http://fastutil.di.unimi.it/: fastutil extends the Java Collections Framework by providing type-specific maps, sets, lists and priority queues with a small memory footprint and fast access and insertion; provides also big (64-bit) arrays, sets and lists, and fast, practical I/O classes for binary and text files.
  • Sebastiano Vigna 
public interface it.unimi.dsi.fastutil.doubles.Double2ObjectMap$Entry<V> extends java.util.Map$Entry<java.lang.Double, V>
  minor version: 0
  major version: 59
  flags: flags: (0x0601) ACC_PUBLIC, ACC_INTERFACE, ACC_ABSTRACT
  this_class: it.unimi.dsi.fastutil.doubles.Double2ObjectMap$Entry
  super_class: java.lang.Object
{
  public abstract double getDoubleKey();
    descriptor: ()D
    flags: (0x0401) ACC_PUBLIC, ACC_ABSTRACT

  public java.lang.Double getKey();
    descriptor: ()Ljava/lang/Double;
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=2, locals=1, args_size=1
        start local 0 // it.unimi.dsi.fastutil.doubles.Double2ObjectMap$Entry this
         0: .line 672
            aload 0 /* this */
            invokeinterface it.unimi.dsi.fastutil.doubles.Double2ObjectMap$Entry.getDoubleKey:()D
            invokestatic java.lang.Double.valueOf:(D)Ljava/lang/Double;
            areturn
        end local 0 // it.unimi.dsi.fastutil.doubles.Double2ObjectMap$Entry this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lit/unimi/dsi/fastutil/doubles/Double2ObjectMap$Entry<TV;>;
    RuntimeVisibleAnnotations: 
      java.lang.Deprecated()

  public java.lang.Object getKey();
    descriptor: ()Ljava/lang/Object;
    flags: (0x1041) ACC_PUBLIC, ACC_BRIDGE, ACC_SYNTHETIC
    Code:
      stack=1, locals=1, args_size=1
         0: .line 1
            aload 0
            invokeinterface it.unimi.dsi.fastutil.doubles.Double2ObjectMap$Entry.getKey:()Ljava/lang/Double;
            areturn
      LocalVariableTable:
        Start  End  Slot  Name  Signature
}
Signature: <V:Ljava/lang/Object;>Ljava/lang/Object;Ljava/util/Map$Entry<Ljava/lang/Double;TV;>;
SourceFile: "Double2ObjectMap.java"
NestHost: it.unimi.dsi.fastutil.doubles.Double2ObjectMap
InnerClasses:
  public abstract Entry = it.unimi.dsi.fastutil.doubles.Double2ObjectMap$Entry of it.unimi.dsi.fastutil.doubles.Double2ObjectMap
  public abstract Entry = java.util.Map$Entry of java.util.Map