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. 
class com.google.common.collect.Multimaps$Keys$1 extends com.google.common.collect.TransformedIterator<java.util.Map$Entry<K, java.util.Collection<V>>, com.google.common.collect.Multiset$Entry<K>>
  minor version: 0
  major version: 59
  flags: flags: (0x0020) ACC_SUPER
  this_class: com.google.common.collect.Multimaps$Keys$1
  super_class: com.google.common.collect.TransformedIterator
{
  final com.google.common.collect.Multimaps$Keys this$1;
    descriptor: Lcom/google/common/collect/Multimaps$Keys;
    flags: (0x1010) ACC_FINAL, ACC_SYNTHETIC

  void <init>(com.google.common.collect.Multimaps$Keys, java.util.Iterator);
    descriptor: (Lcom/google/common/collect/Multimaps$Keys;Ljava/util/Iterator;)V
    flags: (0x0000) 
    Code:
      stack=2, locals=3, args_size=3
        start local 0 // com.google.common.collect.Multimaps$Keys$1 this
        start local 2 // java.util.Iterator $anonymous0
         0: .line 1691
            aload 0 /* this */
            aload 1
            putfield com.google.common.collect.Multimaps$Keys$1.this$1:Lcom/google/common/collect/Multimaps$Keys;
            aload 0 /* this */
            aload 2 /* $anonymous0 */
            invokespecial com.google.common.collect.TransformedIterator.<init>:(Ljava/util/Iterator;)V
            return
        end local 2 // java.util.Iterator $anonymous0
        end local 0 // com.google.common.collect.Multimaps$Keys$1 this
      LocalVariableTable:
        Start  End  Slot         Name  Signature
            0    1     0         this  Lcom/google/common/collect/Multimaps$Keys$1;
            0    1     2  $anonymous0  Ljava/util/Iterator<+Ljava/util/Map$Entry<TK;Ljava/util/Collection<TV;>;>;>;
    MethodParameters:
             Name  Flags
      this$0       final
      $anonymous0  

  com.google.common.collect.Multiset$Entry<K> transform(java.util.Map$Entry<K, java.util.Collection<V>>);
    descriptor: (Ljava/util/Map$Entry;)Lcom/google/common/collect/Multiset$Entry;
    flags: (0x0000) 
    Code:
      stack=4, locals=2, args_size=2
        start local 0 // com.google.common.collect.Multimaps$Keys$1 this
        start local 1 // java.util.Map$Entry backingEntry
         0: .line 1695
            new com.google.common.collect.Multimaps$Keys$1$1
            dup
            aload 0 /* this */
            aload 1 /* backingEntry */
            invokespecial com.google.common.collect.Multimaps$Keys$1$1.<init>:(Lcom/google/common/collect/Multimaps$Keys$1;Ljava/util/Map$Entry;)V
            areturn
        end local 1 // java.util.Map$Entry backingEntry
        end local 0 // com.google.common.collect.Multimaps$Keys$1 this
      LocalVariableTable:
        Start  End  Slot          Name  Signature
            0    1     0          this  Lcom/google/common/collect/Multimaps$Keys$1;
            0    1     1  backingEntry  Ljava/util/Map$Entry<TK;Ljava/util/Collection<TV;>;>;
    Signature: (Ljava/util/Map$Entry<TK;Ljava/util/Collection<TV;>;>;)Lcom/google/common/collect/Multiset$Entry<TK;>;
    MethodParameters:
              Name  Flags
      backingEntry  final

  java.lang.Object transform(java.lang.Object);
    descriptor: (Ljava/lang/Object;)Ljava/lang/Object;
    flags: (0x1040) ACC_BRIDGE, ACC_SYNTHETIC
    Code:
      stack=2, locals=2, args_size=2
         0: .line 1
            aload 0
            aload 1
            checkcast java.util.Map$Entry
            invokevirtual com.google.common.collect.Multimaps$Keys$1.transform:(Ljava/util/Map$Entry;)Lcom/google/common/collect/Multiset$Entry;
            areturn
      LocalVariableTable:
        Start  End  Slot  Name  Signature
}
Signature: Lcom/google/common/collect/TransformedIterator<Ljava/util/Map$Entry<TK;Ljava/util/Collection<TV;>;>;Lcom/google/common/collect/Multiset$Entry<TK;>;>;
SourceFile: "Multimaps.java"
EnclosingMethod: com.google.common.collect.Multimaps$Keys.entryIterator:()Ljava/util/Iterator;
NestHost: com.google.common.collect.Multimaps
InnerClasses:
  Keys = com.google.common.collect.Multimaps$Keys of com.google.common.collect.Multimaps
  com.google.common.collect.Multimaps$Keys$1
  com.google.common.collect.Multimaps$Keys$1$1
  public abstract Entry = com.google.common.collect.Multiset$Entry of com.google.common.collect.Multiset
  public abstract Entry = java.util.Map$Entry of java.util.Map