Birla Soft Interview Question and Answers for Java 2- 4 year experience

The below questions asked by Birla Soft for Java/J2EE. I tried to give the best answer , hope it will help you out to crack the interview.

Q. Tell me about your self?

 Ans:  Give your brief introduction.

Q. Is Java Pass by Reference or Pass by Value?

Ans : Its always pass by value .

Q. What is the difference between an Interface and an Abstract class?

Ans : Both are looks similar. But, the basic difference is abstract class can contain abstract and non abstract methods, where interface only contains abstract method (without method body). You can declare fields that are not static and final, and define public, protected, and private concrete methods in abstract class. But, in Interface all members are public, static and final , all methods are public.

Q. What is the purpose of garbage collection in Java, and when is it used?

Ans : Garbage collection is a special feature in java language. It helps developer to save time and extra mental tension for handling object allocation in memory. It automatically clean the unused object from memory which helps to allocate space at runtime. When there is no reference to an object found, it will clean that object from memory . You can run the garbage collection explicitly by using System.gc() .

Q. What is Marker interface? How is it used in Java?

Ans : Marker interface is an interface which help us to notify few information to JVM/Compiler. The marker interface does not have any body, it’s a empty interface. Ex. Cloneable, Serialization, etc.            

Q. Can you give few examples of final classes defined in Java API?

Ans: String, Integer ,Float ,etc. Basically all wrapper classed are final.

Q. What is the importance of init() method in Servlet?

Ans:  init() method is one of the life cycle method of servlet. This method runs once in total life. After servlet instance created and before it handles request the init() method will work. Its basically used for initializing values at the time of application startup.

Q. How to improve Servlet Performance ?

Ans: You need to do few tuning for this achievement. Few points below :-

1.     Use init() method for all expensive operation during initialization (may be static data or cached data ).
2.     Always avoid auto loading of servlet.
3.     Avoid SingleThreadModel.
4.     Use and control HttpSession properly.

Q. How can a Servlet refresh automatically if some new data has entered the database?

Ans :  Basically it depends on the scenario , how you can handle. You need  handle this in DAO layer, when doing insert operation you can call an utility method which will load the context ServletContextListener. Because, servlets are basically used for handling request and give the response.

Q. How does JSP handle run-time exceptions?

Ans: You can use isErrorPage=”true” in page attribute.

Q. What is an EJB Context?

Ans: The EJBContext interface provides an instance with access to the container-provided runtime context of an enterprise bean instance.

Experienced Java/J2EE interview questions by MNC

Experienced Java/J2ee Interview questions asked by MNC.

1. Why main() in java is declared as public static void main? What if the main method is declared as
private?

Ans : Because, every program start execution from main function.The static method can directly call without creating the object of the class.So, before creating object the main function runs and then it creates object.

And, public in main method due to access by JVM. If the method is private then JVM cannot call that function.The program will compile but never run.It show the message  "Main method not public."


2.What is Externalization?

Ans : This interface is used for serialization.To save the state of an object in file. It provides two method
readExternal() and writeExternal().

3.What modifiers are allowed for methods in an Interface?
Ans : abstract and public

4.What are the different identifier states of a Thread?

Ans :
R- Running or Runnable
S- Suspended
MS- Thread Suspended on Monitor lock
MW- Thread waiting on monitor
CW- Thread waiting on condition variable


5.What are some alternatives to inheritance?

Ans : Delegation is an alternative to inheritance. Delegation means that you include an instance of another class as an instance variable, and forward messages to the instance. It is often safer than inheritance because it forces you to think about each message you forward, because the instance is of a known class, rather than a new class, and because it doesn’t force you to accept all the methods of the super class: you can provide only the methods that really make sense. On the other hand, it makes you write more code, and it is harder to re-use (because it is not a subclass).

6.Why isn’t there operator overloading?

Ans : Because C++ has proven by example that operator overloading makes code almost impossible to maintain.

7.What does it mean that a method or field is “static”?

Ans : Static method or field are member of class.They do not need any object for call or access . We can directly call the static method and fields without using the object.

Java Comparator Example for custom sorting by employee age and department

This program illustrates , how to sort custom object using Comparator<T>. We have used Employee list to sort by age and department. As per the default ordering it will follow the natural ordering.

