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.CollectSpliterators$1FlatMapSpliterator implements java.util.Spliterator<T>
  minor version: 0
  major version: 59
  flags: flags: (0x0020) ACC_SUPER
  this_class: com.google.common.collect.CollectSpliterators$1FlatMapSpliterator
  super_class: java.lang.Object
{
  java.util.Spliterator<T> prefix;
    descriptor: Ljava/util/Spliterator;
    flags: (0x0000) 
    Signature: Ljava/util/Spliterator<TT;>;
    RuntimeVisibleTypeAnnotations: 
      FIELD
        org.checkerframework.checker.nullness.qual.Nullable()

  final java.util.Spliterator<F> from;
    descriptor: Ljava/util/Spliterator;
    flags: (0x0010) ACC_FINAL
    Signature: Ljava/util/Spliterator<TF;>;

  int characteristics;
    descriptor: I
    flags: (0x0000) 

  long estimatedSize;
    descriptor: J
    flags: (0x0000) 

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

  void <init>(java.util.Spliterator<T>, java.util.Spliterator<F>, int, );
    descriptor: (Ljava/util/Spliterator;Ljava/util/Spliterator;IJLjava/util/function/Function;)V
    flags: (0x0000) 
    Code:
      stack=3, locals=7, args_size=6
        start local 0 // com.google.common.collect.CollectSpliterators$1FlatMapSpliterator this
        start local 1 // java.util.Spliterator prefix
        start local 2 // java.util.Spliterator from
        start local 3 // int characteristics
        start local 4 // long estimatedSize
         0: .line 217
            aload 0 /* this */
            aload 6
            putfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.val$function:Ljava/util/function/Function;
         1: .line 216
            aload 0 /* this */
            invokespecial java.lang.Object.<init>:()V
         2: .line 218
            aload 0 /* this */
            aload 1 /* prefix */
            putfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.prefix:Ljava/util/Spliterator;
         3: .line 219
            aload 0 /* this */
            aload 2 /* from */
            putfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.from:Ljava/util/Spliterator;
         4: .line 220
            aload 0 /* this */
            iload 3 /* characteristics */
            putfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.characteristics:I
         5: .line 221
            aload 0 /* this */
            lload 4 /* estimatedSize */
            putfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.estimatedSize:J
         6: .line 222
            return
        end local 4 // long estimatedSize
        end local 3 // int characteristics
        end local 2 // java.util.Spliterator from
        end local 1 // java.util.Spliterator prefix
        end local 0 // com.google.common.collect.CollectSpliterators$1FlatMapSpliterator this
      LocalVariableTable:
        Start  End  Slot             Name  Signature
            0    7     0             this  Lcom/google/common/collect/CollectSpliterators$1FlatMapSpliterator;
            0    7     1           prefix  Ljava/util/Spliterator<TT;>;
            0    7     2             from  Ljava/util/Spliterator<TF;>;
            0    7     3  characteristics  I
            0    7     4    estimatedSize  J
    Signature: (Ljava/util/Spliterator<TT;>;Ljava/util/Spliterator<TF;>;IJ)V
    MethodParameters:
                 Name  Flags
      prefix           
      from             
      characteristics  
      estimatedSize    
      val$function     final

