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.BaseEncoding$4 implements java.lang.Appendable
  minor version: 0
  major version: 59
  flags: flags: (0x0020) ACC_SUPER
  this_class: com.google.common.io.BaseEncoding$4
  super_class: java.lang.Object
{
  int charsUntilSeparator;
    descriptor: I
    flags: (0x0000) 

  private final java.lang.Appendable val$delegate;
    descriptor: Ljava/lang/Appendable;
    flags: (0x1012) ACC_PRIVATE, ACC_FINAL, ACC_SYNTHETIC

  private final java.lang.String val$separator;
    descriptor: Ljava/lang/String;
    flags: (0x1012) ACC_PRIVATE, ACC_FINAL, ACC_SYNTHETIC

  private final int val$afterEveryChars;
    descriptor: I
    flags: (0x1012) ACC_PRIVATE, ACC_FINAL, ACC_SYNTHETIC

  void <init>(int, java.lang.Appendable, java.lang.String);
    descriptor: (ILjava/lang/Appendable;Ljava/lang/String;)V
    flags: (0x0000) 
    Code:
      stack=2, locals=4, args_size=4
        start local 0 // com.google.common.io.BaseEncoding$4 this
         0: .line 1005
            aload 0 /* this */
            iload 1
            putfield com.google.common.io.BaseEncoding$4.val$afterEveryChars:I
            aload 0 /* this */
            aload 2
            putfield com.google.common.io.BaseEncoding$4.val$delegate:Ljava/lang/Appendable;
            aload 0 /* this */
            aload 3
            putfield com.google.common.io.BaseEncoding$4.val$separator:Ljava/lang/String;
            aload 0 /* this */
            invokespecial java.lang.Object.<init>:()V
         1: .line 1006
            aload 0 /* this */
            iload 1
            putfield com.google.common.io.BaseEncoding$4.charsUntilSeparator:I
         2: .line 1005
            return
        end local 0 // com.google.common.io.BaseEncoding$4 this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    3     0  this  Lcom/google/common/io/BaseEncoding$4;
    MethodParameters:
                     Name  Flags
      val$afterEveryChars  final
      val$delegate         final
      val$separator        final

  public java.lang.Appendable append(char);
    descriptor: (C)Ljava/lang/Appendable;
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=3, locals=2, args_size=2
        start local 0 // com.google.common.io.BaseEncoding$4 this
        start local 1 // char c
         0: .line 1010
            aload 0 /* this */
            getfield com.google.common.io.BaseEncoding$4.charsUntilSeparator:I
            ifne 3
         1: .line 1011
            aload 0 /* this */
            getfield com.google.common.io.BaseEncoding$4.val$delegate:Ljava/lang/Appendable;
            aload 0 /* this */
            getfield com.google.common.io.BaseEncoding$4.val$separator:Ljava/lang/String;
            invokeinterface java.lang.Appendable.append:(Ljava/lang/CharSequence;)Ljava/lang/Appendable;
            pop
         2: .line 1012
            aload 0 /* this */
            aload 0 /* this */
            getfield com.google.common.io.BaseEncoding$4.val$afterEveryChars:I
            putfield com.google.common.io.BaseEncoding$4.charsUntilSeparator:I
         3: .line 1014
      StackMap locals:
      StackMap stack:
            aload 0 /* this */
            getfield com.google.common.io.BaseEncoding$4.val$delegate:Ljava/lang/Appendable;
            iload 1 /* c */
            invokeinterface java.lang.Appendable.append:(C)Ljava/lang/Appendable;
            pop
         4: .line 1015
            aload 0 /* this */
            dup
            getfield com.google.common.io.BaseEncoding$4.charsUntilSeparator:I
            iconst_1
            isub
            putfield com.google.common.io.BaseEncoding$4.charsUntilSeparator:I
         5: .line 1016
            aload 0 /* this */
            areturn
        end local 1 // char c
        end local 0 // com.google.common.io.BaseEncoding$4 this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    6     0  this  Lcom/google/common/io/BaseEncoding$4;
            0    6     1     c  C
    Exceptions:
      throws java.io.IOException
    MethodParameters:
      Name  Flags
      c     

  public java.lang.Appendable append(java.lang.CharSequence, int, int);
    descriptor: (Ljava/lang/CharSequence;II)Ljava/lang/Appendable;
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=2, locals=4, args_size=4
        start local 0 // com.google.common.io.BaseEncoding$4 this
        start local 1 // java.lang.CharSequence chars
        start local 2 // int off
        start local 3 // int len
         0: .line 1021
            new java.lang.UnsupportedOperationException
            dup
            invokespecial java.lang.UnsupportedOperationException.<init>:()V
            athrow
        end local 3 // int len
        end local 2 // int off
        end local 1 // java.lang.CharSequence chars
        end local 0 // com.google.common.io.BaseEncoding$4 this
      LocalVariableTable:
        Start  End  Slot   Name  Signature
            0    1     0   this  Lcom/google/common/io/BaseEncoding$4;
            0    1     1  chars  Ljava/lang/CharSequence;
            0    1     2    off  I
            0    1     3    len  I
    Exceptions:
      throws java.io.IOException
    RuntimeVisibleTypeAnnotations: 
      METHOD_FORMAL_PARAMETER
        org.checkerframework.checker.nullness.qual.Nullable()
    MethodParameters:
       Name  Flags
      chars  
      off    
      len    

  public java.lang.Appendable append(java.lang.CharSequence);
    descriptor: (Ljava/lang/CharSequence;)Ljava/lang/Appendable;
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=2, locals=2, args_size=2
        start local 0 // com.google.common.io.BaseEncoding$4 this
        start local 1 // java.lang.CharSequence chars
         0: .line 1026
            new java.lang.UnsupportedOperationException
            dup
            invokespecial java.lang.UnsupportedOperationException.<init>:()V
            athrow
        end local 1 // java.lang.CharSequence chars
        end local 0 // com.google.common.io.BaseEncoding$4 this
      LocalVariableTable:
        Start  End  Slot   Name  Signature
            0    1     0   this  Lcom/google/common/io/BaseEncoding$4;
            0    1     1  chars  Ljava/lang/CharSequence;
    Exceptions:
      throws java.io.IOException
    RuntimeVisibleTypeAnnotations: 
      METHOD_FORMAL_PARAMETER
        org.checkerframework.checker.nullness.qual.Nullable()
    MethodParameters:
       Name  Flags
      chars  
}
SourceFile: "BaseEncoding.java"
EnclosingMethod: com.google.common.io.BaseEncoding.separatingAppendable:(Ljava/lang/Appendable;Ljava/lang/String;I)Ljava/lang/Appendable;
NestHost: com.google.common.io.BaseEncoding
InnerClasses:
  com.google.common.io.BaseEncoding$4