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Showing posts with label Internal Details of Hello Java Program. Show all posts
Showing posts with label Internal Details of Hello Java Program. Show all posts

Friday, January 23, 2015

Operators in java


Operators in java

Operator in java is a symbol that is used to perform operations. There are many types of operators in java such as unary operator, arithmetic operator, relational operator, shift operator, bitwise operator, ternary operator and assignment operator.

OperatorsPrecedence
postfixexpr++ expr--
unary++expr --expr +expr -expr ~ !
multiplicative* / %
additive+ -
shift<< >> >>>
relational< > <= >= instanceof
equality== !=
bitwise AND&
bitwise exclusive OR^
bitwise inclusive OR|
logical AND&&
logical OR||
ternary? :
assignment= += -= *= /= %= &= ^= |= <<= >>= >>>=

Useful Programs:

There is given some useful programs such as factorial number, prime number, fibonacci series etc.

It is better for the freshers to skip this topic and come to it after OOPs concepts.

1) Program of factorial number.

class Operation{  
  
 static int fact(int number){  
  int f=1;  
  for(int i=1;i<=number;i++){  
  f=f*i;  
  }  
 return f;  
 }  
  
 public static void main(String args[]){  
  int result=fact(5);  
  System.out.println("Factorial of 5="+result);  
 }  
}  

2) Program of fibonacci series.

class Fabnoci{  
   
  public static void main(String[] args)  
  {  
    int n=10,i,f0=1,f1=1,f2=0;  
    for(i=1;i<=n;i++)  
    {  
      f2=f0+f1;  
      f0=f1;  
      f1=f2;  
          f2=f0;  
          System.out.println(f2);  
    }  
      
   }  
 }  

3) Program of armstrong number.

class ArmStrong{  
  public static void main(String...args)  
  {  
    int n=153,c=0,a,d;  
    d=n;  
    while(n>0)  
    {  
    a=n%10;  
    n=n/10;  
    c=c+(a*a*a);  
    }  
    if(d==c)  
    System.out.println("armstrong number");   
    else  
    System.out.println("it is not an armstrong number");   
      
   }  
}  

4) Program of checking palindrome number.

class Palindrome  
{  
   public static void main( String...args)  
  {  
   int a=242;  
   int  n=a,b=a,rev=0;  
   while(n>0)  
   {  
     a=n%10;  
     rev=rev*10+a;  
     n=n/10;  
   }  
   if(rev==b)  
   System.out.println("it is Palindrome");  
   else  
   System.out.println("it is not palinedrome");  
    
  }  
}  

5) Program of swapping two numbers without using third variable.

class SwapTwoNumbers{  
public static void main(String args[]){  
int a=40,b=5;  
a=a*b;  
b=a/b;  
a=a/b;  
  
System.out.println("a= "+a);  
System.out.println("b= "+b);  
  
}  
}  

6) Program of factorial number by recursion

class FactRecursion{  
  
static int fact(int n){  
if(n==1)  
return 1;  
  
return n*=fact(n-1);  
}  
  
public static void main(String args[]){  
  
int f=fact(5);  
System.out.println(f);  
}  
}  

JVM (Java Virtual Machine)


JVM (Java Virtual Machine)

JVM (Java Virtual Machine) is an abstract machine. It is a specification that provides runtime environment in which java bytecode can be executed.
JVMs are available for many hardware and software platforms (i.e.JVM is plateform dependent).

What is JVM?

It is:
  1. A specification where working of Java Virtual Machine is specified. But implementation provider is independent to choose the algorithm. Its implementation has been provided by Sun and other companies.
  2. An implementation Its implementation is known as JRE (Java Runtime Environment).
  3. Runtime Instance Whenever you write java command on the command prompt to run the java class, and instance of JVM is created.

What it does?

The JVM performs following operation:
  • Loads code
  • Verifies code
  • Executes code
  • Provides runtime environment
JVM provides definitions for the:
  • Memory area
  • Class file format
  • Register set
  • Garbage-collected heap
  • Fatal error reporting etc.
Internal Architecture of JVM
Let's understand the internal architecture of JVM. It contains classloader, memory area, execution engine etc.

1) Classloader:

Classloader is a subsystem of JVM that is used to load class files.

2) Class(Method) Area:

Class(Method) Area stores per-class structures such as the runtime constant pool, field and method data, the code for methods.

3) Heap:

It is the runtime data area in which objects are allocated.

4) Stack:

Java Stack stores frames.It holds local variables and partial results, and plays a part in method invocation and return.
Each thread has a private JVM stack, created at the same time as thread.
A new frame is created each time a method is invoked. A frame is destroyed when its method invocation completes.

5) Program Counter Register:

PC (program counter) register. It contains the address of the Java virtual machine instruction currently being executed.

6) Native Method Stack:

It contains all the native methods used in the application.

7) Execution Engine:

It contains:
1) A virtual processor
2) Interpreter:Read bytecode stream then execute the instructions.
3) Just-In-Time(JIT) compiler:It is used to improve the performance.JIT compiles parts of the byte code that have similar functionality at the same time, and hence reduces the amount of time needed for compilation.Here the term ?compiler? refers to a translator from the instruction set of a Java virtual machine (JVM) to the instruction set of a specific CPU.

Difference between JDK, JRE and JVM


Difference between JDK, JRE and JVM

Understanding the difference between JDK, JRE and JVM is important in Java. We are having brief overview of JVM here.
If you want to get the detailed knowledge of Java Virtural Machine, move to the next page. Firstly, let's see the basic differences between the JDK, JRE and JVM.

JVM ( Java Virtual Machine )

JVM (Java Virtual Machine) is an abstract machine. It is a specification that provides runtime environment in which java bytecode can be executed.
JVMs are available for many hardware and software platforms. JVM, JRE and JDK are platform dependent because configuration of each OS differs. But, Java is platform independent.
The JVM performs following main tasks:
  • Loads code
  • Verifies code
  • Executes code
  • Provides runtime environment

JRE (Java Runtime Environment )


JRE is an acronym for Java Runtime Environment.It is used to provide runtime environment.It is the implementation of JVM.It physically exists.It contains set of libraries + other files that JVM uses at runtime.
Implementation of JVMs are also actively released by other companies besides Sun Micro Systems.



JDK (Java Development Tool kit )

JDK is an acronym for Java Development Kit.It physically exists.It contains JRE + development tools.

Thursday, January 22, 2015

Internal Details of Hello Java Program



In the previous page, we have learned about the first program, how to compile and how to run the first java program. Here, we are going to learn, what happens while compiling and running the java program. Moreover, we will see some question based on the first program.

What happens at compile time?
At compile time, java file is compiled by Java Compiler (It does not interact with OS) and converts the java code into bytecode.

What happens at runtime?

At runtime, following steps are performed:


Classloader: is the subsystem of JVM that is used to load class files.
Bytecode Verifier: checks the code fragments for illegal code that can violate access right to objects.
Interpreter: read bytecode stream then execute the instructions.

Q)Can you save a java source file by other name than the class name?

Yes, if the class is not public. It is explained in the figure given below:



To compile:javac Hard.java
To execute:java Simple

Q)Can you have multiple classes in a java source file?

Yes, like the figure given below illustrates: