https://github.com/google/guava/guava: Guava is a suite of core and expanded libraries that include utility classes, google's collections, io classes, and much much more. 
final class com.google.common.cache.LocalCache$KeySet extends com.google.common.cache.LocalCache<K, V>.AbstractCacheSet<K>
  minor version: 0
  major version: 59
  flags: flags: (0x0030) ACC_FINAL, ACC_SUPER
  this_class: com.google.common.cache.LocalCache$KeySet
  super_class: com.google.common.cache.LocalCache$AbstractCacheSet
{
  final com.google.common.cache.LocalCache this$0;
    descriptor: Lcom/google/common/cache/LocalCache;
    flags: (0x1010) ACC_FINAL, ACC_SYNTHETIC

  void <init>(java.util.concurrent.ConcurrentMap<?, ?>);
    descriptor: (Lcom/google/common/cache/LocalCache;Ljava/util/concurrent/ConcurrentMap;)V
    flags: (0x0000) 
    Code:
      stack=3, locals=3, args_size=3
        start local 0 // com.google.common.cache.LocalCache$KeySet this
        start local 2 // java.util.concurrent.ConcurrentMap map
         0: .line 4558
            aload 0 /* this */
            aload 1
            putfield com.google.common.cache.LocalCache$KeySet.this$0:Lcom/google/common/cache/LocalCache;
         1: .line 4559
            aload 0 /* this */
            aload 1
            aload 2 /* map */
            invokespecial com.google.common.cache.LocalCache$AbstractCacheSet.<init>:(Lcom/google/common/cache/LocalCache;Ljava/util/concurrent/ConcurrentMap;)V
         2: .line 4560
            return
        end local 2 // java.util.concurrent.ConcurrentMap map
        end local 0 // com.google.common.cache.LocalCache$KeySet this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    3     0  this  Lcom/google/common/cache/LocalCache$KeySet;
            0    3     2   map  Ljava/util/concurrent/ConcurrentMap<**>;
    Signature: (Ljava/util/concurrent/ConcurrentMap<**>;)V
    MethodParameters:
        Name  Flags
      this$0  final
      map     

  public java.util.Iterator<K> iterator();
    descriptor: ()Ljava/util/Iterator;
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=3, locals=1, args_size=1
        start local 0 // com.google.common.cache.LocalCache$KeySet this
         0: .line 4564
            new com.google.common.cache.LocalCache$KeyIterator
            dup
            aload 0 /* this */
            getfield com.google.common.cache.LocalCache$KeySet.this$0:Lcom/google/common/cache/LocalCache;
            invokespecial com.google.common.cache.LocalCache$KeyIterator.<init>:(Lcom/google/common/cache/LocalCache;)V
            areturn
        end local 0 // com.google.common.cache.LocalCache$KeySet this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/common/cache/LocalCache$KeySet;
    Signature: ()Ljava/util/Iterator<TK;>;

  public boolean contains(java.lang.Object);
    descriptor: (Ljava/lang/Object;)Z
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=2, locals=2, args_size=2
        start local 0 // com.google.common.cache.LocalCache$KeySet this
        start local 1 // java.lang.Object o
         0: .line 4569
            aload 0 /* this */
            getfield com.google.common.cache.LocalCache$KeySet.map:Ljava/util/concurrent/ConcurrentMap;
            aload 1 /* o */
            invokeinterface java.util.concurrent.ConcurrentMap.containsKey:(Ljava/lang/Object;)Z
            ireturn
        end local 1 // java.lang.Object o
        end local 0 // com.google.common.cache.LocalCache$KeySet this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/common/cache/LocalCache$KeySet;
            0    1     1     o  Ljava/lang/Object;
    MethodParameters:
      Name  Flags
      o     

  public boolean remove(java.lang.Object);
    descriptor: (Ljava/lang/Object;)Z
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=2, locals=2, args_size=2
        start local 0 // com.google.common.cache.LocalCache$KeySet this
        start local 1 // java.lang.Object o
         0: .line 4574
            aload 0 /* this */
            getfield com.google.common.cache.LocalCache$KeySet.map:Ljava/util/concurrent/ConcurrentMap;
            aload 1 /* o */
            invokeinterface java.util.concurrent.ConcurrentMap.remove:(Ljava/lang/Object;)Ljava/lang/Object;
            ifnull 1
            iconst_1
            ireturn
      StackMap locals:
      StackMap stack:
         1: iconst_0
            ireturn
        end local 1 // java.lang.Object o
        end local 0 // com.google.common.cache.LocalCache$KeySet this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    2     0  this  Lcom/google/common/cache/LocalCache$KeySet;
            0    2     1     o  Ljava/lang/Object;
    MethodParameters:
      Name  Flags
      o     
}
Signature: Lcom/google/common/cache/LocalCache<TK;TV;>.AbstractCacheSet<TK;>;
SourceFile: "LocalCache.java"
NestHost: com.google.common.cache.LocalCache
InnerClasses:
  abstract AbstractCacheSet = com.google.common.cache.LocalCache$AbstractCacheSet of com.google.common.cache.LocalCache
  final KeyIterator = com.google.common.cache.LocalCache$KeyIterator of com.google.common.cache.LocalCache
  final KeySet = com.google.common.cache.LocalCache$KeySet of com.google.common.cache.LocalCache