What is a method?
A method is a block of code or collection of statements or a set of code grouped together to perform a certain task or operation. It is used to achieve the reusability of code. We write a method once and use it many times. We do not require to write code again and again. It also provides the easy modification and readability of code, just by adding or removing a chunk of code. The method is executed only when we call or invoke it.
Method Declaration
The method declaration provides information about method attributes, such as visibility, return-type, name, and arguments. It has six components that are known as method header, as we have shown in the following figure.
Method Signature: Every method has a method signature. It is a part of the method declaration. It includes the method name and parameter list.
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Access Specifier: Access specifier or modifier is the access type of the method. It specifies the visibility of the method. Java provides four types of access specifier:
- Public: The method is accessible by all classes when we use public specifier in our application.
- Private: When we use a private access specifier, the method is accessible only in the classes in which it is defined.
- Protected: When we use protected access specifier, the method is accessible within the same package or subclasses in a different package.
- Default: When we do not use any access specifier in the method declaration, Java uses default access specifier by default. It is visible only from the same package only.
Return Type: Return type is a data type that the method returns. It may have a primitive data type, object, collection, void, etc. If the method does not return anything, we use void keyword.
Method Name: It is a unique name that is used to define the name of a method. It must be corresponding to the functionality of the method. Suppose, if we are creating a method for subtraction of two numbers, the method name must be subtraction(). A method is invoked by its name.
Parameter List: It is the list of parameters separated by a comma and enclosed in the pair of parentheses. It contains the data type and variable name. If the method has no parameter, left the parentheses blank.
Method Body: It is a part of the method declaration. It contains all the actions to be performed. It is enclosed within the pair of curly braces.
Naming a Method
While defining a method, remember that the method name must be a verb and start with a lowercase letter. If the method name has more than two words, the first name must be a verb followed by adjective or noun. In the multi-word method name, the first letter of each word must be in uppercase except the first word. For example:
Single-word method name: sum(), area()
Multi-word method name: areaOfCircle(), stringComparision()
It is also possible that a method has the same name as another method name in the same class, it is known as method overloading.
Types of Method
There are two types of methods in Java:
- Predefined Method
- User-defined Method
Predefined Method
In Java, predefined methods are the method that is already defined in the Java class libraries is known as predefined methods. It is also known as the standard library method or built-in method. We can directly use these methods just by calling them in the program at any point. Some pre-defined methods are length(), equals(), compareTo(), sqrt(), etc. When we call any of the predefined methods in our program, a series of codes related to the corresponding method runs in the background that is already stored in the library.
Ex:
1 2 3 4 5 6 | public class Demo { public static void main(String[] args) { // using the max() method of Math class System.out.print("The maximum number is: " + Math.max(9,7)); } } |
Output:
1 | The maximum number is: 9 |
In the above example, we have used three predefined methods main(), print(), and max().
User-defined Method
The method written by the user or programmer is known as a user-defined method. These methods are modified according to the requirement.
Create a User-defined Method
Ex:
1 2 3 4 5 6 7 8 | //user defined method public static void findEvenOdd(int num) { //method body if(num%2==0) System.out.println(num+" is even"); else System.out.println(num+" is odd"); } |
We have defined the above method named findevenodd(). It has a parameter num of type int. The method does not return any value that’s why we have used void. The method body contains the steps to check the number is even or odd. If the number is even, it prints the number is even, else prints the number is odd.
Call or Invoke a User-defined Method
In the above example, we have declared a method named findEvenOdd(). Now, to use the method, we need to call it.
Ex:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 | public class Main { //user defined method public static void findEvenOdd(int num) { //method body if(num % 2 == 0) System.out.println(num+" is even"); else System.out.println(num+" is odd"); } //main method public static void main(String[] args) { int a = 40; //call the method findEvenOdd(a); } } |
Output:
1 | 40 is even |
Static Method
A method that has static keyword is known as static method. In other words, a method that belongs to a class rather than an instance of a class is known as a static method. We can also create a static method by using the keyword static before the method name.
The main advantage of a static method is that we can call it without creating an object. It can access static data members and also change the value of it. It is used to create an instance method. It is invoked by using the class name. The best example of a static method is the main() method.
Ex:
1 2 3 4 5 6 7 8 9 | public class Display { public static void main(String[] args) { show(); } static void show() { System.out.println("It is an example of static method."); } } |
Output:
1 | It is an example of a static method. |
Instance Method
The method of the class is known as an instance method. It is a non-static method defined in the class. Before calling or invoking the instance method, it is necessary to create an object of its class. Let’s see an example of an instance method.
Ex:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 | public class InstanceMethodExample { public static void main(String [] args) { //Creating an object of the class InstanceMethodExample obj = new InstanceMethodExample(); //invoking instance method System.out.println("The sum is: "+obj.add(12, 13)); } int s; //user-defined method because we have not used static keyword public int add(int a, int b) { s = a+b; //returning the sum return s; } } |
Output:
1 | The sum is: 25 |
There are two types of instance method:
- Accessor Method
- Mutator Method
Accessor Method: The method(s) that reads the instance variable(s) is known as the accessor method. We can easily identify it because the method is prefixed with the word get. It is also known as getters. It returns the value of the private field. It is used to get the value of the private field.
Ex:
An error has occurred. Please try again later. |
Mutator Method: The method(s) read the instance variable(s) and also modify the values. We can easily identify it because the method is prefixed with the word set. It is also known as setters or modifiers. It does not return anything. It accepts a parameter of the same data type that depends on the field. It is used to set the value of the private field.
Ex:
1 2 3 | public void setRoll( int roll ) { this.roll = roll; } |
Ex of accessor and mutator method:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 | public class Student { private int roll; private String name; public int getRoll() { //accessor method return roll; } public void setRoll(int roll) { //mutator method this.roll = roll; } public String getName() { //accessor method return name; } public void setName(String name) { //mutator method this.name = name; } public void display() { System.out.println("Roll no.: "+roll); System.out.println("Student name: "+name); } } |
Abstract Method
The method that does not has method body is known as abstract method. In other words, without an implementation is known as abstract method. It always declares in the abstract class. It means the class itself must be abstract if it has abstract method. To create an abstract method, we use the keyword abstract.
Syntax:
abstract void method_name();
Ex:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 | abstract class Main { //abstract class //abstract method declaration abstract void display(); } public class MyClass extends Main { //method impelmentation void display() { System.out.println("Abstract method?"); } public static void main(String args[]) { //creating object of abstract class Main obj = new MyClass(); //invoking abstract method obj.display(); } } |
Output:
1 | Abstract method... |
Factory method
It is a method that returns an object to the class to which it belongs. All static methods are factory methods.
Ex:
1 | NumberFormat obj = NumberFormat.getNumberInstance(); |