  public boolean tryAdvance(java.util.function.Consumer<? super T>);
    descriptor: (Ljava/util/function/Consumer;)Z
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=5, locals=2, args_size=2
        start local 0 // com.google.common.collect.CollectSpliterators$1FlatMapSpliterator this
        start local 1 // java.util.function.Consumer action
         0: .line 227
      StackMap locals:
      StackMap stack:
            aload 0 /* this */
            getfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.prefix:Ljava/util/Spliterator;
            ifnull 4
            aload 0 /* this */
            getfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.prefix:Ljava/util/Spliterator;
            aload 1 /* action */
            invokeinterface java.util.Spliterator.tryAdvance:(Ljava/util/function/Consumer;)Z
            ifeq 4
         1: .line 228
            aload 0 /* this */
            getfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.estimatedSize:J
            ldc 9223372036854775807
            lcmp
            ifeq 3
         2: .line 229
            aload 0 /* this */
            dup
            getfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.estimatedSize:J
            lconst_1
            lsub
            putfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.estimatedSize:J
         3: .line 231
      StackMap locals:
      StackMap stack:
            iconst_1
            ireturn
         4: .line 233
      StackMap locals:
      StackMap stack:
            aload 0 /* this */
            aconst_null
            putfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.prefix:Ljava/util/Spliterator;
         5: .line 235
            aload 0 /* this */
            getfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.from:Ljava/util/Spliterator;
            aload 0 /* this */
            aload 0 /* this */
            getfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.val$function:Ljava/util/function/Function;
            invokedynamic accept(Lcom/google/common/collect/CollectSpliterators$1FlatMapSpliterator;Ljava/util/function/Function;)Ljava/util/function/Consumer;
              Bootstrap: invokestatic java.lang.invoke.LambdaMetafactory.metafactory:(Ljava/lang/invoke/MethodHandles$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;)V
                  com/google/common/collect/CollectSpliterators$1FlatMapSpliterator.lambda$0(Ljava/util/function/Function;Ljava/lang/Object;)V (7)
                  (Ljava/lang/Object;)V
            invokeinterface java.util.Spliterator.tryAdvance:(Ljava/util/function/Consumer;)Z
            ifne 0
         6: .line 236
            iconst_0
            ireturn
        end local 1 // java.util.function.Consumer action
        end local 0 // com.google.common.collect.CollectSpliterators$1FlatMapSpliterator this
      LocalVariableTable:
        Start  End  Slot    Name  Signature
            0    7     0    this  Lcom/google/common/collect/CollectSpliterators$1FlatMapSpliterator;
            0    7     1  action  Ljava/util/function/Consumer<-TT;>;
    Signature: (Ljava/util/function/Consumer<-TT;>;)Z
    MethodParameters:
        Name  Flags
      action  

  public void forEachRemaining(java.util.function.Consumer<? super T>);
    descriptor: (Ljava/util/function/Consumer;)V
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=3, locals=2, args_size=2
        start local 0 // com.google.common.collect.CollectSpliterators$1FlatMapSpliterator this
        start local 1 // java.util.function.Consumer action
         0: .line 243
            aload 0 /* this */
            getfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.prefix:Ljava/util/Spliterator;
            ifnull 3
         1: .line 244
            aload 0 /* this */
            getfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.prefix:Ljava/util/Spliterator;
            aload 1 /* action */
            invokeinterface java.util.Spliterator.forEachRemaining:(Ljava/util/function/Consumer;)V
         2: .line 245
            aload 0 /* this */
            aconst_null
            putfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.prefix:Ljava/util/Spliterator;
         3: .line 247
      StackMap locals:
      StackMap stack:
            aload 0 /* this */
            getfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.from:Ljava/util/Spliterator;
            aload 0 /* this */
            getfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.val$function:Ljava/util/function/Function;
            aload 1 /* action */
            invokedynamic accept(Ljava/util/function/Function;Ljava/util/function/Consumer;)Ljava/util/function/Consumer;
              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;)V
                  com/google/common/collect/CollectSpliterators$1FlatMapSpliterator.lambda$1(Ljava/util/function/Function;Ljava/util/function/Consumer;Ljava/lang/Object;)V (6)
                  (Ljava/lang/Object;)V
            invokeinterface java.util.Spliterator.forEachRemaining:(Ljava/util/function/Consumer;)V
         4: .line 248
            aload 0 /* this */
            lconst_0
            putfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.estimatedSize:J
         5: .line 249
            return
        end local 1 // java.util.function.Consumer action
        end local 0 // com.google.common.collect.CollectSpliterators$1FlatMapSpliterator this
      LocalVariableTable:
        Start  End  Slot    Name  Signature
            0    6     0    this  Lcom/google/common/collect/CollectSpliterators$1FlatMapSpliterator;
            0    6     1  action  Ljava/util/function/Consumer<-TT;>;
    Signature: (Ljava/util/function/Consumer<-TT;>;)V
    MethodParameters:
        Name  Flags
      action  

