http://netty.io/netty-all/: Netty is an asynchronous event-driven network application framework for rapid development of maintainable high performance protocol servers and clients. (The Netty Project) 
public final class io.netty.util.internal.ConcurrentSet<E> extends java.util.AbstractSet<E> implements java.io.Serializable
  minor version: 0
  major version: 59
  flags: flags: (0x0031) ACC_PUBLIC, ACC_FINAL, ACC_SUPER
  this_class: io.netty.util.internal.ConcurrentSet
  super_class: java.util.AbstractSet
{
  private static final long serialVersionUID;
    descriptor: J
    flags: (0x001a) ACC_PRIVATE, ACC_STATIC, ACC_FINAL
    ConstantValue: -6761513279741915432

  private final java.util.concurrent.ConcurrentMap<E, java.lang.Boolean> map;
    descriptor: Ljava/util/concurrent/ConcurrentMap;
    flags: (0x0012) ACC_PRIVATE, ACC_FINAL
    Signature: Ljava/util/concurrent/ConcurrentMap<TE;Ljava/lang/Boolean;>;

  public void <init>();
    descriptor: ()V
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=2, locals=1, args_size=1
        start local 0 // io.netty.util.internal.ConcurrentSet this
         0: .line 32
            aload 0 /* this */
            invokespecial java.util.AbstractSet.<init>:()V
         1: .line 33
            aload 0 /* this */
            invokestatic io.netty.util.internal.PlatformDependent.newConcurrentHashMap:()Ljava/util/concurrent/ConcurrentMap;
            putfield io.netty.util.internal.ConcurrentSet.map:Ljava/util/concurrent/ConcurrentMap;
         2: .line 34
            return
        end local 0 // io.netty.util.internal.ConcurrentSet this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    3     0  this  Lio/netty/util/internal/ConcurrentSet<TE;>;

  public int size();
    descriptor: ()I
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=1, locals=1, args_size=1
        start local 0 // io.netty.util.internal.ConcurrentSet this
         0: .line 38
            aload 0 /* this */
            getfield io.netty.util.internal.ConcurrentSet.map:Ljava/util/concurrent/ConcurrentMap;
            invokeinterface java.util.concurrent.ConcurrentMap.size:()I
            ireturn
        end local 0 // io.netty.util.internal.ConcurrentSet this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lio/netty/util/internal/ConcurrentSet<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 // io.netty.util.internal.ConcurrentSet this
        start local 1 // java.lang.Object o
         0: .line 43
            aload 0 /* this */
            getfield io.netty.util.internal.ConcurrentSet.map:Ljava/util/concurrent/ConcurrentMap;
            aload 1 /* o */
            invokeinterface java.util.concurrent.ConcurrentMap.containsKey:(Ljava/lang/Object;)Z
            ireturn
        end local 1 // java.lang.Object o
        end local 0 // io.netty.util.internal.ConcurrentSet this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lio/netty/util/internal/ConcurrentSet<TE;>;
            0    1     1     o  Ljava/lang/Object;
    MethodParameters:
      Name  Flags
      o     

  public boolean add();
    descriptor: (Ljava/lang/Object;)Z
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=3, locals=2, args_size=2
        start local 0 // io.netty.util.internal.ConcurrentSet this
        start local 1 // java.lang.Object o
         0: .line 48
            aload 0 /* this */
            getfield io.netty.util.internal.ConcurrentSet.map:Ljava/util/concurrent/ConcurrentMap;
            aload 1 /* o */
            getstatic java.lang.Boolean.TRUE:Ljava/lang/Boolean;
            invokeinterface java.util.concurrent.ConcurrentMap.putIfAbsent:(Ljava/lang/Object;Ljava/lang/Object;)Ljava/lang/Object;
            ifnonnull 1
            iconst_1
            ireturn
      StackMap locals:
      StackMap stack:
         1: iconst_0
            ireturn
        end local 1 // java.lang.Object o
        end local 0 // io.netty.util.internal.ConcurrentSet this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    2     0  this  Lio/netty/util/internal/ConcurrentSet<TE;>;
            0    2     1     o  TE;
    Signature: (TE;)Z
    MethodParameters:
      Name  Flags
      o     

  public boolean remove(java.lang.Object);
    descriptor: (Ljava/lang/Object;)Z
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=2, locals=2, args_size=2
        start local 0 // io.netty.util.internal.ConcurrentSet this
        start local 1 // java.lang.Object o
         0: .line 53
            aload 0 /* this */
            getfield io.netty.util.internal.ConcurrentSet.map:Ljava/util/concurrent/ConcurrentMap;
            aload 1 /* o */
            invokeinterface java.util.concurrent.ConcurrentMap.remove:(Ljava/lang/Object;)Ljava/lang/Object;
            ifnull 1
            iconst_1
            ireturn
      StackMap locals:
      StackMap stack:
         1: iconst_0
            ireturn
        end local 1 // java.lang.Object o
        end local 0 // io.netty.util.internal.ConcurrentSet this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    2     0  this  Lio/netty/util/internal/ConcurrentSet<TE;>;
            0    2     1     o  Ljava/lang/Object;
    MethodParameters:
      Name  Flags
      o     

  public void clear();
    descriptor: ()V
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=1, locals=1, args_size=1
        start local 0 // io.netty.util.internal.ConcurrentSet this
         0: .line 58
            aload 0 /* this */
            getfield io.netty.util.internal.ConcurrentSet.map:Ljava/util/concurrent/ConcurrentMap;
            invokeinterface java.util.concurrent.ConcurrentMap.clear:()V
         1: .line 59
            return
        end local 0 // io.netty.util.internal.ConcurrentSet this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    2     0  this  Lio/netty/util/internal/ConcurrentSet<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 // io.netty.util.internal.ConcurrentSet this
         0: .line 63
            aload 0 /* this */
            getfield io.netty.util.internal.ConcurrentSet.map:Ljava/util/concurrent/ConcurrentMap;
            invokeinterface java.util.concurrent.ConcurrentMap.keySet:()Ljava/util/Set;
            invokeinterface java.util.Set.iterator:()Ljava/util/Iterator;
            areturn
        end local 0 // io.netty.util.internal.ConcurrentSet this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lio/netty/util/internal/ConcurrentSet<TE;>;
    Signature: ()Ljava/util/Iterator<TE;>;
}
Signature: <E:Ljava/lang/Object;>Ljava/util/AbstractSet<TE;>;Ljava/io/Serializable;
SourceFile: "ConcurrentSet.java"