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.Maps$1 extends com.google.common.collect.TransformedIterator<java.util.Map$Entry<K, V>, K>
  minor version: 0
  major version: 59
  flags: flags: (0x0020) ACC_SUPER
  this_class: com.google.common.collect.Maps$1
  super_class: com.google.common.collect.TransformedIterator
{
  void <init>(java.util.Iterator);
    descriptor: (Ljava/util/Iterator;)V
    flags: (0x0000) 
    Code:
      stack=2, locals=2, args_size=2
        start local 0 // com.google.common.collect.Maps$1 this
        start local 1 // java.util.Iterator $anonymous0
         0: .line 117
            aload 0 /* this */
            aload 1 /* $anonymous0 */
            invokespecial com.google.common.collect.TransformedIterator.<init>:(Ljava/util/Iterator;)V
            return
        end local 1 // java.util.Iterator $anonymous0
        end local 0 // com.google.common.collect.Maps$1 this
      LocalVariableTable:
        Start  End  Slot         Name  Signature
            0    1     0         this  Lcom/google/common/collect/Maps$1;
            0    1     1  $anonymous0  Ljava/util/Iterator<+Ljava/util/Map$Entry<TK;TV;>;>;
    MethodParameters:
             Name  Flags
      $anonymous0  

  K transform(java.util.Map$Entry<K, V>);
    descriptor: (Ljava/util/Map$Entry;)Ljava/lang/Object;
    flags: (0x0000) 
    Code:
      stack=1, locals=2, args_size=2
        start local 0 // com.google.common.collect.Maps$1 this
        start local 1 // java.util.Map$Entry entry
         0: .line 120
            aload 1 /* entry */
            invokeinterface java.util.Map$Entry.getKey:()Ljava/lang/Object;
            areturn
        end local 1 // java.util.Map$Entry entry
        end local 0 // com.google.common.collect.Maps$1 this
      LocalVariableTable:
        Start  End  Slot   Name  Signature
            0    1     0   this  Lcom/google/common/collect/Maps$1;
            0    1     1  entry  Ljava/util/Map$Entry<TK;TV;>;
    Signature: (Ljava/util/Map$Entry<TK;TV;>;)TK;
    MethodParameters:
       Name  Flags
      entry  

  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.Maps$1.transform:(Ljava/util/Map$Entry;)Ljava/lang/Object;
            areturn
      LocalVariableTable:
        Start  End  Slot  Name  Signature
}
Signature: Lcom/google/common/collect/TransformedIterator<Ljava/util/Map$Entry<TK;TV;>;TK;>;
SourceFile: "Maps.java"
EnclosingMethod: com.google.common.collect.Maps.keyIterator:(Ljava/util/Iterator;)Ljava/util/Iterator;
NestHost: com.google.common.collect.Maps
InnerClasses:
  com.google.common.collect.Maps$1
  public abstract Entry = java.util.Map$Entry of java.util.Map