  public java.util.Spliterator<T> trySplit();
    descriptor: ()Ljava/util/Spliterator;
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=8, locals=6, args_size=1
        start local 0 // com.google.common.collect.CollectSpliterators$1FlatMapSpliterator this
         0: .line 253
            aload 0 /* this */
            getfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.from:Ljava/util/Spliterator;
            invokeinterface java.util.Spliterator.trySplit:()Ljava/util/Spliterator;
            astore 1 /* fromSplit */
        start local 1 // java.util.Spliterator fromSplit
         1: .line 254
            aload 1 /* fromSplit */
            ifnull 12
         2: .line 255
            aload 0 /* this */
            getfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.characteristics:I
            bipush -65
            iand
            istore 2 /* splitCharacteristics */
        start local 2 // int splitCharacteristics
         3: .line 256
            aload 0 /* this */
            invokevirtual com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.estimateSize:()J
            lstore 3 /* estSplitSize */
        start local 3 // long estSplitSize
         4: .line 257
            lload 3 /* estSplitSize */
            ldc 9223372036854775807
            lcmp
            ifge 8
         5: .line 258
            lload 3 /* estSplitSize */
            ldc 2
            ldiv
            lstore 3 /* estSplitSize */
         6: .line 259
            aload 0 /* this */
            dup
            getfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.estimatedSize:J
            lload 3 /* estSplitSize */
            lsub
            putfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.estimatedSize:J
         7: .line 260
            aload 0 /* this */
            iload 2 /* splitCharacteristics */
            putfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.characteristics:I
         8: .line 263
      StackMap locals: java.util.Spliterator int long
      StackMap stack:
            new com.google.common.collect.CollectSpliterators$1FlatMapSpliterator
            dup
            aload 0 /* this */
            getfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.prefix:Ljava/util/Spliterator;
            aload 1 /* fromSplit */
            iload 2 /* splitCharacteristics */
            lload 3 /* estSplitSize */
            aload 0 /* this */
            getfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.val$function:Ljava/util/function/Function;
            invokespecial com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.<init>:(Ljava/util/Spliterator;Ljava/util/Spliterator;IJLjava/util/function/Function;)V
         9: .line 262
            astore 5 /* result */
        start local 5 // java.util.Spliterator result
        10: .line 264
            aload 0 /* this */
            aconst_null
            putfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.prefix:Ljava/util/Spliterator;
        11: .line 265
            aload 5 /* result */
            areturn
        end local 5 // java.util.Spliterator result
        end local 3 // long estSplitSize
        end local 2 // int splitCharacteristics
        12: .line 266
      StackMap locals:
      StackMap stack:
            aload 0 /* this */
            getfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.prefix:Ljava/util/Spliterator;
            ifnull 16
        13: .line 267
            aload 0 /* this */
            getfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.prefix:Ljava/util/Spliterator;
            astore 2 /* result */
        start local 2 // java.util.Spliterator result
        14: .line 268
            aload 0 /* this */
            aconst_null
            putfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.prefix:Ljava/util/Spliterator;
        15: .line 269
            aload 2 /* result */
            areturn
        end local 2 // java.util.Spliterator result
        16: .line 271
      StackMap locals:
      StackMap stack:
            aconst_null
            areturn
        end local 1 // java.util.Spliterator fromSplit
        end local 0 // com.google.common.collect.CollectSpliterators$1FlatMapSpliterator this
      LocalVariableTable:
        Start  End  Slot                  Name  Signature
            0   17     0                  this  Lcom/google/common/collect/CollectSpliterators$1FlatMapSpliterator;
            1   17     1             fromSplit  Ljava/util/Spliterator<TF;>;
            3   12     2  splitCharacteristics  I
            4   12     3          estSplitSize  J
           10   12     5                result  Ljava/util/Spliterator<TT;>;
           14   16     2                result  Ljava/util/Spliterator<TT;>;
    Signature: ()Ljava/util/Spliterator<TT;>;

