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Programming in Java Netbeans - A Step by Step Tutorial for Beginners: Lesson 25

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Lesson 25: User defined methods (UDMs) in Java

Over the previous lessons on Java methods, we have been dealing with Java inbuilt methods only, that is, methods which have already been created for us and so all we need to do is to call and use them.

In this particular lesson and the following lesson, we shall learn how we can define and create our own methods in Java programming language. Methods defined and created by user or programmer, other than those that ships in with the development environment, are referred to us User Defined Methods (UDMs).


The Structure of a Method in Java

A method is just a group of instructions that are coded and given a name. When a method is called by its name in a program, the instructions are executed to accomplish an action.

Take an example of the Java toUpperCase() method that we discussed in Lesson 19, the instructions that are contained in this method checks whether the character or string passed to it is in uppercase, if not, then it returns the character or string in uppercase.

Usually, a method has two parts; the method header and the body. The method header contains the following:

1. Method return type

Method return type specifies what type of value, if any, that the method will return when executed. The return value can be of type int, double, string, etc.

2. Method name

Method name is any qualified name that descriptively suits the method. It is a good practice to name a method with a meaningful name that describes its function.

3. Values passed to the method (Parameters)

This section of a method header is optional as some methods do not require values to be passed to them. If the method require value or values to be passed, then those values are passed in this section. Passed values can be of type int, double, string, float etc. Values passed to a method are called Parameters.

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The method body contains the actual instructions that will be executed when the method is called. The code can be a single line or multiple lines of instructions. See the image below about the structure of a method.

The Structure of a Method in Java

The Structure of a Method in Java

In the above image about the structure of a method, the return type is int, the method name is sum and method parameters are x and y. To separate the method header and method body, we use a pair of curly braces { }. Notice the method above is supposed to receive two values (x and y), sum them and return the total as z.

The keyword return returns a value from the method after executing the code. The returned value must be of the same type as the method return type in the method header. So the return value cannot be of string type if the method return type is of int type.

In some cases, the method may not return any value; such methods are called void methods and the method header starts with the keyword “void”. See an example below of a void method that only prints a string on the console. The method does not take any parameter either as you can see the round brackets are empty.


Having knowledge of how methods work in Java is the first step in creating User Defined Methods. Knowing how to declare parameters, pass parameters and call methods is the next step. In the next lesson, we shall look at how we can implement User Defined Methods in Java programming languages.

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Danson Wachira (author) from Nairobi, Kenya on September 25, 2012:

Thanks teaches12345 for the visit and the kind words in your comment, i feel motivated to go on and on. Enjoy your day.

Dianna Mendez on September 24, 2012:

Keep the lessons coming. They are ones that are going to hit the users with great information on Java.

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