java/util/concurrent/Exchanger#pubmethods) \| [Inherited Methods](https://developer.android.com/reference/java/util/concurrent/Exchanger#inhmethods)

# Exchanger


`
public


class
Exchanger
`


`

extends https://developer.android.com/reference/java/lang/Object


`

`


`

|---|---|
| [java.lang.Object](https://developer.android.com/reference/java/lang/Object) ||
| ↳ | java.util.concurrent.Exchanger\<V\> |

<br />

*** ** * ** ***

A synchronization point at which threads can pair and swap elements
within pairs. Each thread presents some object on entry to the
`https://developer.android.com/reference/java/util/concurrent/Exchanger#exchange(V)` method, matches with a partner thread,
and receives its partner's object on return. An Exchanger may be
viewed as a bidirectional form of a `https://developer.android.com/reference/java/util/concurrent/SynchronousQueue`.
Exchangers may be useful in applications such as genetic algorithms
and pipeline designs.

**Sample Usage:**
Here are the highlights of a class that uses an `Exchanger`
to swap buffers between threads so that the thread filling the
buffer gets a freshly emptied one when it needs it, handing off the
filled one to the thread emptying the buffer.

    class FillAndEmpty {
      Exchanger<DataBuffer> exchanger = new Exchanger<>();
      DataBuffer initialEmptyBuffer = ...; // a made-up type
      DataBuffer initialFullBuffer = ...;

      class FillingLoop implements Runnable {
        public void run() {
          DataBuffer currentBuffer = initialEmptyBuffer;
          try {
            while (currentBuffer != null) {
              addToBuffer(currentBuffer);
              if (currentBuffer.isFull())
                currentBuffer = exchanger.exchange(currentBuffer);
            }
          } catch (InterruptedException ex) { ... handle ...}
        }
      }

      class EmptyingLoop implements Runnable {
        public void run() {
          DataBuffer currentBuffer = initialFullBuffer;
          try {
            while (currentBuffer != null) {
              takeFromBuffer(currentBuffer);
              if (currentBuffer.isEmpty())
                currentBuffer = exchanger.exchange(currentBuffer);
            }
          } catch (InterruptedException ex) { ... handle ...}
        }
      }

      void start() {
        new Thread(new FillingLoop()).start();
        new Thread(new EmptyingLoop()).start();
      }
    }

Memory consistency effects: For each pair of threads that
successfully exchange objects via an `Exchanger`, actions
prior to the `exchange()` in each thread
[*happen-before*](https://developer.android.com/reference/java/util/concurrent/package-summary#MemoryVisibility)
those subsequent to a return from the corresponding `exchange()`
in the other thread.

## Summary

| ### Public constructors ||
|---|---|
| ` https://developer.android.com/reference/java/util/concurrent/Exchanger#Exchanger()() ` Creates a new Exchanger. |

| ### Public methods ||
|---|---|
| ` V` | ` https://developer.android.com/reference/java/util/concurrent/Exchanger#exchange(V,%20long,%20java.util.concurrent.TimeUnit)(V x, long timeout, https://developer.android.com/reference/java/util/concurrent/TimeUnit unit) ` Waits for another thread to arrive at this exchange point (unless the current thread is [interrupted](https://developer.android.com/reference/java/lang/Thread#interrupt()) or the specified waiting time elapses), and then transfers the given object to it, receiving its object in return. |
| ` V` | ` https://developer.android.com/reference/java/util/concurrent/Exchanger#exchange(V)(V x) ` Waits for another thread to arrive at this exchange point (unless the current thread is [interrupted](https://developer.android.com/reference/java/lang/Thread#interrupt())), and then transfers the given object to it, receiving its object in return. |

