Why does Java implicitly (without cast) convert a `long` to a `float`?

by

The same question could be asked of long to double – both conversions may lose information.

Section 5.1.2 of the Java Language Specification says:

Widening primitive conversions do not
lose information about the overall
magnitude of a numeric value. Indeed,
conversions widening from an integral
type to another integral type do not
lose any information at all; the
numeric value is preserved exactly.
Conversions widening from float to
double in strictfp expressions also
preserve the numeric value exactly;
however, such conversions that are not
strictfp may lose information about
the overall magnitude of the converted
value.

Conversion of an int or a long value
to float, or of a long value to
double, may result in loss of
precision-that is, the result may lose
some of the least significant bits of
the value. In this case, the resulting
floating-point value will be a
correctly rounded version of the
integer value, using IEEE 754
round-to-nearest mode (ยง4.2.4).

In other words even though you may lose information, you know that the value will still be in the overall range of the target type.

The choice could certainly have been made to require all implicit conversions to lose no information at all – so int and long to float would have been explicit and long to double would have been explicit. (int to double is okay; a double has enough precision to accurately represent all int values.)

In some cases that would have been useful – in some cases not. Language design is about compromise; you can’t win ’em all. I’m not sure what decision I’d have made…

More Related Contents:

  1. “Cast” a String Attribute to String Java [duplicate]
  2. Integer division: How do you produce a double?
  3. Explanation of ClassCastException in Java
  4. Casting variables in Java
  5. How do you cast a List of supertypes to a List of subtypes?
  6. What is the difference between up-casting and down-casting with respect to class variable
  7. Struts2 INPUT result: how does it work? How are conversion / validation errors handled?
  8. Safely casting long to int in Java
  9. Casting objects in Java
  10. Java converting Image to BufferedImage
  11. Convert boolean to int in Java
  12. How to insert a character in a string at a certain position?
  13. Java Class.cast() vs. cast operator
  14. What is the priority of casting in java?
  15. Cast Object to Generic Type for returning
  16. How to cast List to List
  17. How does Java Object casting work behind the scene? [duplicate]
  18. How to cast from List to double[] in Java?
  19. Why cannot cast Integer to String in java?
  20. Converting double to integer in Java
  21. Java: Casting from List to List when B implements A?
  22. Casting a class to an unrelated interface
  23. Explicit casting from super-class to sub-class
  24. Java: What’s the difference between autoboxing and casting?
  25. casting Arrays.asList causing exception: java.util.Arrays$ArrayList cannot be cast to java.util.ArrayList
  26. Casting rules for primitive types in java
  27. Casting LinkedHashMap to Complex Object
  28. com.google.gson.internal.LinkedTreeMap cannot be cast to my class [duplicate]
  29. Java casting order
  30. Cast via reflection and use of Class.cast() [duplicate]

Leave a Comment