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.Converter$FunctionBasedConverter<A, B> extends com.google.common.base.Converter<A, B> implements java.io.Serializable
  minor version: 0
  major version: 59
  flags: flags: (0x0030) ACC_FINAL, ACC_SUPER
  this_class: com.google.common.base.Converter$FunctionBasedConverter
  super_class: com.google.common.base.Converter
{
  private final com.google.common.base.Function<? super A, ? extends B> forwardFunction;
    descriptor: Lcom/google/common/base/Function;
    flags: (0x0012) ACC_PRIVATE, ACC_FINAL
    Signature: Lcom/google/common/base/Function<-TA;+TB;>;

  private final com.google.common.base.Function<? super B, ? extends A> backwardFunction;
    descriptor: Lcom/google/common/base/Function;
    flags: (0x0012) ACC_PRIVATE, ACC_FINAL
    Signature: Lcom/google/common/base/Function<-TB;+TA;>;

  private void <init>(com.google.common.base.Function<? super A, ? extends B>, com.google.common.base.Function<? super B, ? extends A>);
    descriptor: (Lcom/google/common/base/Function;Lcom/google/common/base/Function;)V
    flags: (0x0002) ACC_PRIVATE
    Code:
      stack=2, locals=3, args_size=3
        start local 0 // com.google.common.base.Converter$FunctionBasedConverter this
        start local 1 // com.google.common.base.Function forwardFunction
        start local 2 // com.google.common.base.Function backwardFunction
         0: .line 436
            aload 0 /* this */
            invokespecial com.google.common.base.Converter.<init>:()V
         1: .line 439
            aload 0 /* this */
            aload 1 /* forwardFunction */
            invokestatic com.google.common.base.Preconditions.checkNotNull:(Ljava/lang/Object;)Ljava/lang/Object;
            checkcast com.google.common.base.Function
            putfield com.google.common.base.Converter$FunctionBasedConverter.forwardFunction:Lcom/google/common/base/Function;
         2: .line 440
            aload 0 /* this */
            aload 2 /* backwardFunction */
            invokestatic com.google.common.base.Preconditions.checkNotNull:(Ljava/lang/Object;)Ljava/lang/Object;
            checkcast com.google.common.base.Function
            putfield com.google.common.base.Converter$FunctionBasedConverter.backwardFunction:Lcom/google/common/base/Function;
         3: .line 441
            return
        end local 2 // com.google.common.base.Function backwardFunction
        end local 1 // com.google.common.base.Function forwardFunction
        end local 0 // com.google.common.base.Converter$FunctionBasedConverter this
      LocalVariableTable:
        Start  End  Slot              Name  Signature
            0    4     0              this  Lcom/google/common/base/Converter$FunctionBasedConverter<TA;TB;>;
            0    4     1   forwardFunction  Lcom/google/common/base/Function<-TA;+TB;>;
            0    4     2  backwardFunction  Lcom/google/common/base/Function<-TB;+TA;>;
    Signature: (Lcom/google/common/base/Function<-TA;+TB;>;Lcom/google/common/base/Function<-TB;+TA;>;)V
    MethodParameters:
                  Name  Flags
      forwardFunction   
      backwardFunction  

  protected B doForward();
    descriptor: (Ljava/lang/Object;)Ljava/lang/Object;
    flags: (0x0004) ACC_PROTECTED
    Code:
      stack=2, locals=2, args_size=2
        start local 0 // com.google.common.base.Converter$FunctionBasedConverter this
        start local 1 // java.lang.Object a
         0: .line 445
            aload 0 /* this */
            getfield com.google.common.base.Converter$FunctionBasedConverter.forwardFunction:Lcom/google/common/base/Function;
            aload 1 /* a */
            invokeinterface com.google.common.base.Function.apply:(Ljava/lang/Object;)Ljava/lang/Object;
            areturn
        end local 1 // java.lang.Object a
        end local 0 // com.google.common.base.Converter$FunctionBasedConverter this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/common/base/Converter$FunctionBasedConverter<TA;TB;>;
            0    1     1     a  TA;
    Signature: (TA;)TB;
    MethodParameters:
      Name  Flags
      a     

  protected A doBackward();
    descriptor: (Ljava/lang/Object;)Ljava/lang/Object;
    flags: (0x0004) ACC_PROTECTED
    Code:
      stack=2, locals=2, args_size=2
        start local 0 // com.google.common.base.Converter$FunctionBasedConverter this
        start local 1 // java.lang.Object b
         0: .line 450
            aload 0 /* this */
            getfield com.google.common.base.Converter$FunctionBasedConverter.backwardFunction:Lcom/google/common/base/Function;
            aload 1 /* b */
            invokeinterface com.google.common.base.Function.apply:(Ljava/lang/Object;)Ljava/lang/Object;
            areturn
        end local 1 // java.lang.Object b
        end local 0 // com.google.common.base.Converter$FunctionBasedConverter this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/common/base/Converter$FunctionBasedConverter<TA;TB;>;
            0    1     1     b  TB;
    Signature: (TB;)TA;
    MethodParameters:
      Name  Flags
      b     

