Is there a Java equivalent or methodology for the typedef keyword in C

Question

Coming from a C and C   background  I found judicious use of typedef to be incredibly helpful   Do you know of a way to achieve similar functionality in Java  whether that be a Java mechanism  pattern  or some other effective way you have used

User · Accepted Answer

Java has primitive types  objects and arrays and that s it  No typedefs

User · Answer

Perhaps this could be another possible replace     Data public class MyMap        Delegate   lombok     private HashMap lt String  String gt  value

User · Answer

Really  the only use of typedef that carries over to Javaland is aliasing- that is  giving the same class multiple names  That is  you ve got a class  A  and you want  B  to refer to the same thing  In C    you d be doing  typedef B A    Unfortunately  they just don t support it  However  if you control all the types involved you CAN pull a nasty hack at the library level- you either extend B from A or have B implement A

User · Answer

There is no need for typedef in Java  Everything is an Object except for the primitives  There are no pointers  only references  The scenarios where you normally would use typedefs are instances in which you create objects instead

User · Answer

In some cases  a binding annotation may be just what you re looking for   https   github com google guice wiki BindingAnnotations  Or if you don t want to depend on Guice  just a regular annotation might do

User · Answer

Kotlin supports type aliases https   kotlinlang org docs reference type-aliases html  You can rename types and function types

User · Answer

If this is what you mean  you can simply extend the class you would like to typedef  e g    public class MyMap extends HashMap lt String  String gt

User · Answer

Typedef allows items to be implicitly assigned to types they are not  Some people try to get around this with extensions  read here at IBM for an explanation of why this is a bad idea   Edit  While strong type inference is a useful thing  I don t think  and hope we won t  see typedef rearing it s ugly head in managed languages  ever     Edit 2  In C   you can use a using statement like this at the top of a source file  It s used so you don t have to do the second item shown  The only time you see the name change is when a scope introduces a name collision between two types  The renaming is limited to one file  outside of which every variable parameter type which used it is known by its full name   using Path   System IO Path  using System IO

User · Answer

You could use an Enum  although that s semantically a bit different than a typedef in that it only allows a restricted set of values  Another possible solution is a named wrapper class  e g   public class Apple         public Apple Integer i  this i i        but that seems way more clunky  especially given that it s not clear from the code that the class has no other function than as an alias

User · Answer

There is no typedef in java as of 1 6  what you can do is make a wrapper class for what you want  since you can t subclass final classes  Integer  Double  etc

User · Answer

As noted in other answers  you should avoid the pseudo-typedef antipattern   However  typedefs are still useful even if that is not the way to achieve them   You want to distinguish between different abstract types that have the same Java representation   You don t want to mix up strings that are passwords with those that are street addresses  or integers that represent an offset with those with those that represent an absolute value   The Checker Framework enables you to define a typedef in a backward-compatible way   I works even for primitive classes such as int and final classes such as String   It has no run-time overhead and does not break equality tests   Section Type aliases and typedefs in the Checker Framework manual describes several ways to create typedefs  depending on your needs

User · Answer

As others have mentioned before   There is no typedef mechanism in Java   I also do not support  fake classes  in general  but there should not be a general strict rule of thumb here   If your code for example uses over and over and over a  generic based type  for example    Map lt String  List lt Integer gt  gt     You should definitely consider having a subclass for that purpose   Another approach one can consider  is for example to have in your code a deceleration like      Alias Map lt String  List lt Integer gt  gt   NameToNumbers    And then use in your code NameToNumbers and have a pre compiler task  ANT Gradle Maven  to process and generate relevant java code   I know that to some of the readers of this answer this might sound strange  but this is how many frameworks implemented  annotations  prior to JDK 5  this is what project lombok is doing and other frameworks

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