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.base.CharMatcher$JavaLetter extends com.google.common.base.CharMatcher
  minor version: 0
  major version: 59
  flags: flags: (0x0030) ACC_FINAL, ACC_SUPER
  this_class: com.google.common.base.CharMatcher$JavaLetter
  super_class: com.google.common.base.CharMatcher
{
  static final com.google.common.base.CharMatcher$JavaLetter INSTANCE;
    descriptor: Lcom/google/common/base/CharMatcher$JavaLetter;
    flags: (0x0018) ACC_STATIC, ACC_FINAL

  static void <clinit>();
    descriptor: ()V
    flags: (0x0008) ACC_STATIC
    Code:
      stack=2, locals=0, args_size=0
         0: .line 1381
            new com.google.common.base.CharMatcher$JavaLetter
            dup
            invokespecial com.google.common.base.CharMatcher$JavaLetter.<init>:()V
            putstatic com.google.common.base.CharMatcher$JavaLetter.INSTANCE:Lcom/google/common/base/CharMatcher$JavaLetter;
            return
      LocalVariableTable:
        Start  End  Slot  Name  Signature

  private void <init>();
    descriptor: ()V
    flags: (0x0002) ACC_PRIVATE
    Code:
      stack=1, locals=1, args_size=1
        start local 0 // com.google.common.base.CharMatcher$JavaLetter this
         0: .line 1379
            aload 0 /* this */
            invokespecial com.google.common.base.CharMatcher.<init>:()V
            return
        end local 0 // com.google.common.base.CharMatcher$JavaLetter this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/common/base/CharMatcher$JavaLetter;

  public boolean matches(char);
    descriptor: (C)Z
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=1, locals=2, args_size=2
        start local 0 // com.google.common.base.CharMatcher$JavaLetter this
        start local 1 // char c
         0: .line 1385
            iload 1 /* c */
            invokestatic java.lang.Character.isLetter:(C)Z
            ireturn
        end local 1 // char c
        end local 0 // com.google.common.base.CharMatcher$JavaLetter this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/common/base/CharMatcher$JavaLetter;
            0    1     1     c  C
    MethodParameters:
      Name  Flags
      c     

  public java.lang.String toString();
    descriptor: ()Ljava/lang/String;
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=1, locals=1, args_size=1
        start local 0 // com.google.common.base.CharMatcher$JavaLetter this
         0: .line 1390
            ldc "CharMatcher.javaLetter()"
            areturn
        end local 0 // com.google.common.base.CharMatcher$JavaLetter this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/common/base/CharMatcher$JavaLetter;
}
SourceFile: "CharMatcher.java"
NestHost: com.google.common.base.CharMatcher
InnerClasses:
  private final JavaLetter = com.google.common.base.CharMatcher$JavaLetter of com.google.common.base.CharMatcher