Question 1

How to call argument constructor?

Accepted Answer

new ClassName( arg1, arg2, argN); Ex: Class sample { Sample(int a) { Systemoutprintln("arg con a =" +a); } } class Demo { Public static void main( String[] args) { Sample s1= new Sample(23); Sample s2= new Sample(45); } }

Question 2

What is different among String, StringBuffer, StringBuilder?

Accepted Answer

String class objects are immutable objects and they represents strings( sequence of characters) StringBuffer class objects are mutable objects representing strings and they are Thread safe StringBuild class objects are also mutable objects representing strings and they are not Thread safe

Question 3

What is wrapping?

Accepted Answer

Wrapping is also called as packing or boxing Storing the data inside the object as private data which can accessed outside the class only by using methods

Question 4

What is unwrapping?

Accepted Answer

Unwrapping is also called as unpacking or unboxing Getting the private data stored in the object by using methods is called unpacking or unwrapping

Question 5

What is JAR file? what are the main uses of JAR files?

Accepted Answer

JAR files are java's version of ZIP files In fact, JAR uses the ZIP file format uses: - to compress a number of class files into one file - to make a java executable JAR file

Question 6

What is the difference between path and classpath?

Accepted Answer

Path contains path of exe files(commands) Classpath contains path of packages packages can be stored in folder or jar files

Question 7

What is the use of super call?

Accepted Answer

By using super call we can call super class constructors from sub class constructors and we can initialize super class private data

Question 8

If super class ref is pointing sub class object then by using super class ref is it possible to call sub class newly defined method?

Accepted Answer

yes if the method is ovreriding method no if the method is not overriding method

Question 9

What is the use of overriding?

Accepted Answer

- By using method overriding a sub class can change the definition of super class method - By using overriding a sub class can modify the functionality of the super class

Question 10

What is the use of overloading ? or why overloading?

Accepted Answer

By using overloading we can add new functionality to the sub class

Question 11

What is final method?

Accepted Answer

Final method is a method defined in the super class with final modifier We cannot overriding final method of super class in the sub class EX: Class Sample { final void funOne() { } void funTwo() { } } Class Sub extends Sample { void funOne() { // overriding is not allowed } viod funTwo() { //overriding is allowed } }

Question 12

What is the purpose of overriding toString() method?

Accepted Answer

we can override tostring() method to return String representation of our object data

Question 13

why overriding finalize() method?

Accepted Answer

If constructor opens the file finalize() method closes that file If constructor opens the connection finalize() method closes that connection To perform finalization operation we must overriding finalize method

Question 14

What is the use of tostring() method?

Accepted Answer

If we print any object by using println() or print() methods The println() or print() methods internally calls tostring() method and prints the return value of toString() method

Question 15

why protected modifier?

Accepted Answer

Outside the package if any other class other than JVM calls the finalize method our class then it is not allowed

Question 16

What is abstract method?

Accepted Answer

abstract method is a method declared with abstract modifier but with out body

Question 17

Why interface data is static?

Accepted Answer

Interface data is static data why bcoz interface supports multiple inheritance if inteface data is non-static then there is chance for replication of the data (bcoz of replication of data ambiguity problem occurs )

Question 18

Why interface data is final?

Accepted Answer

bcoz interface does not contains any initializers and constructors to initialize its data members

Question 19

Why interface data is public?

Accepted Answer

to access non-public data outside class getter methods be defined but we cannot define a method inside interface we can declared a method inside interface

Question 20

How to create a file on the hard disk by using File class object?

Accepted Answer

We can use the following method call: boolean createNewFile(); This method creates a new file on the HD If a file is already existing with the name given in the constructor then this method does not creates file on HD If file is successfully created then this method returns true If file is already existing on the HD then this method returns false This method may throw IOException whenever IO error is generated while creating file on HD

Technology Questions