https://github.com/Terracotta-OSS/offheap-store/: A library that offers data structures allocated off the java heap. 
public class org.terracotta.offheapstore.OffHeapHashMap$KeyIterator extends org.terracotta.offheapstore.OffHeapHashMap<K, V>.HashIterator<K>
  minor version: 0
  major version: 59
  flags: flags: (0x0021) ACC_PUBLIC, ACC_SUPER
  this_class: org.terracotta.offheapstore.OffHeapHashMap$KeyIterator
  super_class: org.terracotta.offheapstore.OffHeapHashMap$HashIterator
{
  final org.terracotta.offheapstore.OffHeapHashMap this$0;
    descriptor: Lorg/terracotta/offheapstore/OffHeapHashMap;
    flags: (0x1010) ACC_FINAL, ACC_SYNTHETIC

  void <init>(org.terracotta.offheapstore.OffHeapHashMap);
    descriptor: (Lorg/terracotta/offheapstore/OffHeapHashMap;)V
    flags: (0x0000) 
    Code:
      stack=2, locals=2, args_size=2
        start local 0 // org.terracotta.offheapstore.OffHeapHashMap$KeyIterator this
         0: .line 1511
            aload 0 /* this */
            aload 1
            putfield org.terracotta.offheapstore.OffHeapHashMap$KeyIterator.this$0:Lorg/terracotta/offheapstore/OffHeapHashMap;
         1: .line 1512
            aload 0 /* this */
            aload 1
            invokespecial org.terracotta.offheapstore.OffHeapHashMap$HashIterator.<init>:(Lorg/terracotta/offheapstore/OffHeapHashMap;)V
         2: .line 1513
            return
        end local 0 // org.terracotta.offheapstore.OffHeapHashMap$KeyIterator this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    3     0  this  Lorg/terracotta/offheapstore/OffHeapHashMap$KeyIterator;
    MethodParameters:
        Name  Flags
      this$0  final

  protected K create(java.nio.IntBuffer);
    descriptor: (Ljava/nio/IntBuffer;)Ljava/lang/Object;
    flags: (0x0004) ACC_PROTECTED
    Code:
      stack=5, locals=2, args_size=2
        start local 0 // org.terracotta.offheapstore.OffHeapHashMap$KeyIterator this
        start local 1 // java.nio.IntBuffer entry
         0: .line 1518
            aload 0 /* this */
            getfield org.terracotta.offheapstore.OffHeapHashMap$KeyIterator.this$0:Lorg/terracotta/offheapstore/OffHeapHashMap;
            getfield org.terracotta.offheapstore.OffHeapHashMap.storageEngine:Lorg/terracotta/offheapstore/storage/StorageEngine;
            aload 1 /* entry */
            iconst_2
            invokestatic org.terracotta.offheapstore.OffHeapHashMap.readLong:(Ljava/nio/IntBuffer;I)J
            aload 1 /* entry */
            iconst_1
            invokevirtual java.nio.IntBuffer.get:(I)I
            invokeinterface org.terracotta.offheapstore.storage.StorageEngine.readKey:(JI)Ljava/lang/Object;
            areturn
        end local 1 // java.nio.IntBuffer entry
        end local 0 // org.terracotta.offheapstore.OffHeapHashMap$KeyIterator this
      LocalVariableTable:
        Start  End  Slot   Name  Signature
            0    1     0   this  Lorg/terracotta/offheapstore/OffHeapHashMap$KeyIterator;
            0    1     1  entry  Ljava/nio/IntBuffer;
    Signature: (Ljava/nio/IntBuffer;)TK;
    MethodParameters:
       Name  Flags
      entry  
}
Signature: Lorg/terracotta/offheapstore/OffHeapHashMap<TK;TV;>.HashIterator<TK;>;
SourceFile: "OffHeapHashMap.java"
NestHost: org.terracotta.offheapstore.OffHeapHashMap
InnerClasses:
  protected abstract HashIterator = org.terracotta.offheapstore.OffHeapHashMap$HashIterator of org.terracotta.offheapstore.OffHeapHashMap
  protected KeyIterator = org.terracotta.offheapstore.OffHeapHashMap$KeyIterator of org.terracotta.offheapstore.OffHeapHashMap