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.Sets$1 extends com.google.common.collect.Sets$SetView<E>
  minor version: 0
  major version: 59
  flags: flags: (0x0020) ACC_SUPER
  this_class: com.google.common.collect.Sets$1
  super_class: com.google.common.collect.Sets$SetView
{
  private final java.util.Set val$set1;
    descriptor: Ljava/util/Set;
    flags: (0x1012) ACC_PRIVATE, ACC_FINAL, ACC_SYNTHETIC

  private final java.util.Set val$set2;
    descriptor: Ljava/util/Set;
    flags: (0x1012) ACC_PRIVATE, ACC_FINAL, ACC_SYNTHETIC

  void <init>(java.util.Set, java.util.Set);
    descriptor: (Ljava/util/Set;Ljava/util/Set;)V
    flags: (0x0000) 
    Code:
      stack=2, locals=3, args_size=3
        start local 0 // com.google.common.collect.Sets$1 this
         0: .line 728
            aload 0 /* this */
            aload 1
            putfield com.google.common.collect.Sets$1.val$set1:Ljava/util/Set;
            aload 0 /* this */
            aload 2
            putfield com.google.common.collect.Sets$1.val$set2:Ljava/util/Set;
            aload 0 /* this */
            invokespecial com.google.common.collect.Sets$SetView.<init>:()V
            return
        end local 0 // com.google.common.collect.Sets$1 this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/common/collect/Sets$1;
    MethodParameters:
          Name  Flags
      val$set1  final
      val$set2  final

  public int size();
    descriptor: ()I
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=2, locals=4, args_size=1
        start local 0 // com.google.common.collect.Sets$1 this
         0: .line 731
            aload 0 /* this */
            getfield com.google.common.collect.Sets$1.val$set1:Ljava/util/Set;
            invokeinterface java.util.Set.size:()I
            istore 1 /* size */
        start local 1 // int size
         1: .line 732
            aload 0 /* this */
            getfield com.google.common.collect.Sets$1.val$set2:Ljava/util/Set;
            invokeinterface java.util.Set.iterator:()Ljava/util/Iterator;
            astore 3
            goto 5
      StackMap locals: com.google.common.collect.Sets$1 int top java.util.Iterator
      StackMap stack:
         2: aload 3
            invokeinterface java.util.Iterator.next:()Ljava/lang/Object;
            checkcast java.lang.Object
            astore 2 /* e */
        start local 2 // java.lang.Object e
         3: .line 733
            aload 0 /* this */
            getfield com.google.common.collect.Sets$1.val$set1:Ljava/util/Set;
            aload 2 /* e */
            invokeinterface java.util.Set.contains:(Ljava/lang/Object;)Z
            ifne 5
         4: .line 734
            iinc 1 /* size */ 1
        end local 2 // java.lang.Object e
         5: .line 732
      StackMap locals:
      StackMap stack:
            aload 3
            invokeinterface java.util.Iterator.hasNext:()Z
            ifne 2
         6: .line 737
            iload 1 /* size */
            ireturn
        end local 1 // int size
        end local 0 // com.google.common.collect.Sets$1 this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    7     0  this  Lcom/google/common/collect/Sets$1;
            1    7     1  size  I
            3    5     2     e  TE;

  public boolean isEmpty();
    descriptor: ()Z
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=1, locals=1, args_size=1
        start local 0 // com.google.common.collect.Sets$1 this
         0: .line 742
            aload 0 /* this */
            getfield com.google.common.collect.Sets$1.val$set1:Ljava/util/Set;
            invokeinterface java.util.Set.isEmpty:()Z
            ifeq 1
            aload 0 /* this */
            getfield com.google.common.collect.Sets$1.val$set2:Ljava/util/Set;
            invokeinterface java.util.Set.isEmpty:()Z
            ifeq 1
            iconst_1
            ireturn
      StackMap locals:
      StackMap stack:
         1: iconst_0
            ireturn
        end local 0 // com.google.common.collect.Sets$1 this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    2     0  this  Lcom/google/common/collect/Sets$1;

