Added in [API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) Summary: [Constants](https://developer.android.com/reference/java/nio/channels/SelectionKey#constants) \| [Protected Ctors](https://developer.android.com/reference/java/nio/channels/SelectionKey#proctors) \| [Methods](https://developer.android.com/reference/java/nio/channels/SelectionKey#pubmethods) \| [Inherited Methods](https://developer.android.com/reference/java/nio/channels/SelectionKey#inhmethods)

# SelectionKey


`
public


abstract
class
SelectionKey
`


`

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


`

`


`

|---|---|
| [java.lang.Object](https://developer.android.com/reference/java/lang/Object) ||
| ↳ | java.nio.channels.SelectionKey |

|---|
| Known direct subclasses [AbstractSelectionKey](https://developer.android.com/reference/java/nio/channels/spi/AbstractSelectionKey) |---|---| | [AbstractSelectionKey](https://developer.android.com/reference/java/nio/channels/spi/AbstractSelectionKey) | Base implementation class for selection keys. | |

<br />

*** ** * ** ***

A token representing the registration of a `https://developer.android.com/reference/java/nio/channels/SelectableChannel` with a
`https://developer.android.com/reference/java/nio/channels/Selector`.

A selection key is created each time a channel is registered with a
selector. A key remains valid until it is *cancelled* by invoking its
`https://developer.android.com/reference/java/nio/channels/SelectionKey#cancel()` method, by closing its channel, or by closing its
selector. Cancelling a key does not immediately remove it from its
selector; it is instead added to the selector's [*cancelled-key set*](https://developer.android.com/reference/java/nio/channels/Selector#ks) for removal during the
next selection operation. The validity of a key may be tested by invoking
its `https://developer.android.com/reference/java/nio/channels/SelectionKey#isValid()` method.


A selection key contains two *operation sets* represented as
integer values. Each bit of an operation set denotes a category of
selectable operations that are supported by the key's channel.

- The *interest set* determines which operation categories will
  be tested for readiness the next time one of the selector's selection
  methods is invoked. The interest set is initialized with the value given
  when the key is created; it may later be changed via the `https://developer.android.com/reference/java/nio/channels/SelectionKey#interestOps(int)` method.

- The *ready set* identifies the operation categories for which
  the key's channel has been detected to be ready by the key's selector.
  The ready set is initialized to zero when the key is created; it may later
  be updated by the selector during a selection operation, but it cannot be
  updated directly.

That a selection key's ready set indicates that its channel is ready for
some operation category is a hint, but not a guarantee, that an operation in
such a category may be performed by a thread without causing the thread to
block. A ready set is most likely to be accurate immediately after the
completion of a selection operation. It is likely to be made inaccurate by
external events and by I/O operations that are invoked upon the
corresponding channel.

This class defines all known operation-set bits, but precisely which
bits are supported by a given channel depends upon the type of the channel.
Each subclass of `https://developer.android.com/reference/java/nio/channels/SelectableChannel` defines an `https://developer.android.com/reference/java/nio/channels/SelectableChannel#validOps()` method which returns a set
identifying just those operations that are supported by the channel. An
attempt to set or test an operation-set bit that is not supported by a key's
channel will result in an appropriate run-time exception.

It is often necessary to associate some application-specific data with a
selection key, for example an object that represents the state of a
higher-level protocol and handles readiness notifications in order to
implement that protocol. Selection keys therefore support the
*attachment* of a single arbitrary object to a key. An object can be
attached via the `https://developer.android.com/reference/java/nio/channels/SelectionKey#attach(java.lang.Object)` method and then later retrieved via
the `https://developer.android.com/reference/java/nio/channels/SelectionKey#attachment()` method.

Selection keys are safe for use by multiple concurrent threads. A
selection operation will always use the interest-set value that was current
at the moment that the operation began.

<br />

**See also:**

- `https://developer.android.com/reference/java/nio/channels/SelectableChannel`
- `https://developer.android.com/reference/java/nio/channels/Selector`

