Is it possible to define custom types in java that work with primitives?

Question

For example the following is syntactically correct code

Double number = 10.0;

Is it possible to define my own class such as Price

Price myPrice = 10.0;

Actually compiles ?

Solution 1

Auto-boxing and auto-unboxing only works with primitives. The concept you are talking about is similar to C++ conversions. Unfortunately, there is no such thing in Java. The best you can do is

Price myPrice = new Price(10.0);

Solution 2

No, you can't define your own primitive types for numerical quantities.

Declaring Price myPrice means that the variable myPrice will be of type Price and will be used to as its instance.

You can have following valid.

Suppose you declare variable myPrice of type Price. Some instance variables can be accessed via that myPrice reference.

Price myPrice = new Price();
myPrice.value = 10.0;
myPrice.currency = "Dollar"; 
etc ....

Comments

[Joachim Sauer]

Strictly speaking primitives can't be instantiated at all, they are not objects. Auto-boxing allows implicit creation of primitive wrapper objects in some cases, however.

[Saurabh Gokhale]

@Joachim : value and currency are the instance variables of Price class. So they can be accessed via myPrice reference

[f1sh]

but there's no myPrice = new Price(); so line 2 will throw a NPE. That's what Joachim meant. EDIT: answered too late :-/

[Saurabh Gokhale]

^ Yes ... Oops. Missed that. :-)