Why in java interface is used for multiple inheritance not by extends?

Answer 1

Since an interface has no implemented methods, there is nothing to extend, since you would simply get empty method headings you can't make a class by extending an interface. An interface must be implemented, by filling in the method bodies. An interface is a tool to define common characteristics between classes, i.e. how they act. For instance, an interface might be used to define a window, a simple generic window: it opens, closes, breaks.

Interfaces are useful to the client since you don't need to know the inner workings of the class to use it, for instance, as long as you know the data structure you are working with is a List, you don't need to know whether it is an ArrayList or LinkedList.

Answer 2

Hi All,

In this question there is a very good trick had been used by James gosling. Actually java doesn't supports multiple inheritance. Only interface can be used to do so. it is because java supports inheritance. Java also supports classes within classes. So in Interface that classes within classes mechanism is there. This mechanism is behind the keyword Interface . The keyword Interface means it is classes within classes. so By implicitly we are using multiple inheritance by the use of interface..

Pranab Kumar Rana

Software Engineer...

Code

Simple Program On Java for the implementation of Multiple inheritance using interfaces to calculate the area of a rectangle and triangle

/* Area Of Rectangle and Triangle using Interface * /

interface Area

{

float compute(float x, float y);

}

class Rectangle implements Area

{

public float compute(float x, float y)

{

return(x * y);

}

}

class Triangle implements Area

{

public float compute(float x,float y)

{

return(x * y/2);

}

}

class InterfaceArea

{

public static void main(String args[])

{

Rectangle rect = new Rectangle();

Triangle tri = new Triangle();

Area area;

area = rect;

System.out.println("Area Of Rectangle = "+ area.compute(1,2));

area = tri;

System.out.println("Area Of Triangle = "+ area.compute(10,2));

}

}

/** OUTPUT **

Area Of Rectangle = 2.0

Area Of Triangle = 10.0

• /

Niraj Sharma