## Summary

| ### Constants ||
|---|---|
| `int` | `https://developer.android.com/reference/java/nio/channels/SelectionKey#OP_ACCEPT` Operation-set bit for socket-accept operations. |
| `int` | `https://developer.android.com/reference/java/nio/channels/SelectionKey#OP_CONNECT` Operation-set bit for socket-connect operations. |
| `int` | `https://developer.android.com/reference/java/nio/channels/SelectionKey#OP_READ` Operation-set bit for read operations. |
| `int` | `https://developer.android.com/reference/java/nio/channels/SelectionKey#OP_WRITE` Operation-set bit for write operations. |

| ### Protected constructors ||
|---|---|
| ` https://developer.android.com/reference/java/nio/channels/SelectionKey#SelectionKey()() ` Constructs an instance of this class. |

| ### Public methods ||
|---|---|
| ` final https://developer.android.com/reference/java/lang/Object` | ` https://developer.android.com/reference/java/nio/channels/SelectionKey#attach(java.lang.Object)(https://developer.android.com/reference/java/lang/Object ob) ` Attaches the given object to this key. |
| ` final https://developer.android.com/reference/java/lang/Object` | ` https://developer.android.com/reference/java/nio/channels/SelectionKey#attachment()() ` Retrieves the current attachment. |
| ` abstract void` | ` https://developer.android.com/reference/java/nio/channels/SelectionKey#cancel()() ` Requests that the registration of this key's channel with its selector be cancelled. |
| ` abstract https://developer.android.com/reference/java/nio/channels/SelectableChannel` | ` https://developer.android.com/reference/java/nio/channels/SelectionKey#channel()() ` Returns the channel for which this key was created. |
| ` abstract int` | ` https://developer.android.com/reference/java/nio/channels/SelectionKey#interestOps()() ` Retrieves this key's interest set. |
| ` abstract https://developer.android.com/reference/java/nio/channels/SelectionKey` | ` https://developer.android.com/reference/java/nio/channels/SelectionKey#interestOps(int)(int ops) ` Sets this key's interest set to the given value. |
| ` int` | ` https://developer.android.com/reference/java/nio/channels/SelectionKey#interestOpsAnd(int)(int ops) ` Atomically sets this key's interest set to the bitwise intersection ("and") of the existing interest set and the given value. |
| ` int` | ` https://developer.android.com/reference/java/nio/channels/SelectionKey#interestOpsOr(int)(int ops) ` Atomically sets this key's interest set to the bitwise union ("or") of the existing interest set and the given value. |
| ` final boolean` | ` https://developer.android.com/reference/java/nio/channels/SelectionKey#isAcceptable()() ` Tests whether this key's channel is ready to accept a new socket connection. |
| ` final boolean` | ` https://developer.android.com/reference/java/nio/channels/SelectionKey#isConnectable()() ` Tests whether this key's channel has either finished, or failed to finish, its socket-connection operation. |
| ` final boolean` | ` https://developer.android.com/reference/java/nio/channels/SelectionKey#isReadable()() ` Tests whether this key's channel is ready for reading. |
| ` abstract boolean` | ` https://developer.android.com/reference/java/nio/channels/SelectionKey#isValid()() ` Tells whether or not this key is valid. |
| ` final boolean` | ` https://developer.android.com/reference/java/nio/channels/SelectionKey#isWritable()() ` Tests whether this key's channel is ready for writing. |
| ` abstract int` | ` https://developer.android.com/reference/java/nio/channels/SelectionKey#readyOps()() ` Retrieves this key's ready-operation set. |
| ` abstract https://developer.android.com/reference/java/nio/channels/Selector` | ` https://developer.android.com/reference/java/nio/channels/SelectionKey#selector()() ` Returns the selector for which this key was created. |

| ### 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*. | ||

## Constants

### OP_ACCEPT

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

```
public static final int OP_ACCEPT
```

Operation-set bit for socket-accept operations.

Suppose that a selection key's interest set contains
`OP_ACCEPT` at the start of a [selection operation](https://developer.android.com/reference/java/nio/channels/Selector#selop). If the selector
detects that the corresponding server-socket channel is ready to accept
another connection, or has an error pending, then it will add
`OP_ACCEPT` to the key's ready set.

<br />

<br />

Constant Value:

16
(0x00000010)


### OP_CONNECT

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

```
public static final int OP_CONNECT
```

Operation-set bit for socket-connect operations.

Suppose that a selection key's interest set contains
`OP_CONNECT` at the start of a [selection operation](https://developer.android.com/reference/java/nio/channels/Selector#selop). If the selector
detects that the corresponding socket channel is ready to complete its
connection sequence, or has an error pending, then it will add
`OP_CONNECT` to the key's ready set.

<br />

<br />

Constant Value:

8
(0x00000008)


### OP_READ

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

```
public static final int OP_READ
```

Operation-set bit for read operations.

Suppose that a selection key's interest set contains
`OP_READ` at the start of a [selection operation](https://developer.android.com/reference/java/nio/channels/Selector#selop). If the selector
detects that the corresponding channel is ready for reading, has reached
end-of-stream, has been remotely shut down for further reading, or has
an error pending, then it will add `OP_READ` to the key's
ready-operation set.

