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.collect.HashBiMap$KeySet extends com.google.common.collect.Maps$KeySet<K, V>
  minor version: 0
  major version: 59
  flags: flags: (0x0030) ACC_FINAL, ACC_SUPER
  this_class: com.google.common.collect.HashBiMap$KeySet
  super_class: com.google.common.collect.Maps$KeySet
{
  final com.google.common.collect.HashBiMap this$0;
    descriptor: Lcom/google/common/collect/HashBiMap;
    flags: (0x1010) ACC_FINAL, ACC_SYNTHETIC

  void <init>(com.google.common.collect.HashBiMap);
    descriptor: (Lcom/google/common/collect/HashBiMap;)V
    flags: (0x0000) 
    Code:
      stack=2, locals=2, args_size=2
        start local 0 // com.google.common.collect.HashBiMap$KeySet this
         0: .line 450
            aload 0 /* this */
            aload 1
            putfield com.google.common.collect.HashBiMap$KeySet.this$0:Lcom/google/common/collect/HashBiMap;
         1: .line 451
            aload 0 /* this */
            aload 1
            invokespecial com.google.common.collect.Maps$KeySet.<init>:(Ljava/util/Map;)V
         2: .line 452
            return
        end local 0 // com.google.common.collect.HashBiMap$KeySet this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    3     0  this  Lcom/google/common/collect/HashBiMap$KeySet;
    MethodParameters:
        Name  Flags
      this$0  final

  public java.util.Iterator<K> iterator();
    descriptor: ()Ljava/util/Iterator;
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=4, locals=1, args_size=1
        start local 0 // com.google.common.collect.HashBiMap$KeySet this
         0: .line 456
            new com.google.common.collect.HashBiMap$KeySet$1
            dup
            aload 0 /* this */
            aload 0 /* this */
            getfield com.google.common.collect.HashBiMap$KeySet.this$0:Lcom/google/common/collect/HashBiMap;
            invokespecial com.google.common.collect.HashBiMap$KeySet$1.<init>:(Lcom/google/common/collect/HashBiMap$KeySet;Lcom/google/common/collect/HashBiMap;)V
            areturn
        end local 0 // com.google.common.collect.HashBiMap$KeySet this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/common/collect/HashBiMap$KeySet;
    Signature: ()Ljava/util/Iterator<TK;>;

  public boolean remove(java.lang.Object);
    descriptor: (Ljava/lang/Object;)Z
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=3, locals=3, args_size=2
        start local 0 // com.google.common.collect.HashBiMap$KeySet this
        start local 1 // java.lang.Object o
         0: .line 466
            aload 0 /* this */
            getfield com.google.common.collect.HashBiMap$KeySet.this$0:Lcom/google/common/collect/HashBiMap;
            aload 1 /* o */
            aload 1 /* o */
            invokestatic com.google.common.collect.Hashing.smearedHash:(Ljava/lang/Object;)I
            invokevirtual com.google.common.collect.HashBiMap.seekByKey:(Ljava/lang/Object;I)Lcom/google/common/collect/HashBiMap$BiEntry;
            astore 2 /* entry */
        start local 2 // com.google.common.collect.HashBiMap$BiEntry entry
         1: .line 467
            aload 2 /* entry */
            ifnonnull 3
         2: .line 468
            iconst_0
            ireturn
         3: .line 470
      StackMap locals: com.google.common.collect.HashBiMap$BiEntry
      StackMap stack:
            aload 0 /* this */
            getfield com.google.common.collect.HashBiMap$KeySet.this$0:Lcom/google/common/collect/HashBiMap;
            aload 2 /* entry */
            invokevirtual com.google.common.collect.HashBiMap.delete:(Lcom/google/common/collect/HashBiMap$BiEntry;)V
         4: .line 471
            aload 2 /* entry */
            aconst_null
            putfield com.google.common.collect.HashBiMap$BiEntry.prevInKeyInsertionOrder:Lcom/google/common/collect/HashBiMap$BiEntry;
         5: .line 472
            aload 2 /* entry */
            aconst_null
            putfield com.google.common.collect.HashBiMap$BiEntry.nextInKeyInsertionOrder:Lcom/google/common/collect/HashBiMap$BiEntry;
         6: .line 473
            iconst_1
            ireturn
        end local 2 // com.google.common.collect.HashBiMap$BiEntry entry
        end local 1 // java.lang.Object o
        end local 0 // com.google.common.collect.HashBiMap$KeySet this
      LocalVariableTable:
        Start  End  Slot   Name  Signature
            0    7     0   this  Lcom/google/common/collect/HashBiMap$KeySet;
            0    7     1      o  Ljava/lang/Object;
            1    7     2  entry  Lcom/google/common/collect/HashBiMap$BiEntry<TK;TV;>;
    RuntimeVisibleTypeAnnotations: 
      METHOD_FORMAL_PARAMETER
        org.checkerframework.checker.nullness.qual.Nullable()
    MethodParameters:
      Name  Flags
      o     
}
Signature: Lcom/google/common/collect/Maps$KeySet<TK;TV;>;
SourceFile: "HashBiMap.java"
NestHost: com.google.common.collect.HashBiMap
InnerClasses:
  private final BiEntry = com.google.common.collect.HashBiMap$BiEntry of com.google.common.collect.HashBiMap
  private final KeySet = com.google.common.collect.HashBiMap$KeySet of com.google.common.collect.HashBiMap
  com.google.common.collect.HashBiMap$KeySet$1
  KeySet = com.google.common.collect.Maps$KeySet of com.google.common.collect.Maps