Friday, July 25, 2008
What is the difference between interpreted code and compiled code?
An interpreter produces a result from a program, while a compiler produces a program written in assembly language and in case of Java from bytecodes.The scripting languages like JavaScript,Python etc. require Interpreter to execute them.So a program written in scripting language will directly be executed with interpreter installed on that computer,if it is absent then this program will not execute.While in case of compiled code,an assembler or a virtual machine in case of Java is required to convert assembly level code or bytecodes into machine level instructions/commands.Generally, interpreted programs are slower than compiled programs, but are easier to debug and revise.
What is Java class file's magic number?
A Magic Number of a class file is a unique identifier for tools to quickly differentiate class files from non class files.The first four bytes of each Java class file has the magic value as 0xCAFEBABE.And the answer to why this number,I do not actually know but there may be very few sensible and acceptable options possible constructed from letters A-F which can surely not be 'CAFEFACE' or 'FADECAFE'....
What is heap and stack?
The heap is the part of memory of JVM where all objects reside.
The stack is consisted of stack frames.When a thread invokes a method,the JVM pushes a new frame onto that thread's Java stack.Each stack frame is consisted of operand stack and the local variable array.All arguments,local variables,intermediate computations and return values if any are kept in these stack corresponding to the method invoked.The stack frame on the top of the stack is called the active stack frame,which is the current place of execution.When the method completes, the virtual machine pops and discards the frame for that method.
The stack is consisted of stack frames.When a thread invokes a method,the JVM pushes a new frame onto that thread's Java stack.Each stack frame is consisted of operand stack and the local variable array.All arguments,local variables,intermediate computations and return values if any are kept in these stack corresponding to the method invoked.The stack frame on the top of the stack is called the active stack frame,which is the current place of execution.When the method completes, the virtual machine pops and discards the frame for that method.
How is Java different from C++?
Java is a platform independent, object oriented language while C++ is having some of its features from C, which is a procedural language so it is not pure object oriented. Even java is not 100% object oriented.
1. Pointers are supported in C++ while not in Java. The memory management is done automatically with help of part of JVM called Garbage Collector.
2. Multiple inheritance is not supported in Java but supported in C++.
3. There are no structures, unions or enumeration in Java.
4. There is no scope resolution operator in Java (::).
5. There are no destructors in Java like C++.
6. There is no virtual keyword in Java because all non-static method use dynamic binding.
1. Pointers are supported in C++ while not in Java. The memory management is done automatically with help of part of JVM called Garbage Collector.
2. Multiple inheritance is not supported in Java but supported in C++.
3. There are no structures, unions or enumeration in Java.
4. There is no scope resolution operator in Java (::).
5. There are no destructors in Java like C++.
6. There is no virtual keyword in Java because all non-static method use dynamic binding.
What is method overriding?
The method with same signature but with changed implementation lead to method overriding and that can occur in a parent child relation of classes. A method defined in parent class can be overridden in its child class with different implementation from its base class.
An example:
We will define a base class called Circle
class Circle
{
//declaring the instance variableprotected double radius;
public Circle(double radius)
{
this.radius = radius;
}
// other method definitions here
public double getArea()
{
return Math.PI*radius*radius;
}
//this method returns the area of the circle
}// end of class circle
When the getArea method is invoked from an instance of the Circle class, the method returns the area of the circle.
The next step is to define a subclass to override the getArea() method in the Circle class. The derived class will be the Cylinder class. The getArea() method in the Circle class computes the area of a circle, while the getArea method in the Cylinder class computes the surface area of a cylinder.
The Cylinder class is defined below.
class Cylinder extends Circle
{
//declaring the instance variableprotected double length;
public Cylinder(double radius, double length)
{
super(radius);this.length = length;
}
// other method definitions herepublic
double getArea()
{
// method overriden here
return 2*super.getArea()+2*Math.PI*radius*length;
}//this method returns the cylinder surface area
}// end of class Cylinder
When the overriden method (getArea) is invoked for an object of the Cylinder class, the new definition of the method is called and not the old definition from the superclass(Circle).
An example:
We will define a base class called Circle
class Circle
{
//declaring the instance variableprotected double radius;
public Circle(double radius)
{
this.radius = radius;
}
// other method definitions here
public double getArea()
{
return Math.PI*radius*radius;
}
//this method returns the area of the circle
}// end of class circle
When the getArea method is invoked from an instance of the Circle class, the method returns the area of the circle.
The next step is to define a subclass to override the getArea() method in the Circle class. The derived class will be the Cylinder class. The getArea() method in the Circle class computes the area of a circle, while the getArea method in the Cylinder class computes the surface area of a cylinder.
The Cylinder class is defined below.
class Cylinder extends Circle
{
//declaring the instance variableprotected double length;
public Cylinder(double radius, double length)
{
super(radius);this.length = length;
}
// other method definitions herepublic
double getArea()
{
// method overriden here
return 2*super.getArea()+2*Math.PI*radius*length;
}//this method returns the cylinder surface area
}// end of class Cylinder
When the overriden method (getArea) is invoked for an object of the Cylinder class, the new definition of the method is called and not the old definition from the superclass(Circle).
What is method overloading?
A method with changed formal parameters will lead to implementing method overloading.
int calculateSum(int i,int j)
float calculateSum(float i,int j)
double calculateSum(double i,int j)
float calculateSum(int i,float j)
int calculateSum(int i,int j)
float calculateSum(float i,int j)
double calculateSum(double i,int j)
float calculateSum(int i,float j)
Why is Java not 100% pure OOP language?
Java takes inspirations from C and C++.The native datatypes like 'char','int','float','double' are straight pick from C, which is not an Object Oriented Language.Resonably enough, Java is not a 100% pure Object Oriented Language.
Subscribe to:
Posts (Atom)
