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What is the alternate of 'Inheritance' ?
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Answer / manish
Association(make the object of that any particular class and
use it's properties and behaviours(data member and member
function)).
| Is This Answer Correct ? | 31 Yes | 1 No |
Answer / rakesh sahoo
Inheritance in JAVA programming is the process by which one class takes the property of another other class. i.e. the new classes, known as derived or super class, take over the attributes and behavior of the pre-existing classes, which are referred to as base classes or child class.
Inheritance is used to create a hierarchical-type code structure that tries to keep as much “common” code near the top of the hierarchy. In small, static systems, inheritance can be ok. But large inheritance chains can also lead to hard-to-maintain code. Read up on design patterns that favor composition over inheritance for more info when to use inheritance and when not to.
Delegation is simply passing a duty off to someone/something else.Delegation is alternative to inheritance. Delegation means that you use an object of another class as an instance variable, and forward messages to the instance. It is better than inheritance because it makes you to think about each message you forward, because the instance is of a known class, rather than a new class, and because it doesn’t force you to accept all the methods of the super class: you can provide only the methods that really make sense.Delegation can be viewed as a relationship between objects where one object forwards certain method calls to another object, called its delegate. Delegation can also a powerful design/reuse technique. The primary advantage of delegation is run-time flexibility – the delegate can easily be changed at run-time. But unlike inheritance, delegation is not directly supported by most popular object-oriented languages, and it doesn’t facilitate dynamic polymorphism.
Here is a simple example:
class ABC {
void methodHello()
{
System.out.println("hello");
}
void methodBye()
{
System.out.println("bye"); }
}
class XYZ {
ABC obj = new ABC();
void methodHello()
{
obj.methodHello();
}
void methodBye()
{
obj.methodBye();
}
}
public class VinayMain {
public static void main(String[] args) {
XYZ obj = new XYZ();
obj.methodHello();
obj.methodBye();
}
}
Sometimes, the choice between delegation and inheritance is driven by external factors such as programming language support for multiple inheritance or design constraints requiring polymorphism. Consider threads in Java. You can associate a class with a thread in one of two ways: either by extending (inheriting) directly from class Thread, or by implementing the Runnable interface and then delegating to a Thread object. Often the approach taken is based on the restriction in Java that a class can only extend one class (i.e., Java does not support multiple inheritance). If the class you want to associate with a thread already extends some other class in the design, then you would have to use delegation; otherwise, extending class Thread would usually be the simpler approach
| Is This Answer Correct ? | 1 Yes | 0 No |
Answer / nikshay
delegation(it is usefull becoz u know about message u pass that associate with ur objects, so yes delegation.
| Is This Answer Correct ? | 2 Yes | 2 No |
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3.2 Consider the following class: public class Point { protected int x, y; public Point(int xx, int yy) { x = xx; y = yy; } public Point() { this(0, 0); } public int getx() { return x; } public int gety() { return y; } public String toString() { return "("+x+", "+y+")"; } } Say you wanted to define a rectangle class that stored its top left corner and its height and width as fields. 3.2.1 Why would it be wrong to make Rectangle inherit from Point (where in fact it would inherit the x and y coordinates for its top left corner and you could just add the height and width as additional fields)? (1) 8 Now consider the following skeleton of the Rectangle class: public class Rectangle { private Point topLeft; private int height, width; public Rectangle(Point tl, int h, int w) { topLeft = tl; height = h; width = w; } public Rectangle() { this(new Point(), 0, 0); } // methods come here } 3.2.2 Explain the no-argument constructor of the Rectangle class given above. 3.2.3 Write methods for the Rectangle class to do the following: • a toString() method that returns a string of the format "top left = (x, y); height = h; width = w " where x, y, h and w are the appropriate integer values. • an above() method that tests whether one rectangle is completely above another (i.e. all y values of the one rectangle are greater than all y values of the other). For example, with the following declarations Rectangle r1 = new Rectangle(); Rectangle r2 = new Rectangle(new Point(2,2), 1, 4); the expression r2.above(r1) should give true, and r2.above (r2) should give false. (You can assume that the height of a rectangle is never negative.) (2) (5)
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