  public boolean equals(java.lang.Object);
    descriptor: (Ljava/lang/Object;)Z
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=2, locals=3, args_size=2
        start local 0 // com.google.common.base.Converter$FunctionBasedConverter this
        start local 1 // java.lang.Object object
         0: .line 455
            aload 1 /* object */
            instanceof com.google.common.base.Converter$FunctionBasedConverter
            ifeq 6
         1: .line 456
            aload 1 /* object */
            checkcast com.google.common.base.Converter$FunctionBasedConverter
            astore 2 /* that */
        start local 2 // com.google.common.base.Converter$FunctionBasedConverter that
         2: .line 457
            aload 0 /* this */
            getfield com.google.common.base.Converter$FunctionBasedConverter.forwardFunction:Lcom/google/common/base/Function;
            aload 2 /* that */
            getfield com.google.common.base.Converter$FunctionBasedConverter.forwardFunction:Lcom/google/common/base/Function;
            invokeinterface com.google.common.base.Function.equals:(Ljava/lang/Object;)Z
            ifeq 5
         3: .line 458
            aload 0 /* this */
            getfield com.google.common.base.Converter$FunctionBasedConverter.backwardFunction:Lcom/google/common/base/Function;
            aload 2 /* that */
            getfield com.google.common.base.Converter$FunctionBasedConverter.backwardFunction:Lcom/google/common/base/Function;
            invokeinterface com.google.common.base.Function.equals:(Ljava/lang/Object;)Z
            ifeq 5
         4: .line 457
            iconst_1
            ireturn
      StackMap locals: com.google.common.base.Converter$FunctionBasedConverter
      StackMap stack:
         5: iconst_0
            ireturn
        end local 2 // com.google.common.base.Converter$FunctionBasedConverter that
         6: .line 460
      StackMap locals:
      StackMap stack:
            iconst_0
            ireturn
        end local 1 // java.lang.Object object
        end local 0 // com.google.common.base.Converter$FunctionBasedConverter this
      LocalVariableTable:
        Start  End  Slot    Name  Signature
            0    7     0    this  Lcom/google/common/base/Converter$FunctionBasedConverter<TA;TB;>;
            0    7     1  object  Ljava/lang/Object;
            2    6     2    that  Lcom/google/common/base/Converter$FunctionBasedConverter<**>;
    RuntimeVisibleTypeAnnotations: 
      METHOD_FORMAL_PARAMETER
        org.checkerframework.checker.nullness.qual.Nullable()
    MethodParameters:
        Name  Flags
      object  

  public int hashCode();
    descriptor: ()I
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=2, locals=1, args_size=1
        start local 0 // com.google.common.base.Converter$FunctionBasedConverter this
         0: .line 465
            aload 0 /* this */
            getfield com.google.common.base.Converter$FunctionBasedConverter.forwardFunction:Lcom/google/common/base/Function;
            invokevirtual java.lang.Object.hashCode:()I
            bipush 31
            imul
            aload 0 /* this */
            getfield com.google.common.base.Converter$FunctionBasedConverter.backwardFunction:Lcom/google/common/base/Function;
            invokevirtual java.lang.Object.hashCode:()I
            iadd
            ireturn
        end local 0 // com.google.common.base.Converter$FunctionBasedConverter this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/common/base/Converter$FunctionBasedConverter<TA;TB;>;

  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.base.Converter$FunctionBasedConverter this
         0: .line 470
            new java.lang.StringBuilder
            dup
            ldc "Converter.from("
            invokespecial java.lang.StringBuilder.<init>:(Ljava/lang/String;)V
            aload 0 /* this */
            getfield com.google.common.base.Converter$FunctionBasedConverter.forwardFunction:Lcom/google/common/base/Function;
            invokevirtual java.lang.StringBuilder.append:(Ljava/lang/Object;)Ljava/lang/StringBuilder;
            ldc ", "
            invokevirtual java.lang.StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
            aload 0 /* this */
            getfield com.google.common.base.Converter$FunctionBasedConverter.backwardFunction:Lcom/google/common/base/Function;
            invokevirtual java.lang.StringBuilder.append:(Ljava/lang/Object;)Ljava/lang/StringBuilder;
            ldc ")"
            invokevirtual java.lang.StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
            invokevirtual java.lang.StringBuilder.toString:()Ljava/lang/String;
            areturn
        end local 0 // com.google.common.base.Converter$FunctionBasedConverter this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/common/base/Converter$FunctionBasedConverter<TA;TB;>;
}
Signature: <A:Ljava/lang/Object;B:Ljava/lang/Object;>Lcom/google/common/base/Converter<TA;TB;>;Ljava/io/Serializable;
SourceFile: "Converter.java"
NestHost: com.google.common.base.Converter
InnerClasses:
  private final FunctionBasedConverter = com.google.common.base.Converter$FunctionBasedConverter of com.google.common.base.Converter