1. Constants in Java
Why and How
Copyright © Curt Hill

2. Introduction There are two kinds of constants in Java
Literals
Named constants
We will see the whys and wherefores now
Copyright © Curt Hill

3. Literal constants We have seen the following fours kinds of constants:
-45 (int)
2.3 (floating point of type double)
1E4 (float)
‘A’ (char)
“Hi” (string)
Normally, merely inspecting the constant will tell you its type, as well as its value
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4. Literals Continued
What do we do to set the constant to something other than a standard int or double?
We can use a suffix to tell it the type
The L or l indicates that it is long
The U or u indicates unsigned
Floating point constants are by default double
Suffix of F or f makes it a float, L a long double
You may also use binary, octal or hexadecimal constants but we do not need to do that here
Copyright © Curt Hill

5. Literal Problems
However, literal constants have the following problems that sometimes need to be dealt with
We have to retype them each time
This is a problem with high precision constants like PI
Opportunities for typing errors
Just remembering what the 14 digit value is
We have to remember what they represent
Small integer constants tend to get confused with one another
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6. Example:
Suppose that I am a manager and I have 5 people who work 5 days a week and 8 hours a day
Thus the number of manhours is: workhours = 5 * 5 * 8;
Now we will try something new, four ten hour days per week
I use my text editor and change all 5s to 4s and all 8s to 10s
We now get workhours = 4 * 4 * 10;
The problem with the above expression is that the 5 and 8 have no inherent meaning
Copyright © Curt Hill

7. Alternative
It would be better to say: int people = 5, dayperweek = 5, hoursperday = 8; ... workhours = people * dayperweek * hoursperday;
Unfortunately that leads to a problem:
An inadvertent assignment to one of the variables
The solution is that we would like to be able to name constants, just like we name variables but without possibility of assignment
Copyright © Curt Hill

8. Final Keyword
A feature that allows constants in Java is the final qualifier:
final float pi = ;
Any attempt to assign to this will result in an error
The float type determines the precision used
Copyright © Curt Hill

9. Discussion The final is a keyword that prefixes the declaration
This may be used anywhere a variable may be declared
The declaration must have an initialization
Copyright © Curt Hill

10. Conclusion The reserved word final makes a variable into a constant
Use to make the code more readable
Shortens the typing for constants with many digits
Prevents using global replaces from doing too much
Copyright © Curt Hill