Question 1

What are pass by reference and passby value ?

Accepted Answer

Pass By Reference means the passing the address itself rather than passing the value Passby Value means passing a copy of the value to be passed

Question 2

Difference between Swing and Awt ?

Accepted Answer

AWT are heavy-weight componenets Swings are light-weight components Hence swing works faster than AWT

Question 3

What is synchronization and why is it important ?

Accepted Answer

With respect to multithreading, synchronization is the capability to control the access of multiple threads to shared resources Without synchronization, it is possible for one thread to modify a shared object while another thread is in the process of using or updating that object's value This often leads to significant errors

Question 4

What are wrapped classes ?

Accepted Answer

Wrapped classes are classes that allow primitive types to be accessed as objects

Question 5

What is the purpose of the wait(), notify(), and notifyAll() methods ?

Accepted Answer

The wait(), notify(), and notifyAll() methods are used to provide an efficient way for threads to wait for a shared resource When a thread executes an object's wait() method, it enters the waiting state It only enters the ready state after another thread invokes the object's notify() or notifyAll() methods

Question 6

What is top level class?

Accepted Answer

Top level class is also called outer class It is not defined inside any class Ex: class A { //top level class }

Question 7

What is static member class?

Accepted Answer

Static member class is a class defined inside outer class with static modifier EX: Class A { //top level class or outer class static class B { //static member class } }

Question 8

what is non-static member class?

Accepted Answer

Non-static member class is a class defined inside outer class with out static modifier EX: class A { // top level class or outer class class B { //non-static member class } }

Question 9

What is local class?

Accepted Answer

Local class is class defined inside method EX; class A { // top level class public static void main(string[] args) { class B { // local class } } }

Question 10

What is anonymous class?

Accepted Answer

Anonymous class is class without name EX: class A { } class Demo { A r = new A() { }; //anonymous class }

Question 11

What is the syntax to create the object?

Accepted Answer

new ClassName(); This expression creates object in heap area and returns that obj address Here JVM creates object but JVM does not returns object original address JVM returns duplicate address, duplicate address is also called as hashcode

Question 12

How to assign address to the reference?

Accepted Answer

ClassName refName = new ClassName(); or ClassName refName; refName = new ClassName();

Question 13

Why static method can not call non static method of the same class?

Accepted Answer

bcoz the static method does not contains the 'this' reference

Question 14

What is stored in the 'this' reference?

Accepted Answer

This is a keyword and used as reference to Current object address in java It means by using which object the method is called that object hashcode is stored inside the 'this'

Question 15

When this. non-static datamember is compulsory inside non-static method

Accepted Answer

Whenever there is local- variable/parameter inside the method with same name as data member Ex: Class Sample { int a; void show() { int a=5; systemoutprintln(a); // 5 systemoutprintln(thisa);//23 } } class MainApp { Public static void main(String[] args) { Sample s = new Sample(); sa = 23; sshow(); } }

Question 16

What is the differnce among public, protected and package access data?

Accepted Answer

If we are not using packages and if we are not using inheritance then there is no difference among public, protected and package access data

Question 17

In a class if private data member is declared then how to set data to that private data member?

Accepted Answer

By using method The method used to set the data is called setter method

Question 18

In a class if private data member is declared then how to get value of that data member?

Accepted Answer

By using method The method used to get the data is called getter method

Question 19

What is difference between methods and blocks?

Accepted Answer

Method contains name, parameters, return type and executable body But block does not contains name, parameters, return typeIt contains only executable body Methods are executed by method call statements Blocks are executed automatically with class loading and with object creation

Question 20

What is Constructor?

Accepted Answer

Constructor is not a special method Constructor is block of code that is executed automatically whenever object of the class is created

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