<br />

<br />

Constant Value:

1
(0x00000001)


### OP_WRITE

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

```
public static final int OP_WRITE
```

Operation-set bit for write operations.

Suppose that a selection key's interest set contains
`OP_WRITE` at the start of a [selection operation](https://developer.android.com/reference/java/nio/channels/Selector#selop). If the selector
detects that the corresponding channel is ready for writing, has been
remotely shut down for further writing, or has an error pending, then it
will add `OP_WRITE` to the key's ready set.

<br />

<br />

Constant Value:

4
(0x00000004)


## Protected constructors

### SelectionKey

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

```
protected SelectionKey ()
```

Constructs an instance of this class.

<br />

## Public methods

### attach

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

```
public final Object attach (Object ob)
```

Attaches the given object to this key.

An attached object may later be retrieved via the `https://developer.android.com/reference/java/nio/channels/SelectionKey#attachment()` method. Only one object may be attached at a time; invoking
this method causes any previous attachment to be discarded. The current
attachment may be discarded by attaching `null`.

<br />

<br />

| Parameters ||
|---|---|
| `ob` | `Object`: The object to be attached; may be `null` <br /> |

| Returns ||
|---|---|
| `https://developer.android.com/reference/java/lang/Object` | The previously-attached object, if any, otherwise `null` <br /> |

### attachment

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

```
public final Object attachment ()
```

Retrieves the current attachment.

<br />

| Returns ||
|---|---|
| `https://developer.android.com/reference/java/lang/Object` | The object currently attached to this key, or `null` if there is no attachment <br /> |

### cancel

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

```
public abstract void cancel ()
```

Requests that the registration of this key's channel with its selector
be cancelled. Upon return the key will be invalid and will have been
added to its selector's cancelled-key set. The key will be removed from
all of the selector's key sets during the next selection operation.

If this key has already been cancelled then invoking this method has
no effect. Once cancelled, a key remains forever invalid.

This method may be invoked at any time. It synchronizes on the
selector's cancelled-key set, and therefore may block briefly if invoked
concurrently with a cancellation or selection operation involving the
same selector.

<br />

<br />

### channel

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

```
public abstract SelectableChannel channel ()
```

Returns the channel for which this key was created. This method will
continue to return the channel even after the key is cancelled.

<br />

| Returns ||
|---|---|
| `https://developer.android.com/reference/java/nio/channels/SelectableChannel` | This key's channel <br /> |

### interestOps

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

```
public abstract int interestOps ()
```

Retrieves this key's interest set.

It is guaranteed that the returned set will only contain operation
bits that are valid for this key's channel.

<br />

<br />

| Returns ||
|---|---|
| `int` | This key's interest set <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/nio/channels/CancelledKeyException` | If this key has been cancelled |

### interestOps

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

```
public abstract SelectionKey interestOps (int ops)
```

Sets this key's interest set to the given value.

This method may be invoked at any time. If this method is invoked
while a selection operation is in progress then it has no effect upon
that operation; the change to the key's interest set will be seen by the
next selection operation.

<br />

| Parameters ||
|---|---|
| `ops` | `int`: The new interest set <br /> |

| Returns ||
|---|---|
| `https://developer.android.com/reference/java/nio/channels/SelectionKey` | This selection key <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/IllegalArgumentException` | If a bit in the set does not correspond to an operation that is supported by this key's channel, that is, if `(ops & ~channel().validOps()) != 0` |
| `https://developer.android.com/reference/java/nio/channels/CancelledKeyException` | If this key has been cancelled |

### interestOpsAnd

Added in [API level 33](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public int interestOpsAnd (int ops)
```

Atomically sets this key's interest set to the bitwise intersection ("and")
of the existing interest set and the given value. This method is guaranteed
to be atomic with respect to other concurrent calls to this method or to
`https://developer.android.com/reference/java/nio/channels/SelectionKey#interestOpsOr(int)`.

This method may be invoked at any time. If this method is invoked
while a selection operation is in progress then it has no effect upon
that operation; the change to the key's interest set will be seen by the
next selection operation.

<br />

##### API Note:

- Unlike the `interestOps(int)` and `interestOpsOr(int)` methods, this method does not throw `IllegalArgumentException` when invoked with bits in the interest set that do not correspond to an operation that is supported by this key's channel. This is to allow operation bits in the interest set to be cleared using bitwise complement values, e.g., `interestOpsAnd(~SelectionKey.OP_READ)` will remove the `OP_READ` from the interest set without affecting other bits.

##### Implementation Requirements:

- The default implementation synchronizes on this key and invokes `interestOps()` and `interestOps(int)` to retrieve and set this key's interest set.

| Parameters ||
|---|---|
| `ops` | `int`: The interest set to apply <br /> |

| Returns ||
|---|---|
| `int` | The previous interest set <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/nio/channels/CancelledKeyException` | If this key has been cancelled |

### interestOpsOr

Added in [API level 33](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public int interestOpsOr (int ops)
```

Atomically sets this key's interest set to the bitwise union ("or") of
the existing interest set and the given value. This method is guaranteed
to be atomic with respect to other concurrent calls to this method or to
`https://developer.android.com/reference/java/nio/channels/SelectionKey#interestOpsAnd(int)`.