The below Employee class is our POJO , we will use this class to sort the employee list by age and department.

Employee.java

package com.javadevelopersguide.lab.basic;
/**
 * @author manoj.bardhan
 *
 */
public class Employee {
private String name;
private int age;
private String department;
public Employee(String name, int age, String department) {
super();
this.name = name;
this.age = age;
this.department = department;
}
@Override
public String toString() {
return "\n Employee [name=" + name + ", age=" + age + ", department=" + department + "]";
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getDepartment() {
return department;
}
public void setDepartment(String department) {
this.department = department;
}
}

Now, we need to create a comparator to compare two same objects. We can create as many comparators by implementing each field/attributes of the POJO. Its purely business requirement, how you need your sorting functionality. Here we need the sorting based on the employee  age and employee department.

EmployeeAgeComparator.java

package com.javadevelopersguide.lab.basic;
import java.util.Comparator;
/**
 * EmployeeAgeComparator is a comparator by Age.
 *
 * @author manoj.bardhan
 *
 */
public class EmployeeAgeComparator implements Comparator<Employee> {
@Override
public int compare(Employee emp1, Employee emp2) {
return emp1.getAge() - emp2.getAge();
}
}

EmployeeDeptComparator.java

package com.javadevelopersguide.lab.basic;
import java.util.Comparator;
/**
 * EmployeeDeptComparator is comparator by department.
 *
 * @author manoj.bardhan
 *
 */
public class EmployeeDeptComparator implements Comparator<Employee> {
@Override
public int compare(Employee emp1, Employee emp2) {
// Internally for comparing String we need to use compareTo()
return emp1.getDepartment().compareTo(emp2.getDepartment());
}
}

In the above we created two comparator for age and department. Now, we need to action on our comparators. We will call our newly created comparator from main() and see the result. Below EmployeeComparatorExample class show the comparator in action.

EmployeeComparatorExample.java

package com.javadevelopersguide.lab.basic;
import java.util.ArrayList;
import java.util.Collections;
/**
 * This program illustrates the simple use of Comparator<t> interface.
 *
 * @author manoj.bardhan
 *
 */
public class EmployeeComparatorExample {
public static void main(String[] args) {
Employee e1 = new Employee("Matt Kuban", 32, "IT");
Employee e2 = new Employee("Andrew Smith", 42, "HR");
Employee e3 = new Employee("Butler Jason", 52, "HR");
Employee e4 = new Employee("Miss Linda", 35, "HR");
Employee e5 = new Employee("Bradley Head", 23, "IT");
Employee e6 = new Employee("Peter Parker", 34, "ADMIN");
// Create an arraylist and add all the employee object into that list.
ArrayList<Employee> employeeList = new ArrayList<Employee>();
employeeList.add(e1);
employeeList.add(e2);
employeeList.add(e3);
employeeList.add(e4);
employeeList.add(e5);
employeeList.add(e6);
System.out.println("Employee Before Sort ::" + employeeList);
// Using EmployeeAgeComparator - to sort the employee by Age
EmployeeAgeComparator ageComparator = new EmployeeAgeComparator();
Collections.sort(employeeList, ageComparator);
// Using EmployeeDeptComparator - to sort the employee by Department
EmployeeDeptComparator deptComparator = new EmployeeDeptComparator();
Collections.sort(employeeList, deptComparator);
System.out.println("Employee After Sort ::" + employeeList);
}
}

Output :- 

Employee Before Sort ::[
 Employee [name=Matt Kuban, age=32, department=IT],
 Employee [name=Andrew Smith, age=42, department=HR],
 Employee [name=Butler Jason, age=52, department=HR],
 Employee [name=Miss Linda, age=35, department=HR],
 Employee [name=Bradley Head, age=23, department=IT],
 Employee [name=Peter Parker, age=34, department=ADMIN]]

Employee After Sort ::[
 Employee [name=Peter Parker, age=34, department=ADMIN],
 Employee [name=Miss Linda, age=35, department=HR],
 Employee [name=Andrew Smith, age=42, department=HR],
 Employee [name=Butler Jason, age=52, department=HR],
 Employee [name=Bradley Head, age=23, department=IT],
 Employee [name=Matt Kuban, age=32, department=IT]]

Happy Learning.

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