Java Language fundamentals

Language Fundamentals

How many number of non-public class definitions can a source file have

A source file can contain unlimited number of non-public class definitions

 

List primitive data types, there size and there range (min, max)

 

Data Type	Bytes	bits	min	max
boolean	-	1	-	-
char	2	16	0	2^16-1
byte	1	8	-2^7	2^7-1
short	2	16	-2^15	2^15-1
int	4	32	-2^31	2^31-1
long	8	64	-2^63	2^63-1
float	4	32	-	-
double	8	64	-	-

 

What types of values does boolean variables take

It only takes values true and false

Which primitive datatypes are signed

All except char and Boolean

Is char type signed or unsigned

char type is integral but unsigned. It range is 0 to 2^7-1

What forms an integral literal can be

decimal, octal and hexadecimal, hence example it can be 28, 034 and 0x1c respectively

What is the default value of boolean

False

Why is the main method static

So that it can be invoked without creating an instance of that class

What is the difference between class variable, member variable and automatic(local) variable

class variable is a static variable and does not belong to instance of class but rather shared across all the instances
member variable belongs to a particular instance of class and can be called from any method of the class
automatic or local variable is created on entry to a method and has only method scope

When are static and non static variables of the class initialized

The static variables are initialized when the class is loadedNon static variables are initialized just before the constructor is called

When are automatic variable initialized

Automatic variable have to be initialized explicitly

How is an argument passed in java, by copy or by reference

If the variable is primitive datatype then it is passed by copy.
If the variable is an object then it is passed by reference

What is garbage collection

The runtime system keeps track of the memory that is allocated and is able to determine whether that memory is still useable. This work is usually done in background by a low-priority thread that is referred to as garbage collector. When the gc finds memory that is no longer accessible from any live thread it takes steps to release it back to the heap for reuse

Does System.gc and Runtime.gc() guarantee garbage collection

No