TraceState (OpenTelemetry API)

```
@Immutable
public interface TraceState
```
Carries tracing-system specific context in a list of key-value pairs. TraceState allows different vendors propagate additional information and inter-operate with their legacy Id formats.
Implementation is optimized for a small list of key-value pairs.
Key is opaque string up to 256 characters printable. It MUST begin with a lowercase letter, and can only contain lowercase letters a-z, digits 0-9, underscores _, dashes -, asterisks *, and forward slashes /.
Value is opaque string up to 256 characters printable ASCII RFC0020 characters (i.e., the range 0x20 to 0x7E) except comma , and =.
Implementations of this interface *must* be immutable and have well-defined value-based equals/hashCode implementations. If an implementation does not strictly conform to these requirements, behavior of the OpenTelemetry APIs and default SDK cannot be guaranteed.
Implementations of this interface that do not conform to the W3C specification risk incompatibility with W3C-compatible implementations.
For these reasons, it is strongly suggested that you use the implementation that is provided here via the builder().

Method Summary

All Methods Static Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`Map<String,String>`	`asMap()`	Returns a read-only view of this `TraceState` as a `Map`.
`static TraceStateBuilder`	`builder()`	Returns an empty `TraceStateBuilder`.
`void`	`forEach(BiConsumer<String,String> consumer)`	Iterates over all the key-value entries contained in this `TraceState`.
`String`	`get(String key)`	Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.
`static TraceState`	`getDefault()`	Returns the default `TraceState` with no entries.
`boolean`	`isEmpty()`	Returns whether this `TraceState` is empty, containing no entries.
`int`	`size()`	Returns the number of entries in this `TraceState`.
`TraceStateBuilder`	`toBuilder()`	Returns a `Builder` based on this `TraceState`.

- Method Detail
  - getDefault
```
static TraceState getDefault()
```
    Returns the default TraceState with no entries.
    This method is equivalent to calling #builder().build(), but avoids new allocations.
    
    Returns:
    
    the default TraceState with no entries.
  - builder
```
static TraceStateBuilder builder()
```
    Returns an empty TraceStateBuilder.
  - get
```
@Nullable
String get(String key)
```
    Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.
    
    Parameters:
    
    key - with which the specified value is to be associated
    
    Returns:
    
    the value to which the specified key is mapped, or null if this map contains no mapping for the key.
  - size
```
int size()
```
    Returns the number of entries in this TraceState.
  - isEmpty
```
boolean isEmpty()
```
    Returns whether this TraceState is empty, containing no entries.
  - forEach
```
void forEach(BiConsumer<String,String> consumer)
```
    Iterates over all the key-value entries contained in this TraceState.
  - asMap
```
Map<String,String> asMap()
```
    Returns a read-only view of this TraceState as a Map.
  - toBuilder
```
TraceStateBuilder toBuilder()
```
    Returns a Builder based on this TraceState.
    
    Returns:
    
    a Builder based on this TraceState.