  public com.google.common.collect.UnmodifiableIterator<E> iterator();
    descriptor: ()Lcom/google/common/collect/UnmodifiableIterator;
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=5, locals=1, args_size=1
        start local 0 // com.google.common.collect.Sets$1 this
         0: .line 747
            new com.google.common.collect.Sets$1$1
            dup
            aload 0 /* this */
            aload 0 /* this */
            getfield com.google.common.collect.Sets$1.val$set1:Ljava/util/Set;
            aload 0 /* this */
            getfield com.google.common.collect.Sets$1.val$set2:Ljava/util/Set;
            invokespecial com.google.common.collect.Sets$1$1.<init>:(Lcom/google/common/collect/Sets$1;Ljava/util/Set;Ljava/util/Set;)V
            areturn
        end local 0 // com.google.common.collect.Sets$1 this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/common/collect/Sets$1;
    Signature: ()Lcom/google/common/collect/UnmodifiableIterator<TE;>;

  public java.util.stream.Stream<E> stream();
    descriptor: ()Ljava/util/stream/Stream;
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=3, locals=1, args_size=1
        start local 0 // com.google.common.collect.Sets$1 this
         0: .line 769
            aload 0 /* this */
            getfield com.google.common.collect.Sets$1.val$set1:Ljava/util/Set;
            invokeinterface java.util.Set.stream:()Ljava/util/stream/Stream;
            aload 0 /* this */
            getfield com.google.common.collect.Sets$1.val$set2:Ljava/util/Set;
            invokeinterface java.util.Set.stream:()Ljava/util/stream/Stream;
            aload 0 /* this */
            getfield com.google.common.collect.Sets$1.val$set1:Ljava/util/Set;
            invokedynamic test(Ljava/util/Set;)Ljava/util/function/Predicate;
              Bootstrap: invokestatic java.lang.invoke.LambdaMetafactory.metafactory:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite;
                Method arguments:
                  (Ljava/lang/Object;)Z
                  com/google/common/collect/Sets$1.lambda$0(Ljava/util/Set;Ljava/lang/Object;)Z (6)
                  (Ljava/lang/Object;)Z
            invokeinterface java.util.stream.Stream.filter:(Ljava/util/function/Predicate;)Ljava/util/stream/Stream;
            invokestatic java.util.stream.Stream.concat:(Ljava/util/stream/Stream;Ljava/util/stream/Stream;)Ljava/util/stream/Stream;
            areturn
        end local 0 // com.google.common.collect.Sets$1 this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/common/collect/Sets$1;
    Signature: ()Ljava/util/stream/Stream<TE;>;

  public java.util.stream.Stream<E> parallelStream();
    descriptor: ()Ljava/util/stream/Stream;
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=1, locals=1, args_size=1
        start local 0 // com.google.common.collect.Sets$1 this
         0: .line 774
            aload 0 /* this */
            invokevirtual com.google.common.collect.Sets$1.stream:()Ljava/util/stream/Stream;
            invokeinterface java.util.stream.Stream.parallel:()Ljava/util/stream/BaseStream;
            checkcast java.util.stream.Stream
            areturn
        end local 0 // com.google.common.collect.Sets$1 this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/common/collect/Sets$1;
    Signature: ()Ljava/util/stream/Stream<TE;>;

  public boolean contains(java.lang.Object);
    descriptor: (Ljava/lang/Object;)Z
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=2, locals=2, args_size=2
        start local 0 // com.google.common.collect.Sets$1 this
        start local 1 // java.lang.Object object
         0: .line 779
            aload 0 /* this */
            getfield com.google.common.collect.Sets$1.val$set1:Ljava/util/Set;
            aload 1 /* object */
            invokeinterface java.util.Set.contains:(Ljava/lang/Object;)Z
            ifne 1
            aload 0 /* this */
            getfield com.google.common.collect.Sets$1.val$set2:Ljava/util/Set;
            aload 1 /* object */
            invokeinterface java.util.Set.contains:(Ljava/lang/Object;)Z
            ifne 1
            iconst_0
            ireturn
      StackMap locals:
      StackMap stack:
         1: iconst_1
            ireturn
        end local 1 // java.lang.Object object
        end local 0 // com.google.common.collect.Sets$1 this
      LocalVariableTable:
        Start  End  Slot    Name  Signature
            0    2     0    this  Lcom/google/common/collect/Sets$1;
            0    2     1  object  Ljava/lang/Object;
    MethodParameters:
        Name  Flags
      object  

