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.AbstractMultiset$ElementSet extends com.google.common.collect.Multisets$ElementSet<E>
  minor version: 0
  major version: 59
  flags: flags: (0x0020) ACC_SUPER
  this_class: com.google.common.collect.AbstractMultiset$ElementSet
  super_class: com.google.common.collect.Multisets$ElementSet
{
  final com.google.common.collect.AbstractMultiset this$0;
    descriptor: Lcom/google/common/collect/AbstractMultiset;
    flags: (0x1010) ACC_FINAL, ACC_SYNTHETIC

  void <init>(com.google.common.collect.AbstractMultiset);
    descriptor: (Lcom/google/common/collect/AbstractMultiset;)V
    flags: (0x0000) 
    Code:
      stack=2, locals=2, args_size=2
        start local 0 // com.google.common.collect.AbstractMultiset$ElementSet this
         0: .line 147
            aload 0 /* this */
            aload 1
            putfield com.google.common.collect.AbstractMultiset$ElementSet.this$0:Lcom/google/common/collect/AbstractMultiset;
            aload 0 /* this */
            invokespecial com.google.common.collect.Multisets$ElementSet.<init>:()V
            return
        end local 0 // com.google.common.collect.AbstractMultiset$ElementSet this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/common/collect/AbstractMultiset$ElementSet;
    MethodParameters:
        Name  Flags
      this$0  final

  com.google.common.collect.Multiset<E> multiset();
    descriptor: ()Lcom/google/common/collect/Multiset;
    flags: (0x0000) 
    Code:
      stack=1, locals=1, args_size=1
        start local 0 // com.google.common.collect.AbstractMultiset$ElementSet this
         0: .line 150
            aload 0 /* this */
            getfield com.google.common.collect.AbstractMultiset$ElementSet.this$0:Lcom/google/common/collect/AbstractMultiset;
            areturn
        end local 0 // com.google.common.collect.AbstractMultiset$ElementSet this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/common/collect/AbstractMultiset$ElementSet;
    Signature: ()Lcom/google/common/collect/Multiset<TE;>;

  public java.util.Iterator<E> iterator();
    descriptor: ()Ljava/util/Iterator;
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=1, locals=1, args_size=1
        start local 0 // com.google.common.collect.AbstractMultiset$ElementSet this
         0: .line 155
            aload 0 /* this */
            getfield com.google.common.collect.AbstractMultiset$ElementSet.this$0:Lcom/google/common/collect/AbstractMultiset;
            invokevirtual com.google.common.collect.AbstractMultiset.elementIterator:()Ljava/util/Iterator;
            areturn
        end local 0 // com.google.common.collect.AbstractMultiset$ElementSet this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/common/collect/AbstractMultiset$ElementSet;
    Signature: ()Ljava/util/Iterator<TE;>;
}
Signature: Lcom/google/common/collect/Multisets$ElementSet<TE;>;
SourceFile: "AbstractMultiset.java"
NestHost: com.google.common.collect.AbstractMultiset
InnerClasses:
  ElementSet = com.google.common.collect.AbstractMultiset$ElementSet of com.google.common.collect.AbstractMultiset
  abstract ElementSet = com.google.common.collect.Multisets$ElementSet of com.google.common.collect.Multisets