Functional Interface:

This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.
```
@FunctionalInterface
public interface GatewayObserver
```
Event listeners for gateway connection lifecycle.

Field Summary

Fields
Modifier and Type	Field	Description
`static ConnectionObserver.State`	`CONNECTED`	Propagated when a gateway connection has been established.
`static ConnectionObserver.State`	`DISCONNECTED`	Propagated when a gateway connection has been fully closed.
`static ConnectionObserver.State`	`DISCONNECTED_RESUME`	Propagated when a gateway connection has been closed but is still open for a RESUME attempt.
`static GatewayObserver`	`NOOP_LISTENER`
`static ConnectionObserver.State`	`RETRY_FAILED`	Propagated when a reconnection attempt has failed.
`static ConnectionObserver.State`	`RETRY_RESUME_STARTED`	Propagated when a reconnection attempt with RESUME has started.
`static ConnectionObserver.State`	`RETRY_STARTED`	Propagated when a reconnection attempt with IDENTIFY has started.
`static ConnectionObserver.State`	`RETRY_SUCCEEDED`	Propagated when a reconnection attempt has succeeded.
`static ConnectionObserver.State`	`SEQUENCE`	Propagated when the current session sequence value has updated.

Method Summary

All Methods Static Methods Instance Methods Abstract Methods Default Methods
Modifier and Type	Method	Description
`static GatewayObserver`	`emptyListener()`
`void`	`onStateChange(ConnectionObserver.State newState, GatewayClient client)`	React on websocket state change.
`default GatewayObserver`	`then(GatewayObserver other)`	Chain together another `GatewayObserver`.

- Field Detail
  - NOOP_LISTENER
```
static final GatewayObserver NOOP_LISTENER
```
  - CONNECTED
```
static final ConnectionObserver.State CONNECTED
```
    Propagated when a gateway connection has been established.
  - DISCONNECTED
```
static final ConnectionObserver.State DISCONNECTED
```
    Propagated when a gateway connection has been fully closed.
  - DISCONNECTED_RESUME
```
static final ConnectionObserver.State DISCONNECTED_RESUME
```
    Propagated when a gateway connection has been closed but is still open for a RESUME attempt.
  - RETRY_RESUME_STARTED
```
static final ConnectionObserver.State RETRY_RESUME_STARTED
```
    Propagated when a reconnection attempt with RESUME has started.
  - RETRY_STARTED
```
static final ConnectionObserver.State RETRY_STARTED
```
    Propagated when a reconnection attempt with IDENTIFY has started.
  - RETRY_SUCCEEDED
```
static final ConnectionObserver.State RETRY_SUCCEEDED
```
    Propagated when a reconnection attempt has succeeded.
  - RETRY_FAILED
```
static final ConnectionObserver.State RETRY_FAILED
```
    Propagated when a reconnection attempt has failed.
  - SEQUENCE
```
static final ConnectionObserver.State SEQUENCE
```
    Propagated when the current session sequence value has updated.
- Method Detail
  - emptyListener
```
static GatewayObserver emptyListener()
```
  - onStateChange
```
void onStateChange(ConnectionObserver.State newState,
                   GatewayClient client)
```
    React on websocket state change.
    
    Parameters:
    
    newState - the new state
    
    client - the gateway client observing this change
  - then
```
default GatewayObserver then(GatewayObserver other)
```
    Chain together another GatewayObserver.
    
    Parameters:
    
    other - the next GatewayObserver
    
    Returns:
    
    a new composite GatewayObserver

Interface GatewayObserver

Field Summary

Method Summary

Field Detail

NOOP_LISTENER

CONNECTED

DISCONNECTED

DISCONNECTED_RESUME

RETRY_RESUME_STARTED

RETRY_STARTED

RETRY_SUCCEEDED

RETRY_FAILED

SEQUENCE

Method Detail

emptyListener

onStateChange

then