INTERVIEW QUESTIONS J2EE CORE JAVA DETAILS

Question: Explain the different forms of Polymorphism.

Answer: Polymorphism exists in three distinct forms in Java:

1.Method overloading
2. Method overriding through inheritance
3. Method overriding through the Java interface

Polymorphism exists in three distinct forms in Java:

1.Method overloading
2. Method overriding through inheritance
3. Method overriding through the Java interface
Source: CoolInterview.com

polymorphism is of two type-
1. compile time (method overloading)
2.run time(method overriding)
Source: CoolInterview.com

The Greek Work "Poly" means many and "Morph" means forms. The Polymorphism has many types that depend on the situation in which we are use the concept on polymorphism. Like:
if we add to Number 10+20 then result will be 30, but when we use the + operator with string like "Harry"+" Potter" then the ouput will be Harry Potter. So according to the situation it plays the many role. Source: CoolInterview.com

Actually both method overloading and overriding are examples of runtime polymorphism.

Because in overloading you never know what parameter you are passing at run time, based on the type of parameter it(jvm) will decide what method it should call.

Other than these two types are compile time polymorphism, like simple or plain method calling. Source: CoolInterview.com

polymorphism translates from Greek as many forms ( poly - many morph - forms)
in OOP's it refers to
the propensity of objects to react differently to the same method (VA pg 110)
method overloading is the primary way polymorphism is implemented in Java
Overloading methods
overloaded methods:
appear in the same class or a subclass
have the same name but,
have different parameter lists, and,
can have different return types
an example of an overloaded method is print() in the java.io.PrintStream class
public void print(boolean b)
public void print(char c)
public void print(char[] s)
public void print(float f)
public void print(double d)
public void print(int i)
public void print(long l)
public void print(Object obj)
public void print(String s)
the actual method called depends on the object being passed to the method
Java uses late-binding to support polymorphism; which means the decision as to which of the many methods should be used is deferred until runtime
Overriding methods
late-binding also supports overriding
overriding allows a subclass to re-define a method it inherits from it's superclass
overriding methods:
appear in subclasses
have the same name as a superclass method
have the same parameter list as a superclass method
have the same return type as as a superclass method
the access modifier for the overriding method may not be more restrictive than the access modifier of the superclass method
if the superclass method is public, the overriding method must be public
if the superclass method is protected, the overriding method may be protected or public
if the superclass method is package, the overriding method may be packagage, protected, or public
if the superclass methods is private, it is not inherited and overriding is not an issue
the throws clause of the overriding method may only include exceptions that can be thrown by the superclass method, including it's subclasses
class LBException extends Exception {}
class LBException1 extends LBException {}

In superclass:
public void testEx() throws LBException {
throw new LBException();
}

In subclass:

public void testEx() throws LBException1 {
throw new LBException1();
}
overriding is allowed as LBException1 thrown in the subclass is itself a subclass of the exception LBException thrown in the superclass method Source: CoolInterview.com

Universal polymorphism:
1. Inclusion polymorphism
o It refers to the ability of an object to invoke a method that it inherits.
2. Parametric Polymorphism
o This kind of polymorphism occurs with generic methods, where an actual type is substituted in for a type parameter.
Ad hoc polymorphism:
1. Overloading
2. Coercion
Coercion occurs when a value of one type is implicitly converted to a value of another type when the context requires that other type. For example, when the compiler evaluates the expression
22 + 3.3, it interprets the plus operator as floating point addition, requiring both operands to be either type float or type double. So it “coerces” the 22 into being 22.0 and then performs the operation.
Source: CoolInterview.com

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