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.io.Files$1 implements com.google.common.graph.SuccessorsFunction<java.io.File>
  minor version: 0
  major version: 59
  flags: flags: (0x0020) ACC_SUPER
  this_class: com.google.common.io.Files$1
  super_class: java.lang.Object
{
  void <init>();
    descriptor: ()V
    flags: (0x0000) 
    Code:
      stack=1, locals=1, args_size=1
        start local 0 // com.google.common.io.Files$1 this
         0: .line 855
            aload 0 /* this */
            invokespecial java.lang.Object.<init>:()V
            return
        end local 0 // com.google.common.io.Files$1 this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/common/io/Files$1;

  public java.lang.Iterable<java.io.File> successors(java.io.File);
    descriptor: (Ljava/io/File;)Ljava/lang/Iterable;
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=1, locals=3, args_size=2
        start local 0 // com.google.common.io.Files$1 this
        start local 1 // java.io.File file
         0: .line 859
            aload 1 /* file */
            invokevirtual java.io.File.isDirectory:()Z
            ifeq 4
         1: .line 860
            aload 1 /* file */
            invokevirtual java.io.File.listFiles:()[Ljava/io/File;
            astore 2 /* files */
        start local 2 // java.io.File[] files
         2: .line 861
            aload 2 /* files */
            ifnull 4
         3: .line 862
            aload 2 /* files */
            invokestatic java.util.Arrays.asList:([Ljava/lang/Object;)Ljava/util/List;
            invokestatic java.util.Collections.unmodifiableList:(Ljava/util/List;)Ljava/util/List;
            areturn
        end local 2 // java.io.File[] files
         4: .line 866
      StackMap locals:
      StackMap stack:
            invokestatic com.google.common.collect.ImmutableList.of:()Lcom/google/common/collect/ImmutableList;
            areturn
        end local 1 // java.io.File file
        end local 0 // com.google.common.io.Files$1 this
      LocalVariableTable:
        Start  End  Slot   Name  Signature
            0    5     0   this  Lcom/google/common/io/Files$1;
            0    5     1   file  Ljava/io/File;
            2    4     2  files  [Ljava/io/File;
    Signature: (Ljava/io/File;)Ljava/lang/Iterable<Ljava/io/File;>;
    MethodParameters:
      Name  Flags
      file  

  public java.lang.Iterable successors(java.lang.Object);
    descriptor: (Ljava/lang/Object;)Ljava/lang/Iterable;
    flags: (0x1041) ACC_PUBLIC, ACC_BRIDGE, ACC_SYNTHETIC
    Code:
      stack=2, locals=2, args_size=2
         0: .line 1
            aload 0
            aload 1
            checkcast java.io.File
            invokevirtual com.google.common.io.Files$1.successors:(Ljava/io/File;)Ljava/lang/Iterable;
            areturn
      LocalVariableTable:
        Start  End  Slot  Name  Signature
}
Signature: Ljava/lang/Object;Lcom/google/common/graph/SuccessorsFunction<Ljava/io/File;>;
SourceFile: "Files.java"
EnclosingMethod: com.google.common.io.Files
NestHost: com.google.common.io.Files
InnerClasses:
  com.google.common.io.Files$1