Question { TCS, 90802 }

Difference between JDK, JRE, JVM

Answer

JDK :-it means that we r developing applications,after
developing we r compiling a program through javac.Here the
javac is in jdk part.after compiling it makes a .class
file(nothing but a bytecode),bytecode contains assembly
language,here byte is 8 bits so it's cpacity is 255,here 255
is contains opcodes(operation codes) values.That is jvm is
not a part of jdk.

JRE :-it means excecution(running) a program.here we r
having jvm in jre.first of all bytecode is loaded on jvm
that is nothing but a assembly language will be converted
into java virtual machine language

JVM :-it is the form ofjava virtual machine language of
bytecode,now the jvm language will provide the message of
output in user understandable language(high level lang).

Question { IBM, 176567 }

explain System.out.println

Answer

System is a built-in class present in java.lang package.
This class has a final modifier, which means that it cannot
be inherited by other classes.
It contains pre-defined methods and fields, which provides
facilities like standard input, output, etc.

out is a static final field (ie, variable)in System class
which is of the type PrintStream (a built-in class,
contains methods to print the different data values).
static fields and methods must be accessed by using the
class name, so ( System.out ).

out here denotes the reference variable of the type
PrintStream class.

println() is a public method in PrintStream class to print
the data values.
Hence to access a method in PrintStream class, we use
out.println() (as non static methods and fields can only be
accessed by using the refrence varialble)