  public long estimateSize();
    descriptor: ()J
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=5, locals=1, args_size=1
        start local 0 // com.google.common.collect.CollectSpliterators$1FlatMapSpliterator this
         0: .line 277
            aload 0 /* this */
            getfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.prefix:Ljava/util/Spliterator;
            ifnull 2
         1: .line 278
            aload 0 /* this */
            aload 0 /* this */
            getfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.estimatedSize:J
            aload 0 /* this */
            getfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.prefix:Ljava/util/Spliterator;
            invokeinterface java.util.Spliterator.estimateSize:()J
            invokestatic java.lang.Math.max:(JJ)J
            putfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.estimatedSize:J
         2: .line 280
      StackMap locals:
      StackMap stack:
            aload 0 /* this */
            getfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.estimatedSize:J
            lconst_0
            invokestatic java.lang.Math.max:(JJ)J
            lreturn
        end local 0 // com.google.common.collect.CollectSpliterators$1FlatMapSpliterator this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    3     0  this  Lcom/google/common/collect/CollectSpliterators$1FlatMapSpliterator;

  public int characteristics();
    descriptor: ()I
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=1, locals=1, args_size=1
        start local 0 // com.google.common.collect.CollectSpliterators$1FlatMapSpliterator this
         0: .line 285
            aload 0 /* this */
            getfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.characteristics:I
            ireturn
        end local 0 // com.google.common.collect.CollectSpliterators$1FlatMapSpliterator this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/common/collect/CollectSpliterators$1FlatMapSpliterator;

  private void lambda$0(java.util.function.Function, java.lang.Object);
    descriptor: (Ljava/util/function/Function;Ljava/lang/Object;)V
    flags: (0x1002) ACC_PRIVATE, ACC_SYNTHETIC
    Code:
      stack=3, locals=3, args_size=3
        start local 0 // com.google.common.collect.CollectSpliterators$1FlatMapSpliterator this
        start local 2 // java.lang.Object fromElement
         0: .line 235
            aload 0 /* this */
            aload 1
            aload 2 /* fromElement */
            invokeinterface java.util.function.Function.apply:(Ljava/lang/Object;)Ljava/lang/Object;
            checkcast java.util.Spliterator
            dup_x1
            putfield com.google.common.collect.CollectSpliterators$1FlatMapSpliterator.prefix:Ljava/util/Spliterator;
            return
        end local 2 // java.lang.Object fromElement
        end local 0 // com.google.common.collect.CollectSpliterators$1FlatMapSpliterator this
      LocalVariableTable:
        Start  End  Slot         Name  Signature
            0    1     0         this  Lcom/google/common/collect/CollectSpliterators$1FlatMapSpliterator;
            0    1     2  fromElement  TF;

  private static void lambda$1(java.util.function.Function, java.util.function.Consumer, java.lang.Object);
    descriptor: (Ljava/util/function/Function;Ljava/util/function/Consumer;Ljava/lang/Object;)V
    flags: (0x100a) ACC_PRIVATE, ACC_STATIC, ACC_SYNTHETIC
    Code:
      stack=2, locals=3, args_size=3
        start local 2 // java.lang.Object fromElement
         0: .line 247
            aload 0
            aload 2 /* fromElement */
            invokeinterface java.util.function.Function.apply:(Ljava/lang/Object;)Ljava/lang/Object;
            checkcast java.util.Spliterator
            aload 1
            invokeinterface java.util.Spliterator.forEachRemaining:(Ljava/util/function/Consumer;)V
            return
        end local 2 // java.lang.Object fromElement
      LocalVariableTable:
        Start  End  Slot         Name  Signature
            0    1     2  fromElement  TF;
}
Signature: Ljava/lang/Object;Ljava/util/Spliterator<TT;>;
SourceFile: "CollectSpliterators.java"
EnclosingMethod: com.google.common.collect.CollectSpliterators.flatMap:(Ljava/util/Spliterator;Ljava/util/function/Function;IJ)Ljava/util/Spliterator;
NestHost: com.google.common.collect.CollectSpliterators
InnerClasses:
  FlatMapSpliterator = com.google.common.collect.CollectSpliterators$1FlatMapSpliterator
  public final Lookup = java.lang.invoke.MethodHandles$Lookup of java.lang.invoke.MethodHandles