| ### Inherited methods |
|---|---|
| From class ` https://developer.android.com/reference/java/lang/Object ` |---|---| | ` https://developer.android.com/reference/java/lang/Object` | ` https://developer.android.com/reference/java/lang/Object#clone()() ` Creates and returns a copy of this object. | | ` boolean` | ` https://developer.android.com/reference/java/lang/Object#equals(java.lang.Object)(https://developer.android.com/reference/java/lang/Object obj) ` Indicates whether some other object is "equal to" this one. | | ` void` | ` https://developer.android.com/reference/java/lang/Object#finalize()() ` Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. | | ` final https://developer.android.com/reference/java/lang/Class<?>` | ` https://developer.android.com/reference/java/lang/Object#getClass()() ` Returns the runtime class of this `Object`. | | ` int` | ` https://developer.android.com/reference/java/lang/Object#hashCode()() ` Returns a hash code value for the object. | | ` final void` | ` https://developer.android.com/reference/java/lang/Object#notify()() ` Wakes up a single thread that is waiting on this object's monitor. | | ` final void` | ` https://developer.android.com/reference/java/lang/Object#notifyAll()() ` Wakes up all threads that are waiting on this object's monitor. | | ` https://developer.android.com/reference/java/lang/String` | ` https://developer.android.com/reference/java/lang/Object#toString()() ` Returns a string representation of the object. | | ` final void` | ` https://developer.android.com/reference/java/lang/Object#wait(long,%20int)(long timeoutMillis, int nanos) ` Causes the current thread to wait until it is awakened, typically by being *notified* or *interrupted*, or until a certain amount of real time has elapsed. | | ` final void` | ` https://developer.android.com/reference/java/lang/Object#wait(long)(long timeoutMillis) ` Causes the current thread to wait until it is awakened, typically by being *notified* or *interrupted*, or until a certain amount of real time has elapsed. | | ` final void` | ` https://developer.android.com/reference/java/lang/Object#wait()() ` Causes the current thread to wait until it is awakened, typically by being *notified* or *interrupted*. | ||

## Public constructors

### Exchanger

Added in [API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public Exchanger ()
```

Creates a new Exchanger.

<br />

## Public methods

### exchange

Added in [API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public V exchange (V x, 
                long timeout, 
                TimeUnit unit)
```

Waits for another thread to arrive at this exchange point (unless
the current thread is [interrupted](https://developer.android.com/reference/java/lang/Thread#interrupt()) or
the specified waiting time elapses), and then transfers the given
object to it, receiving its object in return.

If another thread is already waiting at the exchange point then
it is resumed for thread scheduling purposes and receives the object
passed in by the current thread. The current thread returns immediately,
receiving the object passed to the exchange by that other thread.

If no other thread is already waiting at the exchange then the
current thread is disabled for thread scheduling purposes and lies
dormant until one of three things happens:

- Some other thread enters the exchange; or
- Some other thread [interrupts](https://developer.android.com/reference/java/lang/Thread#interrupt()) the current thread; or
- The specified waiting time elapses.

If the current thread:

- has its interrupted status set on entry to this method; or
- is [interrupted](https://developer.android.com/reference/java/lang/Thread#interrupt()) while waiting for the exchange,

then `https://developer.android.com/reference/java/lang/InterruptedException` is thrown and the current thread's interrupted status is cleared.

If the specified waiting time elapses then `https://developer.android.com/reference/java/util/concurrent/TimeoutException` is thrown. If the time is less than or equal
to zero, the method will not wait at all.

<br />

| Parameters ||
|---|---|
| `x` | `V`: the object to exchange <br /> |
| `timeout` | `long`: the maximum time to wait <br /> |
| `unit` | `TimeUnit`: the time unit of the `timeout` argument <br /> |

| Returns ||
|---|---|
| `V` | the object provided by the other thread <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/InterruptedException` | if the current thread was interrupted while waiting |
| `https://developer.android.com/reference/java/util/concurrent/TimeoutException` | if the specified waiting time elapses before another thread enters the exchange |

### exchange

Added in [API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public V exchange (V x)
```

Waits for another thread to arrive at this exchange point (unless
the current thread is [interrupted](https://developer.android.com/reference/java/lang/Thread#interrupt())),
and then transfers the given object to it, receiving its object
in return.

If another thread is already waiting at the exchange point then
it is resumed for thread scheduling purposes and receives the object
passed in by the current thread. The current thread returns immediately,
receiving the object passed to the exchange by that other thread.

If no other thread is already waiting at the exchange then the
current thread is disabled for thread scheduling purposes and lies
dormant until one of two things happens:

- Some other thread enters the exchange; or
- Some other thread [interrupts](https://developer.android.com/reference/java/lang/Thread#interrupt()) the current thread.

If the current thread:

- has its interrupted status set on entry to this method; or
- is [interrupted](https://developer.android.com/reference/java/lang/Thread#interrupt()) while waiting for the exchange,

then `https://developer.android.com/reference/java/lang/InterruptedException` is thrown and the current thread's interrupted status is cleared.

<br />

<br />

| Parameters ||
|---|---|
| `x` | `V`: the object to exchange <br /> |

| Returns ||
|---|---|
| `V` | the object provided by the other thread <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/InterruptedException` | if the current thread was interrupted while waiting |