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. 
final class com.google.common.collect.SingletonImmutableSet<E> extends com.google.common.collect.ImmutableSet<E>
  minor version: 0
  major version: 59
  flags: flags: (0x0030) ACC_FINAL, ACC_SUPER
  this_class: com.google.common.collect.SingletonImmutableSet
  super_class: com.google.common.collect.ImmutableSet
{
  final transient E element;
    descriptor: Ljava/lang/Object;
    flags: (0x0090) ACC_FINAL, ACC_TRANSIENT
    Signature: TE;

  private transient int cachedHashCode;
    descriptor: I
    flags: (0x0082) ACC_PRIVATE, ACC_TRANSIENT
    RuntimeVisibleAnnotations: 
      com.google.errorprone.annotations.concurrent.LazyInit()

  void <init>();
    descriptor: (Ljava/lang/Object;)V
    flags: (0x0000) 
    Code:
      stack=2, locals=2, args_size=2
        start local 0 // com.google.common.collect.SingletonImmutableSet this
        start local 1 // java.lang.Object element
         0: .line 43
            aload 0 /* this */
            invokespecial com.google.common.collect.ImmutableSet.<init>:()V
         1: .line 44
            aload 0 /* this */
            aload 1 /* element */
            invokestatic com.google.common.base.Preconditions.checkNotNull:(Ljava/lang/Object;)Ljava/lang/Object;
            putfield com.google.common.collect.SingletonImmutableSet.element:Ljava/lang/Object;
         2: .line 45
            return
        end local 1 // java.lang.Object element
        end local 0 // com.google.common.collect.SingletonImmutableSet this
      LocalVariableTable:
        Start  End  Slot     Name  Signature
            0    3     0     this  Lcom/google/common/collect/SingletonImmutableSet<TE;>;
            0    3     1  element  TE;
    Signature: (TE;)V
    MethodParameters:
         Name  Flags
      element  

  void <init>(E, );
    descriptor: (Ljava/lang/Object;I)V
    flags: (0x0000) 
    Code:
      stack=2, locals=3, args_size=3
        start local 0 // com.google.common.collect.SingletonImmutableSet this
        start local 1 // java.lang.Object element
        start local 2 // int hashCode
         0: .line 47
            aload 0 /* this */
            invokespecial com.google.common.collect.ImmutableSet.<init>:()V
         1: .line 49
            aload 0 /* this */
            aload 1 /* element */
            putfield com.google.common.collect.SingletonImmutableSet.element:Ljava/lang/Object;
         2: .line 50
            aload 0 /* this */
            iload 2 /* hashCode */
            putfield com.google.common.collect.SingletonImmutableSet.cachedHashCode:I
         3: .line 51
            return
        end local 2 // int hashCode
        end local 1 // java.lang.Object element
        end local 0 // com.google.common.collect.SingletonImmutableSet this
      LocalVariableTable:
        Start  End  Slot      Name  Signature
            0    4     0      this  Lcom/google/common/collect/SingletonImmutableSet<TE;>;
            0    4     1   element  TE;
            0    4     2  hashCode  I
    Signature: (TE;I)V
    MethodParameters:
          Name  Flags
      element   
      hashCode  

  public int size();
    descriptor: ()I
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=1, locals=1, args_size=1
        start local 0 // com.google.common.collect.SingletonImmutableSet this
         0: .line 55
            iconst_1
            ireturn
        end local 0 // com.google.common.collect.SingletonImmutableSet this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/common/collect/SingletonImmutableSet<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.SingletonImmutableSet this
        start local 1 // java.lang.Object target
         0: .line 60
            aload 0 /* this */
            getfield com.google.common.collect.SingletonImmutableSet.element:Ljava/lang/Object;
            aload 1 /* target */
            invokevirtual java.lang.Object.equals:(Ljava/lang/Object;)Z
            ireturn
        end local 1 // java.lang.Object target
        end local 0 // com.google.common.collect.SingletonImmutableSet this
      LocalVariableTable:
        Start  End  Slot    Name  Signature
            0    1     0    this  Lcom/google/common/collect/SingletonImmutableSet<TE;>;
            0    1     1  target  Ljava/lang/Object;
    MethodParameters:
        Name  Flags
      target  

  public com.google.common.collect.UnmodifiableIterator<E> iterator();
    descriptor: ()Lcom/google/common/collect/UnmodifiableIterator;
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=1, locals=1, args_size=1
        start local 0 // com.google.common.collect.SingletonImmutableSet this
         0: .line 65
            aload 0 /* this */
            getfield com.google.common.collect.SingletonImmutableSet.element:Ljava/lang/Object;
            invokestatic com.google.common.collect.Iterators.singletonIterator:(Ljava/lang/Object;)Lcom/google/common/collect/UnmodifiableIterator;
            areturn
        end local 0 // com.google.common.collect.SingletonImmutableSet this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/common/collect/SingletonImmutableSet<TE;>;
    Signature: ()Lcom/google/common/collect/UnmodifiableIterator<TE;>;

