Java Methods

1. Java Methods
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2. Outline
▪ Class Instance Methods
▪ Static Methods
▪ Methods with no Parameters
▪ Methods with Parameters
▪ Methods with Return Value
▪ Method Overloading
▪ Method Overriding
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3. Class Instance Methods
▪ Instance methods require an object of its class to be created
before it can be called.
▪ To invoke an instance method, create an object of the class
within which it is defined.
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4. Class Instance Methods
▪ Instance methods require an object of its class to be created before it can
be called.
▪ To invoke an instance method, create an object of the class within which it
is defined.
▪ Instance methods belong to the object of the class not to the class, they
can be called after creating the object of the class.
▪ Every individual object create from the class has its own copy of the
instance methods of that class.
▪ Every individual Object created from the class has its own copy of the
instance method(s) of that class.
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5. Example
public class Student {
private String name;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
public class StudentRunner {
public static void main(String[] args) {
Student student = new Student();
student.setName("Me");
student.getName();
}
}
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6. Static Method
▪Static methods are the methods in Java that can be called without creating
an object of class.
▪ They are referenced by the class name itself or reference to the object of
that class.
▪ Static methods are associated to the class in which they reside i.e. they can
be called even without creating an instance of the class, i.e
ClassName.methodName(args).
▪ They are designed with aim to be shared among all objects created from
the same class.
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7. Example
class Student{
public static String studentName = "";
public static void getName(String name){
studentName = name;
}
}
public class StudentRunner {
public static void main (String[] args) {
// Accessing the static method getName() and
// field by class name itself.
Student.getName("Me");
System.out.println(Student.studentName);
// Accessing the static method getName() by using Object's
reference.
Student student = new Student();
student.getName("You");
System.out.println(student.studentName);
}
}
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8. Method with no Parameter
▪ Method that does not accept any arguments.
public class MathDemo {
void areaOfcircle() {
System.out.print("enter the radius :");
Scanner s = new Scanner(System.in);
float r = s.nextFloat();
float ar;
ar = (r * r) * 22 / 7;
System.out.println("area of the circle is :
"+ar+" sq units.");
} }
public class MathDemoRunner {
public static void main(String[] args) {
MathDemo obj = new MathDemo();
obj.areaOfCircle();
} }
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9. Method with Parameters
▪ Method that accepts arguments.
public class MathDemo {
void areaOfCircle(float r, float ar)
{
ar = (r * r) * 22 / 7;
System.out.println("area of the circle is : "+ar+"
sq units.");
}
}
public static void main(String[] args) {
MathDemo obj = new MathDemo();
obj.areaOfCircle(12, 12);
}
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10. Methods with Return Value
▪ Java requires that a method declare the data type of the value that it returns.
▪ If a method does not return a value, it must be declared to return void.
public class MathDemo {
static int myMethod(int x) {
return 5 + x;
}
public static void main(String[] args) {
System.out.println(myMethod(3));
}
}
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11. Method Overloading
▪ Method overloading
▪ allows a method with the same name but different parameters, to have different
implementations and return values of different types
▪ can be used when the same operation has different implementations.
▪ Overloaded methods have the following properties:
▪ the same name
▪ different parameters
▪ return types can be different or the same
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12. Method Overloading
public class MathDemo {
// Overloaded sum().
// This sum takes two int parameters
public int sum(int x, int y) {
return (x + y);
}
// Overloaded sum(). This sum takes three int
parameters
public int sum(int x, int y, int z) {
return (x + y + z);
}
// Overloaded sum(). This sum takes two double
parameters
public double sum(double x, double y) {
return (x + y); }
// Driver code
public static void main(String args[]) {
MathDemo s = new MathDemo();
System.out.println(s.sum(10, 20));
System.out.println(s.sum(10, 20, 30));
System.out.println(s.sum(10.5, 20.5));
}
}
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13. Method Overriding
▪ Method Overriding in Java is a condition when a subclass has the same method as
declared in the parent class.
▪ A parent class can be called an overridden method.
▪ In object-oriented programming, the feature of overriding is used to provide a class,
subclass or a child class to use a method that is already used by parent class to have a
specific implementation.
▪ Method overriding in Java programming occurs when the method in the subclass has the
same return type, or parameters, name or signature as the parent class.
▪ Method overriding is the method by which Java can support runtime polymorphism.
▪ Basically, the method to execute is chosen on the basis of the type of object and not on
the type of reference variable.
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14. Method Overriding
public class Parent {
void methodOfParentClass() {
System.out.println("Parent's method()");
} }
public class Child extends Parent {
@Override
void methodOfParentClass() {
System.out.println("Child's method()");
} }
public class MethodOverriding {
public static void main(String[] args) {
Parent obj1 = new Parent();
obj1.methodOfParentClass();
Parent obj2 = new Child();
obj2.methodOfParentClass();
}
}
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