printEvent("callStart");
  }

  @Override public void callEnd(Call call) {
    printEvent("callEnd");
  }

  ...
}
```

We can use this listener to race a pair of concurrent HTTP requests:

```java
Request washingtonPostRequest = new Request.Builder()
    .url("https://www.washingtonpost.com/")
    .build();
client.newCall(washingtonPostRequest).enqueue(new Callback() {

import org.jspecify.annotations.Nullable;

/**
 * A {@code SetMultimap} whose set of values for a given key are kept sorted; that is, they comprise
 * a {@link SortedSet}. It cannot hold duplicate key-value pairs; adding a key-value pair that's
 * already in the multimap has no effect. This interface does not specify the ordering of the
 * multimap's keys. See the {@link Multimap} documentation for information common to all multimaps.
 *

				// both 1st operand and 3rd operand are (Rs, Rs+1) register pair.
				// And the register pair must be contiguous.
				if (a[0].Type != obj.TYPE_REGREG) || (a[2].Type != obj.TYPE_REGREG) {
					p.errorf("invalid addressing modes for 1st or 3rd operand to %s instruction, must be register pair", op)
					return
				}
				// For ARM64 CASP-like instructions, its 2nd destination operand is register pair(Rt, Rt+1) that can

     * Gets the query builder for this context.
     * @return The query builder.
     */
    public QueryBuilder getQueryBuilder() {
        return queryBuilder;
    }

    /**
     * Adds a field and text pair to the field log for tracking query terms.
     * @param field The field name.
     * @param text The query text for this field.
     */
    public void addFieldLog(final String field, final String text) {

    "old key": "old value",
    "second old key": "second old value",
}
new_dict = {**old_dict, "new key": "new value"}
```

Here, `new_dict` will contain all the key-value pairs from `old_dict` plus the new key-value pair:

```Python
{
    "old key": "old value",
    "second old key": "second old value",
    "new key": "new value",
}
```

private val TOKEN_DELIMITERS = "\t ,=".encodeUtf8()

/**
 * Parse RFC 7235 challenges. This is awkward because we need to look ahead to know how to
 * interpret a token.
 *
 * For example, the first line has a parameter name/value pair and the second line has a single
 * token68:
 *
 * ```
 * WWW-Authenticate: Digest foo=bar
 * WWW-Authenticate: Digest foo=
 * ```
 *

     *
     * @param css the CSS class name to match
     */
    public void setCss(final String css) {
        this.css = css;
    }

    /**
     * Sets a custom attribute name-value pair that this pruned tag should match.
     *
     * @param name the attribute name to match
     * @param value the attribute value to match
     */
    public void setAttr(final String name, final String value) {

	}
	if w.Endpoint.IsEmpty() {
		return errors.New("endpoint empty")
	}
	if w.ClientCert != "" && w.ClientKey == "" || w.ClientCert == "" && w.ClientKey != "" {
		return errors.New("cert and key must be specified as a pair")
	}
	return nil
}

// WebhookTarget - Webhook target.
type WebhookTarget struct {
	activeRequests int64
	totalRequests  int64
	failedRequests int64

	lazyInit lazyInit

import okio.Buffer
import okio.ForwardingSink
import okio.ForwardingSource
import okio.Sink
import okio.Socket
import okio.Source
import okio.buffer

/**
 * Transmits a single HTTP request and a response pair. This layers connection management and events
 * on [ExchangeCodec], which handles the actual I/O.
 */
class Exchange(
  internal val call: RealCall,
  internal val finder: ExchangeFinder,

   * input bit(i) and output bit(j), two pairs of keys must be found with all bits identical except
   * bit(i). One pair must differ in output bit(j), and one pair must not. This proves that input
   * bit(i) can alter output bit(j).
   */
  static void checkNoFunnels(HashFunction function) {
    Random rand = new Random(0);
    int keyBits = 32;