  com.google.common.collect.ImmutableList<E> createAsList();
    descriptor: ()Lcom/google/common/collect/ImmutableList;
    flags: (0x0000) 
    Code:
      stack=1, locals=1, args_size=1
        start local 0 // com.google.common.collect.SingletonImmutableSet this
         0: .line 70
            aload 0 /* this */
            getfield com.google.common.collect.SingletonImmutableSet.element:Ljava/lang/Object;
            invokestatic com.google.common.collect.ImmutableList.of:(Ljava/lang/Object;)Lcom/google/common/collect/ImmutableList;
            areturn
        end local 0 // com.google.common.collect.SingletonImmutableSet this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/common/collect/SingletonImmutableSet<TE;>;
    Signature: ()Lcom/google/common/collect/ImmutableList<TE;>;

  boolean isPartialView();
    descriptor: ()Z
    flags: (0x0000) 
    Code:
      stack=1, locals=1, args_size=1
        start local 0 // com.google.common.collect.SingletonImmutableSet this
         0: .line 75
            iconst_0
            ireturn
        end local 0 // com.google.common.collect.SingletonImmutableSet this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/common/collect/SingletonImmutableSet<TE;>;

  int copyIntoArray(java.lang.Object[], int);
    descriptor: ([Ljava/lang/Object;I)I
    flags: (0x0000) 
    Code:
      stack=3, locals=3, args_size=3
        start local 0 // com.google.common.collect.SingletonImmutableSet this
        start local 1 // java.lang.Object[] dst
        start local 2 // int offset
         0: .line 80
            aload 1 /* dst */
            iload 2 /* offset */
            aload 0 /* this */
            getfield com.google.common.collect.SingletonImmutableSet.element:Ljava/lang/Object;
            aastore
         1: .line 81
            iload 2 /* offset */
            iconst_1
            iadd
            ireturn
        end local 2 // int offset
        end local 1 // java.lang.Object[] dst
        end local 0 // com.google.common.collect.SingletonImmutableSet this
      LocalVariableTable:
        Start  End  Slot    Name  Signature
            0    2     0    this  Lcom/google/common/collect/SingletonImmutableSet<TE;>;
            0    2     1     dst  [Ljava/lang/Object;
            0    2     2  offset  I
    MethodParameters:
        Name  Flags
      dst     
      offset  

  public final int hashCode();
    descriptor: ()I
    flags: (0x0011) ACC_PUBLIC, ACC_FINAL
    Code:
      stack=3, locals=2, args_size=1
        start local 0 // com.google.common.collect.SingletonImmutableSet this
         0: .line 87
            aload 0 /* this */
            getfield com.google.common.collect.SingletonImmutableSet.cachedHashCode:I
            istore 1 /* code */
        start local 1 // int code
         1: .line 88
            iload 1 /* code */
            ifne 3
         2: .line 89
            aload 0 /* this */
            aload 0 /* this */
            getfield com.google.common.collect.SingletonImmutableSet.element:Ljava/lang/Object;
            invokevirtual java.lang.Object.hashCode:()I
            dup
            istore 1 /* code */
            putfield com.google.common.collect.SingletonImmutableSet.cachedHashCode:I
         3: .line 91
      StackMap locals: int
      StackMap stack:
            iload 1 /* code */
            ireturn
        end local 1 // int code
        end local 0 // com.google.common.collect.SingletonImmutableSet this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    4     0  this  Lcom/google/common/collect/SingletonImmutableSet<TE;>;
            1    4     1  code  I

  boolean isHashCodeFast();
    descriptor: ()Z
    flags: (0x0000) 
    Code:
      stack=1, locals=1, args_size=1
        start local 0 // com.google.common.collect.SingletonImmutableSet this
         0: .line 96
            aload 0 /* this */
            getfield com.google.common.collect.SingletonImmutableSet.cachedHashCode:I
            ifeq 1
            iconst_1
            ireturn
      StackMap locals:
      StackMap stack:
         1: iconst_0
            ireturn
        end local 0 // com.google.common.collect.SingletonImmutableSet this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    2     0  this  Lcom/google/common/collect/SingletonImmutableSet<TE;>;

  public java.lang.String toString();
    descriptor: ()Ljava/lang/String;
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=3, locals=1, args_size=1
        start local 0 // com.google.common.collect.SingletonImmutableSet this
         0: .line 101
            new java.lang.StringBuilder
            dup
            bipush 91
            invokestatic java.lang.String.valueOf:(C)Ljava/lang/String;
            invokespecial java.lang.StringBuilder.<init>:(Ljava/lang/String;)V
            aload 0 /* this */
            getfield com.google.common.collect.SingletonImmutableSet.element:Ljava/lang/Object;
            invokevirtual java.lang.Object.toString:()Ljava/lang/String;
            invokevirtual java.lang.StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
            bipush 93
            invokevirtual java.lang.StringBuilder.append:(C)Ljava/lang/StringBuilder;
            invokevirtual java.lang.StringBuilder.toString:()Ljava/lang/String;
            areturn
        end local 0 // com.google.common.collect.SingletonImmutableSet this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/common/collect/SingletonImmutableSet<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.SingletonImmutableSet.iterator:()Lcom/google/common/collect/UnmodifiableIterator;
            areturn
      LocalVariableTable:
        Start  End  Slot  Name  Signature
}
Signature: <E:Ljava/lang/Object;>Lcom/google/common/collect/ImmutableSet<TE;>;
SourceFile: "SingletonImmutableSet.java"
    RuntimeInvisibleAnnotations: 
      com.google.common.annotations.GwtCompatible(serializable = true, emulated = true)