* Contains helper methods for string operations, including backported JDK functionality
 * for compatibility with older Java versions.
 */
public final class StringUtil {

    /**
     *
     */
    private StringUtil() {
    }

    /**
     * Implementation of {@link java.lang.String#join} backported for JDK7.
     *
     * @param delimiter the separator to use between elements

Rene Groeschke <******@****.***> 1622539170 +0200

   * element returned.
   *
   * <p>See <a href="https://bugs.openjdk.org/browse/JDK-6529795">JDK-6529795</a>
   */
  static class IteratorWithJdkBug6529795<T> implements Iterator<T> {
    Iterator<T> iterator;
    boolean nextThrewException;

    IteratorWithJdkBug6529795(Iterator<T> iterator) {
      this.iterator = iterator;
    }

    @Override

    should not use them for communication between trusted and untrusted code.

6.  For the mainline flavor, we test the libraries using OpenJDK 8, 11, and 17
    on Linux, with some additional testing on newer JDKs and on Windows. Some
    features, especially in `com.google.common.io`, may not work correctly in
    non-Linux environments. For the Android flavor, our unit tests also run on
    API level 23 (Marshmallow).

              <arg>-J--add-exports=jdk.compiler/com.sun.tools.javac.model=ALL-UNNAMED</arg>
              <arg>-J--add-exports=jdk.compiler/com.sun.tools.javac.parser=ALL-UNNAMED</arg>
              <arg>-J--add-exports=jdk.compiler/com.sun.tools.javac.processing=ALL-UNNAMED</arg>
              <arg>-J--add-exports=jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED</arg>
              <arg>-J--add-exports=jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED</arg>

    vararg intermediates: X509Certificate,
  ): SSLSocketFactory {
    // Test setup fails on JDK9
    // java.security.KeyStoreException: Certificate chain is not valid
    // at sun.security.pkcs12.PKCS12KeyStore.setKeyEntry
    // http://openjdk.java.net/jeps/229
    // http://hg.openjdk.java.net/jdk9/jdk9/jdk/file/2c1c21d11e58/src/share/classes/sun/security/pkcs12/PKCS12KeyStore.java#l596

  // The Kotlin compiler will parse and check module dependencies,
  // but it currently won't compile to a module-info.class file.
  // Note that module checking only works on JDK 9+,
  // because the JDK built-in base modules are not available in earlier versions.
  val javaVersion = compileKotlinTask.kotlinJavaToolchain.javaVersion.getOrNull()
  when {
    javaVersion?.isJava9Compatible == true -> {

Available JDKs on your machine are automatically detected and wired for the various compile and test tasks.
Some tests require multiple JDKs to be installed on your computer, be aware of this if you make changes related to anything toolchains related.

                InputStream jdksExtraIS =
                        MavenToolchainMergerTest.class.getResourceAsStream("toolchains-jdks-extra.xml")) {
            PersistedToolchains jdks = read(jdksIS);
            PersistedToolchains jdksExtra = read(jdksExtraIS);
            assertEquals(2, jdks.getToolchains().size());

            merger.merge(jdks, jdksExtra, TrackableBase.USER_LEVEL);

JDK 16 is required to build Elasticsearch. You must have a JDK 16 installation
with the environment variable `JAVA_HOME` referencing the path to Java home for
your JDK 16 installation. By default, tests use the same runtime as `JAVA_HOME`.
However, since Elasticsearch supports JDK 11, the build supports compiling with
JDK 16 and testing on a JDK 11 runtime; to do this, set `RUNTIME_JAVA_HOME`