What are symbolic constants and how they are useful in developing programs?

Answer 1

symbolic constants are named constants

like :

final double PI = 3.14 ;

They are constants because of the 'final' keywords, so they canNOT be reassigned a new value after being declared as final

And they are symbolic , because they have a name

A NON symbolic constant is like the value of '2' in expression

int foo = 2 * 3

Answer given By Sushil Mittal..........

Answer 2

Suppose that you write a large program that uses the sales tax percentage in many places. Then, after you've been happily using your program for a few months, the state suddenly decides to raise the sales tax to seven percent. In order to get your program working again, you have to go through every line of code, looking for the .06 values that represent the sales tax and changing them to .07. Such a modification can be a great deal of work in a large program. Worse, you may miss one or two places in the code that need to be changed, leaving your program with some serious bugs.

To avoid these situations, programmers often use something called symbolic constants, which are simply words that represent values in a program. In the case of your sales tax program, you could choose a word like SALESTAX (no spaces) to represent the current sales tax percentage for your state. Then, at the beginning of your program, you set SALESTAX to be equal to the current state sales tax. In the Java language, such a line of program code might look like this:

final float SALESTAX = 0.06;

In the preceding line, the word final tells Java that this data object is going to be a constant. The float is the data type, which, in this case, is a floating point. The word SALESTAX is the symbolic constant. The equals sign tells Java that the word on the left should be equal to the value on the right, which, in this case, is 0.06.

After defining the symbolic constant SALESTAX, you can rewrite any lines that use the current sales tax value to use the symbolic constant rather than the hard-coded value. For example, the calculation for the sales tax on that $12.00 purchase might now look something like this:

tax = 12 * SALESTAX;

Now, when your state changes the sales tax to 7 percent, you need only change the value you assign to the symbolic constant and the rest of the program automatically fixes itself. The change would look like this:

final float SALESTAX = 0.07;