* @since 18.0 (since 3.0 as {@code Objects.firstNonNull()}).
   */
  public static <T> T firstNonNull(@Nullable T first, @Nullable T second) {
    if (first != null) {
      return first;
    }
    if (second != null) {
      return second;
    }
    throw new NullPointerException("Both parameters are null");
  }

  /**
   * Creates an instance of {@link ToStringHelper}.
   *

            ImmutableSet.of(
                // DurationSpec.of(500, MILLISECONDS),
                DurationSpec.of(1, SECONDS), DurationSpec.of(1, DAYS)))
        .withExpireAfterAccesses(
            ImmutableSet.of(
                // DurationSpec.of(500, MILLISECONDS),
                DurationSpec.of(1, SECONDS), DurationSpec.of(1, DAYS)))
        .withRefreshes(
            ImmutableSet.of(

    builder.addEscape(' ', "-");
    builder.addEscape('!', "$");
    Escaper second = builder.build();
    // This should have no effect on existing escapers.
    builder.addEscape(' ', "*");

    // Test both escapers after modifying the builder.
    assertThat(first.escape("The Quick Brown Fox!")).isEqualTo("Xhe_Xuick_Xrown_XoxX");
    assertThat(second.escape("The Quick Brown Fox!")).isEqualTo("Xhe-Xuick-Xrown-Xox$");
  }

    entry = cacheEntry1;
    if (entry != null && entry.key == key) {
      return entry.value;
    }
    entry = cacheEntry2;
    if (entry != null && entry.key == key) {
      // Promote second cache entry to first so the access pattern
      // [K1, K2, K1, K3, K1, K4...] still hits the cache half the time.
      addToCache(entry);
      return entry.value;
    }
    return null;
  }

  @Override

import static java.util.concurrent.Executors.newCachedThreadPool;
import static java.util.concurrent.Executors.newSingleThreadExecutor;
import static java.util.concurrent.TimeUnit.MILLISECONDS;
import static java.util.concurrent.TimeUnit.SECONDS;
import static org.junit.Assert.assertThrows;

import com.google.common.annotations.GwtIncompatible;
import com.google.common.util.concurrent.ListenableFuture;
import java.util.concurrent.CancellationException;

  @CanIgnoreReturnValue
  public final <A extends Appendable> A appendTo(
      A appendable, @Nullable Object first, @Nullable Object second, @Nullable Object... rest)
      throws IOException {
    return appendTo(appendable, iterable(first, second, rest));
  }

  /**
   * Appends the string representation of each of {@code parts}, using the previously configured

import static com.google.common.cache.TestingCacheLoaders.identityLoader;
import static com.google.common.truth.Truth.assertThat;
import static java.util.concurrent.TimeUnit.SECONDS;

import com.google.common.cache.LocalCache.LocalLoadingCache;
import com.google.common.cache.LocalCache.Segment;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;

        }
    }

    /**
     * Validates integer for safe arithmetic operations
     *
     * @param a first operand
     * @param b second operand
     * @param operation the operation name
     * @throws ArithmeticException if operation would overflow
     */
    public static void validateIntegerAddition(int a, int b, String operation) {

    public void setCookieDomain(final String cookieDomain) {
        this.cookieDomain = cookieDomain;
    }

    /**
     * Sets the maximum age of the user identification cookie in seconds.
     *
     * @param cookieMaxAge the maximum age in seconds
     */
    public void setCookieMaxAge(final int cookieMaxAge) {
        this.cookieMaxAge = cookieMaxAge;
    }

    /**

                        endLatch.countDown();
                    }
                }
            });
        }

        startLatch.countDown();
        boolean completed = endLatch.await(30, TimeUnit.SECONDS);
        assertTrue("Test should complete within timeout", completed);
        executor.shutdown();

        assertEquals(threadCount * operationsPerThread * 2, successCount.get());