Conversion and coercion in Java

For 2023 (and 2024 ...) - we are now fully retired from IT training.
We have made many, many friends over 25 years of teaching about Python, Tcl, Perl, PHP, Lua, Java, C and C++ - and MySQL, Linux and Solaris/SunOS too. Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own risk.

Lisa and I (Graham) now live in what was our training centre in Melksham - happy to meet with former delegates here - but do check ahead before coming round. We are far from inactive - rather, enjoying the times that we are retired but still healthy enough in mind and body to be active!

I am also active in many other area and still look after a lot of web sites - you can find an index ((here))

The accuracy and conversion of primitive arithmetic variables in Java is something that I'm questioned on regularly.

Ideally in Java, you'll perform arithmetic on two pieces of data of an identical type, and the result returned will be of the same type. However, if you perform a calculation on two different types the "least accurate" will be coerced up to the accuracy of the second. For example, integer is coerced to float which in turn may be coerced to a double.

What does this mean?

Calculation	types	Result type	Stored in variable of type
a = 5.0/2	D/I	D	D
b = 5/2.0F	I/F	F	F or D
c = 5/2	I/I	I	I L F or D
d = 5/2.0	I/D	D	D

I - int
L - long
F - float
D - double

Note that a constant such as 2.0 id double, whereas 2.0f or 2.0F is float.

If you wish to save a result into a "less accurate" variable, you may do so by casting it. For example
a = (float) (5/2.0)
will convert an integer up to a double for the division through coersion and will then cast it back to a float before saving it in the variable a

Select here for a download of my "variables in Java" training notes released under an open training notes license. Further examples of simple variable use in Java can be found in our modules resource centre.
(written 2004-11-22, updated 2006-06-05)

Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles

J703 - Java - Variables
  [1448] Question on division (Java) - Also Perl, PHP, Python ... - (2007-11-28)
  [2148] Variable scope in Java Servlets and other web applications - (2009-05-01)
  [2153] Class Loading and Variable Conversion in Java - (2009-05-02)
  [3038] Setting up individual variables, and arrays, in Java - some commented examples - (2010-11-09)
  [3041] Java - basic rules for arithmetic, variables and conversion - (2010-11-10)
  [3278] Do I need to initialise variables - programming in C, C++, Perl, PHP, Python, Ruby or Java. - (2011-05-05)
  [3365] Turning bright delegates into bright and knowledgable ones - (2011-07-21)
  [3917] BODMAS - the order a computer evaluates arithmetic expressions - (2012-11-09)
  [4324] Learning to program - variables and constants - (2014-11-22)
  [4345] Incrementing a variable in Java - Pre and Post Increment - (2014-12-08)

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Thanksgiving dinner
Spelling and grammar
Trawling our site to prevent student copying
Technical Weekend / Geekmas
Conversion and coercion in Java
Feedback shows the tip of an iceberg
Staff theft
PHP v Java
Short underground journeys and a PHP book
Passing arrays to procs in Tcl

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