Computer programming 2 Lesson 15

Computer
Programming 2
Lesson 15 – Java – Methods
Prepared by: Analyn G. Regaton

What is a
method?
In mathematics, we might have studied about functions.
For example, f(x) = x2 is a function that returns a squared
value of x.
If x = 2, then f(2) = 4
If x = 3, f(3) = 9
and so on.
Similarly, in computer programming, a function is a block
of code that performs a specific task.
In object-oriented programming, the method is a jargon
used for function. Methods are bound to a class and they
define the behavior of a class.

Types of Java
methods
Standard Library
Methods
User-defined Methods
Standard Library Methods
The standard library methods are built-in methods in Java
that are readily available for use. These standard libraries
come along with the Java Class Library (JCL) in a Java
archive (*.jar) file with JVM and JRE.
For example,
 print() is a method of java.io.PrintSteam.
The print("...") method prints the string inside
quotation marks.
 sqrt() is a method of Math class. It returns the square
root of a number.
Here's a working example:
public class Main {
public static void main(String[] args) {
// using the sqrt() method
System.out.print("Square root of 4 is: " + Math.sqrt(4));
}
}
Output:
Square root of 4 is: 2.0

Types of Java
methods
Standard Library
Methods
User-defined Methods
User-defined Method
We can also create methods of our own choice to perform some task.
Such methods are called user-defined methods.
How to create a user-defined method?
Here is how we can create a method in Java:
public static void myMethod() {
System.out.println("My Function called");
}
Here, we have created a method named myMethod(). We can see that we
have used the public, static and void before the method name.
 public - access modifier. It means the method can be accessed from
anywhere. static - It means that the method can be accessed without
any objects.
 void - It means that the method does not return any value. We will
learn more about this later in this tutorial.
This is a simple example of how we can create a method. However, the
complete syntax of a method definition in Java is:
modifier static returnType nameOfMethod (parameters) {
// method body
}

Definition of
Terms
Modifier
Public
Private
Static keyword
For example, the sqrt() method of standard Math class is
static. Hence, we can directly call Math.sqrt() without
creating an instance of Math class.
returnType Type of value
returns
 If the method does not return a value, its return
type is void.
A method can return native data types (int, float, double, etc), native objects
(String, Map, List, etc), or any other built-in and user-defined objects.

Definition of
Terms
nameOf
Method
identifier
Particular method
Static keyword
For example
calculateArea(), display(), and so on
parameters(
arguments)
Values passed to a
method
Method
body
Statements
enclosed { }

How to call
java method?
Here's how
myMethod();
This statement calls myMethod() method that was declared earlier.
Working of the method call in Java
•While executing the program code, it encounters myFunction(); in the code.
•The execution then branches to the myFunction() method and executes code inside the
body of the method.
•After the execution of the method body, the program returns to the original state and
executes the next statement after the method call.

Example
program
Let's see how we can use methods in a Java program.
class Main {
System.out.println("About to encounter a method.");
// method call
myMethod();
System.out.println("Method was executed successfully!");
}
// method definition
private static void myMethod(){
System.out.println("Printing from inside myMethod()!");
}
}
Output:
About to encounter a method.
Printing from inside myMethod().
Method was executed successfully!

Another
example
class Main {
// create object of the Output class
Output obj = new Output();
System.out.println("About to encounter a method.");
// calling myMethod() of Output class
obj.myMethod();
System.out.println("Method was executed successfully!");
}
}
class Output {
// public: this method can be called from outside the class
public void myMethod() {
System.out.println("Printing from inside myMethod().");
}
}
Output:
About to encounter a method.
Printing from inside myMethod().
Method was executed successfully!
Since the method is not static, it is called using the object obj of the class.
obj.myMethod();

Method
Arguments
and Return
Value
Let's take an example of a method returning a
value.
class SquareMain {
int result;
// call the method and store returned value
result = square();
System.out.println("Squared value of 10 is: " +
result);
}
public static int square() {
// return statement
return 10 * 10;
}
}
Output:
Squared value of 10 is: 100

Example:
Method
Accepting
Arguments
and Returning
Value
public class Main {
int result, n;
n = 3;
result = square(n);
System.out.println("Square of 3 is: " +
result);
n = 4;
result = square(n);
System.out.println("Square of 4 is: " +
result);
}
// method
static int square(int i) {
return i * i;
}
}
Output:

We can also
pass more
than one
argument to
the Java
method by
using
commas.
For example,
public class Main {
public static int getIntegerSum (int i, int j) {
return i + j;
}
public static int multiplyInteger (int x, int y) {
return x * y;
}
// calling methods
System.out.println("10 + 20 = " + getIntegerSum(10, 20));
System.out.println("20 x 40 = " + multiplyInteger(20, 40));
}
}
Output:
10 + 20 = 30
20 x 40 = 800

What are the
advantages of
using
methods?
1. The main advantage is code reusability.
public class Main {
// method defined
private static int getSquare(int x){
return x * x;
}
for (int i = 1; i <= 5; i++) {
// method call
int result = getSquare(i);
System.out.println("Square of " + i + " is: " + result);
}
}
}
Output:
Square of 1 is: 1
Square of 2 is: 4
Square of 3 is: 9
Square of 4 is: 16
Square of 5 is: 25
2. Methods make code more readable and easier to debug.

Computer programming 2 Lesson 15

More Related Content

What's hot (20)

Similar to Computer programming 2 Lesson 15 (20)

More from MLG College of Learning, Inc (20)

Recently uploaded (20)

Computer programming 2 Lesson 15