Method

Methods can be used to define reusable code and organize and simplify coding.

Why need a method?

Suppose that you need to find the sum of integers from 1 to 10 , from 20 to 37 , and from 35 to 49 , respectively.

You may write the code as follows:

int sum = 0;
for (int i = 1; i <= 10; i++){
    sum += i;
    System.out.println("Sum from 1 to 10 is " + sum);
}
​
​
sum = 0;
for (int i = 20; i <= 37; i++){
    sum += i;
    System.out.println("Sum from 20 to 37 is " + sum);
}
​
​
sum = 0;
for (int i = 35; i <= 49; i++){
    sum += i;
    System.out.println("Sum from 35 to 49 is " + sum);
}

Wouldn’t it be nice if we could write the common code once and reuse it? We can do so by defining a method and invoking it.

Think about the code below:

public void sumNumber(int i,int j){
    int sum =0;
    for(int counter=i;counter<=j;counter++){
        sum=sum+counter;
    }
    return sum;
}

Now all you need to do is calling this method three times:

sumNumber(1,10);
sumNumber(20,37);
sumNumber(35,49);

See, with just a couple lines of code we achieve the same goal.

That’s the magic of Method！

What are the advantages of using methods?

• The main advantage is code reusability. You can write a method once, and use it multiple times. You do not have to rewrite the entire code each time. Think of it as, “write once, reuse multiple times.”

• Methods make code more readable and easier to debug. For example, getSalaryInformation() method is so readable, that we can know what this method will be doing than actually reading the lines of code that make this method.

Types of Java methods

Depending on whether a method is defined by the user, or available in standard library, there are two types of methods:

• Standard Library Methods

• User-defined 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("...") prints the string inside quotation marks.

• sqrt() is a method of Math class. It returns square root of a number.

Here’s an working example:

public class Numbers {
    public static void main(String[] args) {
        System.out.print("Square root of 4 is: " + Math.sqrt(4));
    }
}

When you run the program, the output will be:

Square root of 4 is: 2.0

User-defined Method

You can also define methods inside a class as per your wish. Such methods are called user-defined methods.We will talk it in the later chapter.