1.what is difference between #include and import statement
Ans:#include makes the compiler to go the c/c++ library and
copy the code in our program from header file. So program size will be
increased and to compile that code waste of time. And memory will be wasted
Import statement makes the jvm to go the java standard
library, execute the code there and it brings back only the results into our
program. Here no code is copied and hence no waste of memory.
So import is an more efficient than #include
2. what is difference between print() and println() in java
3. Can we call main() method from anther class
Ans: yes we can call.
Ex:class a
{
Public static void main(String arg[])
{
System.out.println(“hai..”);
}
}
}
Class b
{
Public static void main(String arg[])
{
a.main(arg);
}
}
4.What is Jagged Arrays in java
Ans: a jagged array is an array that contains a group of
arrays within it. A jagged array can store arrays of any size. Jagged arrays
are also called “irregular multidimensional arrays”
Ex:int x[][]=new int[2][];
X[0]=new int[3];
//memory for first array.
X[1]=new int[2];//memory for 2nd array.
X[0]--->x[0][0],x[0][1],x[0][2]
X[1]--->x[1][0],x[1][1],x[1][2]
Program
class class3
{
public static void main(String
arg[])
{
int x[][]=new int[2][];
x[0]=new int[3];
x[1]=new int[2];
//assign
values for first array
int s=10;
for(int i=0;i<3;i++)
{
x[0][i]=s;
s=s+10;
}
//assign
values for second array
s=100;
for(int i=0;i<2;i++)
{
x[1][i]=s;
s=s+100;
}
//display
first array
for(int i=0;i<3;i++)
{
System.out.println(x[0][i]);
}
//similarly
display second array also
}
}
5.What if the main
method is declared as private?
The program compiles properly but at
runtime it will give "Main method not public." message.
6.Expain the reason for each keyword of
public static void main(String args[])?
public- main(..) is the
first method called by java environment when a program is executed so it has to
accessible from java environment. Hence the access specifier has to be public.
static: Java environment
should be able to call this method without creating an instance of the class ,
so this method must be declared as static.
void: main does not
return anything so the return type must be void
The argument String indicates the
argument type which is given at the command line and arg is an array for string
given during command line.
7.What are the differences between == and .equals() ?
The == operator compares two objects to
determine if they are the same object in memory i.e. present in the same memory
location. It is possible for two String objects to have the same value, but
located in different areas of memory.
== compares references while .equals
compares contents. The method public boolean equals(Object obj) is provided by
the Object class and can be overridden. The default implementation returns true
only if the object is compared with itself, which is equivalent to the equality
operator == being used to compare aliases to the object. String, BitSet, Date,
and File override the equals() method. For two String objects, value equality
means that they contain the same character sequence. For the Wrapper classes,
value equality means that the primitive values are equal.
|
public class
EqualsTest {
public static void main(String[] args) {
String s1 = "abc";
String s2 = s1;
String s5 = "abc";
String s3 = new
String("abc");
String s4 = new
String("abc");
System.out.println("==
comparison : " + (s1 == s5));
System.out.println("==
comparison : " + (s1 == s2));
System.out.println("Using
equals method : " + s1.equals(s2));
System.out.println("==
comparison : " + s3 == s4);
System.out.println("Using
equals method : " + s3.equals(s4));
}
}
|
8.What is final, finalize() and finally?
o final - declare
constant
o finally - handles exception
o finalize - helps in garbage collection
Variables defined in an interface are implicitly final. A final class
can't be extended i.e., final class may not be subclassed. This is done for
security reasons with basic classes like String and Integer. It also allows the
compiler to make some optimizations, and makes thread safety a little easier to
achieve. A final method can't be overridden when its class is inherited. You
can't change value of a final variable (is a constant). finalize() method is
used just before an object is destroyed and garbage collected. finally, a key
word used in exception handling and will be executed whether or not an exception
is thrown. For example, closing of open connections is done in the finally
method.o finally - handles exception
o finalize - helps in garbage collection
9.What is the GregorianCalendar class?
The GregorianCalendar provides support
for traditional Western calendars.
GregorianCalendar is a concrete subclass of Calendar and provides the standard calendar system used by most of the world.
10.Why there are no global variables in
Java?
Global variables are
globally accessible. Java does not support globally accessible variables due to
following reasons: The global variables breaks the referential transparency
Global variables creates collisions in namespace
11.What is the SimpleTimeZone class?
The SimpleTimeZone class provides support for a Gregorian calendar
12.How does Java handle integer overflows
and underflows?
It uses those low order bytes of the
result that can fit into the size of the type allowed by the operation.
No comments:
Post a Comment