Rabu, 29 Oktober 2008
Inheritance involves creating new classes from the existing ones. it provides the ability to take the data and methods from an existing class and derive a new class. The keyword extends is used to inherit data and methods from a existing class. the extends keyword is used as
class New_Class extends Old_Class { ....... }
The inherited methods and data are those that are declared public or protected inside the super class. Using(Extending) same Engine.
Note: private members are not inherited. Here key is private
Java Access Modifiers Lesson
Eg How Inheritance works.
class Add
{
int x;
int y;
public int Add_xy()
{
int sum=0;
sum=x+y;
return sum;
}
}
class Sub extends Add
{
public int Sub_xy()
{
int sub;
sub=x-y;
return sub;
}
}
class Inheritance
{
pubic static void main(String args[])
{
Sub sub_obj=new Sub();
sub_obj.x=10;
sub_obj.y=4;
int a=sub_obj.Add_xy();
int s=sub_obj.Sub_xy();
System.out.println("x value is "+sub_obj.x);
System.out.println("y value is "+sub_obj.y);
System.out.println("sum is "+a);
System.out.println("subtraction is "+s);
}
}
Download Source>javac Inheritance.java
>java Inheritance
output:
x value is 10;
y value is 4;
sum is 14;
subtraction is 6;
Note : The object of the sub-class was created inside the main. The class Sub extends the class Add. This ist derives all the protected and public members of the class Add. The class Sub contains a method of it own, Sub_xy()/ The Object of class Sub in the main() is used to assign values to x and y and then the two methods are called.
Java does not support multiple inheritance directly. This means that the class in Java cannot have more than one super class.
Eg:
class Derived extends Super_one, Super_two
{
-----------------
-----------------
}
is illegal/not permitted in Java.
However, to be able to let the java programmers use the immense functionality provided by multiple inheritance, the java language developers incorporated this concept with the use of interfaces. (I will post an article about Interfaces with in few days)
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ItemReviewed: Java Inheritance Easy Lesson
