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.MultimapBuilder$4 extends com.google.common.collect.MultimapBuilder$MultimapBuilderWithKeys<K0>
  minor version: 0
  major version: 59
  flags: flags: (0x0020) ACC_SUPER
  this_class: com.google.common.collect.MultimapBuilder$4
  super_class: com.google.common.collect.MultimapBuilder$MultimapBuilderWithKeys
{
  private final java.lang.Class val$keyClass;
    descriptor: Ljava/lang/Class;
    flags: (0x1012) ACC_PRIVATE, ACC_FINAL, ACC_SYNTHETIC

  void <init>(java.lang.Class);
    descriptor: (Ljava/lang/Class;)V
    flags: (0x0000) 
    Code:
      stack=2, locals=2, args_size=2
        start local 0 // com.google.common.collect.MultimapBuilder$4 this
         0: .line 174
            aload 0 /* this */
            aload 1
            putfield com.google.common.collect.MultimapBuilder$4.val$keyClass:Ljava/lang/Class;
            aload 0 /* this */
            invokespecial com.google.common.collect.MultimapBuilder$MultimapBuilderWithKeys.<init>:()V
            return
        end local 0 // com.google.common.collect.MultimapBuilder$4 this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/common/collect/MultimapBuilder$4;
    MethodParameters:
              Name  Flags
      val$keyClass  final

  <K extends K0, V> java.util.Map<K, java.util.Collection<V>> createMap();
    descriptor: ()Ljava/util/Map;
    flags: (0x0000) 
    Code:
      stack=3, locals=1, args_size=1
        start local 0 // com.google.common.collect.MultimapBuilder$4 this
         0: .line 180
            new java.util.EnumMap
            dup
            aload 0 /* this */
            getfield com.google.common.collect.MultimapBuilder$4.val$keyClass:Ljava/lang/Class;
            invokespecial java.util.EnumMap.<init>:(Ljava/lang/Class;)V
            areturn
        end local 0 // com.google.common.collect.MultimapBuilder$4 this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/common/collect/MultimapBuilder$4;
    Signature: <K:TK0;V:Ljava/lang/Object;>()Ljava/util/Map<TK;Ljava/util/Collection<TV;>;>;
}
Signature: Lcom/google/common/collect/MultimapBuilder$MultimapBuilderWithKeys<TK0;>;
SourceFile: "MultimapBuilder.java"
EnclosingMethod: com.google.common.collect.MultimapBuilder.enumKeys:(Ljava/lang/Class;)Lcom/google/common/collect/MultimapBuilder$MultimapBuilderWithKeys;
NestHost: com.google.common.collect.MultimapBuilder
InnerClasses:
  com.google.common.collect.MultimapBuilder$4
  public abstract MultimapBuilderWithKeys = com.google.common.collect.MultimapBuilder$MultimapBuilderWithKeys of com.google.common.collect.MultimapBuilder