https://www.graalvm.org/ 
class com.oracle.truffle.js.runtime.util.IteratorUtil$1 implements java.lang.Iterable<T>
  minor version: 0
  major version: 59
  flags: flags: (0x0020) ACC_SUPER
  this_class: com.oracle.truffle.js.runtime.util.IteratorUtil$1
  super_class: java.lang.Object
{
  private final java.lang.Iterable val$first;
    descriptor: Ljava/lang/Iterable;
    flags: (0x1012) ACC_PRIVATE, ACC_FINAL, ACC_SYNTHETIC

  private final java.lang.Iterable val$second;
    descriptor: Ljava/lang/Iterable;
    flags: (0x1012) ACC_PRIVATE, ACC_FINAL, ACC_SYNTHETIC

  void <init>(java.lang.Iterable, java.lang.Iterable);
    descriptor: (Ljava/lang/Iterable;Ljava/lang/Iterable;)V
    flags: (0x0000) 
    Code:
      stack=2, locals=3, args_size=3
        start local 0 // com.oracle.truffle.js.runtime.util.IteratorUtil$1 this
         0: .line 134
            aload 0 /* this */
            aload 1
            putfield com.oracle.truffle.js.runtime.util.IteratorUtil$1.val$first:Ljava/lang/Iterable;
            aload 0 /* this */
            aload 2
            putfield com.oracle.truffle.js.runtime.util.IteratorUtil$1.val$second:Ljava/lang/Iterable;
            aload 0 /* this */
            invokespecial java.lang.Object.<init>:()V
            return
        end local 0 // com.oracle.truffle.js.runtime.util.IteratorUtil$1 this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/oracle/truffle/js/runtime/util/IteratorUtil$1;
    MethodParameters:
            Name  Flags
      val$first   final
      val$second  final

  public java.util.Iterator<T> iterator();
    descriptor: ()Ljava/util/Iterator;
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=5, locals=1, args_size=1
        start local 0 // com.oracle.truffle.js.runtime.util.IteratorUtil$1 this
         0: .line 137
            new com.oracle.truffle.js.runtime.util.IteratorUtil$1$1
            dup
            aload 0 /* this */
            aload 0 /* this */
            getfield com.oracle.truffle.js.runtime.util.IteratorUtil$1.val$first:Ljava/lang/Iterable;
            aload 0 /* this */
            getfield com.oracle.truffle.js.runtime.util.IteratorUtil$1.val$second:Ljava/lang/Iterable;
            invokespecial com.oracle.truffle.js.runtime.util.IteratorUtil$1$1.<init>:(Lcom/oracle/truffle/js/runtime/util/IteratorUtil$1;Ljava/lang/Iterable;Ljava/lang/Iterable;)V
            areturn
        end local 0 // com.oracle.truffle.js.runtime.util.IteratorUtil$1 this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/oracle/truffle/js/runtime/util/IteratorUtil$1;
    Signature: ()Ljava/util/Iterator<TT;>;
}
Signature: Ljava/lang/Object;Ljava/lang/Iterable<TT;>;
SourceFile: "IteratorUtil.java"
EnclosingMethod: com.oracle.truffle.js.runtime.util.IteratorUtil.concatIterables:(Ljava/lang/Iterable;Ljava/lang/Iterable;)Ljava/lang/Iterable;
NestHost: com.oracle.truffle.js.runtime.util.IteratorUtil
InnerClasses:
  com.oracle.truffle.js.runtime.util.IteratorUtil$1
  com.oracle.truffle.js.runtime.util.IteratorUtil$1$1