This method may be invoked at any time. If this method is invoked
while a selection operation is in progress then it has no effect upon
that operation; the change to the key's interest set will be seen by the
next selection operation.

<br />

##### Implementation Requirements:

- The default implementation synchronizes on this key and invokes `interestOps()` and `interestOps(int)` to retrieve and set this key's interest set.

| Parameters ||
|---|---|
| `ops` | `int`: The interest set to apply <br /> |

| Returns ||
|---|---|
| `int` | The previous interest set <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/IllegalArgumentException` | If a bit in the set does not correspond to an operation that is supported by this key's channel, that is, if `(ops & ~channel().validOps()) != 0` |
| `https://developer.android.com/reference/java/nio/channels/CancelledKeyException` | If this key has been cancelled |

### isAcceptable

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

```
public final boolean isAcceptable ()
```

Tests whether this key's channel is ready to accept a new socket
connection.

An invocation of this method of the form `k.isAcceptable()`
behaves in exactly the same way as the expression

>     k.readyOps() & OP_ACCEPT != 0

If this key's channel does not support socket-accept operations then
this method always returns `false`.

<br />

<br />

| Returns ||
|---|---|
| `boolean` | `true` if, and only if, `readyOps() & OP_ACCEPT` is nonzero <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/nio/channels/CancelledKeyException` | If this key has been cancelled |

### isConnectable

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

```
public final boolean isConnectable ()
```

Tests whether this key's channel has either finished, or failed to
finish, its socket-connection operation.

An invocation of this method of the form `k.isConnectable()`
behaves in exactly the same way as the expression

>     k.readyOps() & OP_CONNECT != 0

If this key's channel does not support socket-connect operations
then this method always returns `false`.

<br />

<br />

| Returns ||
|---|---|
| `boolean` | `true` if, and only if, `readyOps() & OP_CONNECT` is nonzero <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/nio/channels/CancelledKeyException` | If this key has been cancelled |

### isReadable

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

```
public final boolean isReadable ()
```

Tests whether this key's channel is ready for reading.

An invocation of this method of the form `k.isReadable()`
behaves in exactly the same way as the expression

>     k.readyOps() & OP_READ != 0

If this key's channel does not support read operations then this
method always returns `false`.

<br />

<br />

| Returns ||
|---|---|
| `boolean` | `true` if, and only if, `readyOps() & OP_READ` is nonzero <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/nio/channels/CancelledKeyException` | If this key has been cancelled |

### isValid

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

```
public abstract boolean isValid ()
```

Tells whether or not this key is valid.

A key is valid upon creation and remains so until it is cancelled,
its channel is closed, or its selector is closed.

<br />

<br />

| Returns ||
|---|---|
| `boolean` | `true` if, and only if, this key is valid <br /> |

### isWritable

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

```
public final boolean isWritable ()
```

Tests whether this key's channel is ready for writing.

An invocation of this method of the form `k.isWritable()`
behaves in exactly the same way as the expression

>     k.readyOps() & OP_WRITE != 0

If this key's channel does not support write operations then this
method always returns `false`.

<br />

<br />

| Returns ||
|---|---|
| `boolean` | `true` if, and only if, `readyOps() & OP_WRITE` is nonzero <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/nio/channels/CancelledKeyException` | If this key has been cancelled |

### readyOps

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

```
public abstract int readyOps ()
```

Retrieves this key's ready-operation set.

It is guaranteed that the returned set will only contain operation
bits that are valid for this key's channel.

<br />

<br />

| Returns ||
|---|---|
| `int` | This key's ready-operation set <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/nio/channels/CancelledKeyException` | If this key has been cancelled |

### selector

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

```
public abstract Selector selector ()
```

Returns the selector for which this key was created. This method will
continue to return the selector even after the key is cancelled.

<br />

| Returns ||
|---|---|
| `https://developer.android.com/reference/java/nio/channels/Selector` | This key's selector <br /> |