Abstraction in java

abstraction

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Java Abstraction:

1.Is one which make a class abstract in object orient programming. It means it provides only essential features for a certain program when needed.

2. Abstract class  cannot be instantiated.

3.Abstract methods will be declared in parent class.

4.If a class has abstract method .Its class should also been  declared as abstract.

Example:

{code type=”java”}
public abstract class Employee
{
private String name;
private String address;
private int number;
public Employee(String name, String address, int number)
{
System.out.println(“Constructing an Employee”);
this.name = name;
this.address = address;
this.number = number;
}
public double computePay()
{
System.out.println(“Inside Employee computePay”);
return 0.0;
}
public void mailCheck()
{
System.out.println(“Mailing a check to ” + this.name
+ ” ” + this.address);
}
public String toString()
{
return name + ” ” + address + ” ” + number;
}
public String getName()
{
return name;
}
public String getAddress()
{
return address;
}
public void setAddress(String newAddress)
{
address = newAddress;
}
public int getNumber()
{
return number;
}
}

{/code}
This above code is an example to abstract class,where abstract keyword appears before class keyword in class declaration.

5. Abstract Class can be inherited.

Abstract Method:

Abstract method is one where you can use whenever you look to define a method in a derived class.You can make that method as abstract in parent class with only declaration prefixed with keyword abstract.
{code type=java}
public abstract class Employee
{
private String name;
private String address;
private int number;

public abstract double computePay();

//Remainder of class definition
}
public class Salary extends Employee
{
private double salary; // Annual salary

public double computePay()
{
System.out.println(“Computing salary pay for ” + getName());
return salary/52;
}

//Remainder of class definition
}
{/code}

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