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. 
public interface com.google.common.base.Function<F, T> extends java.util.function.Function<F, T>
  minor version: 0
  major version: 59
  flags: flags: (0x0601) ACC_PUBLIC, ACC_INTERFACE, ACC_ABSTRACT
  this_class: com.google.common.base.Function
  super_class: java.lang.Object
{
  public abstract T apply();
    descriptor: (Ljava/lang/Object;)Ljava/lang/Object;
    flags: (0x0401) ACC_PUBLIC, ACC_ABSTRACT
    Signature: (TF;)TT;
    RuntimeInvisibleAnnotations: 
      com.google.errorprone.annotations.CanIgnoreReturnValue()
    RuntimeVisibleTypeAnnotations: 
      METHOD_FORMAL_PARAMETER
        org.checkerframework.checker.nullness.qual.Nullable()
      METHOD_RETURN
        org.checkerframework.checker.nullness.qual.Nullable()
    MethodParameters:
       Name  Flags
      input  

  public abstract boolean equals(java.lang.Object);
    descriptor: (Ljava/lang/Object;)Z
    flags: (0x0401) ACC_PUBLIC, ACC_ABSTRACT
    RuntimeVisibleTypeAnnotations: 
      METHOD_FORMAL_PARAMETER
        org.checkerframework.checker.nullness.qual.Nullable()
    MethodParameters:
        Name  Flags
      object  
}
Signature: <F:Ljava/lang/Object;T:Ljava/lang/Object;>Ljava/lang/Object;Ljava/util/function/Function<TF;TT;>;
SourceFile: "Function.java"
    RuntimeVisibleAnnotations: 
      java.lang.FunctionalInterface()
    RuntimeInvisibleAnnotations: 
      com.google.common.annotations.GwtCompatible()