2.7 Jb0130: java oop: a gentle introduction to methods in java  (Page 3/5)

Writing your own methods

As mentioned earlier, you can write your own methods in Java. I mention this here so you will know that it is possible. I will have more to say about writing your own methods in futuremodules.

Sample program

A complete listing of a sample program named SqRt01.java is provided in Listing 5 near the end of the lesson. A batch file that you can use to compile and run the program is provided in Listing 6 .

When you compile and run the program, the following output should appear on your computer screen:

As you will see shortly, these are the square root values respectively for 25.5 and 36.

Interesting code fragments

I will explain portions of this program in fragments. I will explain only those portions of the program that are germane to this module. Don't worry about the other details of the program. You will learn about those details infuture modules.

You may find it useful to open this lesson in another browser window so that you can easily scroll back and forth among the fragments while reading the discussion.

The first code fragment that I will explain is shown in Listing 1 .

What is the price of beans?

The code fragment shown in Listing 1 declares a variable named beans and assigns a value of 25.5 to the variable. (I briefly discussed the declaration of variables in a previous module. I will discuss them in more detail in a future module.)

What is that double thing?

In an earlier module, I declared a variable with a type named int . At that time, I explained that only integer values could be stored in that variable.

The variable named beans in Listing 1 is declared to be of the type double . I will explain the concept of data types in detail in a future module. Briefly, double means that you can store any numeric value in this variable, with or without adecimal part. In other words, you can store a value of 3 or a value of 3.33 in this variable, whereas a variable with a declared type of int won't accept a value of 3.33.

Every method has a name

Every method, every variable, and some other things as well have names. The names in Java are case sensitive . By case sensitive, I mean that the method named amethod is not the same as the method named aMethod .

A few words about names in Java

There are several rules that define the format of allowable names in Java. You can dig into this in more detail on the web if you like, but if you followthese two rules, you will be okay:

• Use only letters and numbers in Java names.
• Always make the first character a letter.

A standard method named sqrt

Java provides a Math library that contains many standard methods. Included in those methods is a method named sqrt that will calculate and return the square root of a number that is passed as a parameter when the method iscalled.

The sqrt method is called on the right-hand side of the equal sign (=) in the code fragment in Listing 2 .