  public <S extends java.util.Set<E>> S copyInto();
    descriptor: (Ljava/util/Set;)Ljava/util/Set;
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=2, locals=2, args_size=2
        start local 0 // com.google.common.collect.Sets$1 this
        start local 1 // java.util.Set set
         0: .line 784
            aload 1 /* set */
            aload 0 /* this */
            getfield com.google.common.collect.Sets$1.val$set1:Ljava/util/Set;
            invokeinterface java.util.Set.addAll:(Ljava/util/Collection;)Z
            pop
         1: .line 785
            aload 1 /* set */
            aload 0 /* this */
            getfield com.google.common.collect.Sets$1.val$set2:Ljava/util/Set;
            invokeinterface java.util.Set.addAll:(Ljava/util/Collection;)Z
            pop
         2: .line 786
            aload 1 /* set */
            areturn
        end local 1 // java.util.Set set
        end local 0 // com.google.common.collect.Sets$1 this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    3     0  this  Lcom/google/common/collect/Sets$1;
            0    3     1   set  TS;
    Signature: <S::Ljava/util/Set<TE;>;>(TS;)TS;
    MethodParameters:
      Name  Flags
      set   

  public com.google.common.collect.ImmutableSet<E> immutableCopy();
    descriptor: ()Lcom/google/common/collect/ImmutableSet;
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=2, locals=1, args_size=1
        start local 0 // com.google.common.collect.Sets$1 this
         0: .line 791
            new com.google.common.collect.ImmutableSet$Builder
            dup
            invokespecial com.google.common.collect.ImmutableSet$Builder.<init>:()V
            aload 0 /* this */
            getfield com.google.common.collect.Sets$1.val$set1:Ljava/util/Set;
            invokevirtual com.google.common.collect.ImmutableSet$Builder.addAll:(Ljava/lang/Iterable;)Lcom/google/common/collect/ImmutableSet$Builder;
            aload 0 /* this */
            getfield com.google.common.collect.Sets$1.val$set2:Ljava/util/Set;
            invokevirtual com.google.common.collect.ImmutableSet$Builder.addAll:(Ljava/lang/Iterable;)Lcom/google/common/collect/ImmutableSet$Builder;
            invokevirtual com.google.common.collect.ImmutableSet$Builder.build:()Lcom/google/common/collect/ImmutableSet;
            areturn
        end local 0 // com.google.common.collect.Sets$1 this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/common/collect/Sets$1;
    Signature: ()Lcom/google/common/collect/ImmutableSet<TE;>;

  public java.util.Iterator iterator();
    descriptor: ()Ljava/util/Iterator;
    flags: (0x1041) ACC_PUBLIC, ACC_BRIDGE, ACC_SYNTHETIC
    Code:
      stack=1, locals=1, args_size=1
         0: .line 1
            aload 0
            invokevirtual com.google.common.collect.Sets$1.iterator:()Lcom/google/common/collect/UnmodifiableIterator;
            areturn
      LocalVariableTable:
        Start  End  Slot  Name  Signature

  private static boolean lambda$0(java.util.Set, java.lang.Object);
    descriptor: (Ljava/util/Set;Ljava/lang/Object;)Z
    flags: (0x100a) ACC_PRIVATE, ACC_STATIC, ACC_SYNTHETIC
    Code:
      stack=2, locals=2, args_size=2
        start local 1 // java.lang.Object e
         0: .line 769
            aload 0
            aload 1 /* e */
            invokeinterface java.util.Set.contains:(Ljava/lang/Object;)Z
            ifeq 1
            iconst_0
            goto 2
      StackMap locals:
      StackMap stack:
         1: iconst_1
      StackMap locals:
      StackMap stack: int
         2: ireturn
        end local 1 // java.lang.Object e
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    3     1     e  Ljava/lang/Object;
}
Signature: Lcom/google/common/collect/Sets$SetView<TE;>;
SourceFile: "Sets.java"
EnclosingMethod: com.google.common.collect.Sets.union:(Ljava/util/Set;Ljava/util/Set;)Lcom/google/common/collect/Sets$SetView;
NestHost: com.google.common.collect.Sets
InnerClasses:
  public Builder = com.google.common.collect.ImmutableSet$Builder of com.google.common.collect.ImmutableSet
  com.google.common.collect.Sets$1
  com.google.common.collect.Sets$1$1
  public abstract SetView = com.google.common.collect.Sets$SetView of com.google.common.collect.Sets
  public final Lookup = java.lang.invoke.MethodHandles$Lookup of java.lang.invoke.MethodHandles