Part 1
Basic Java Interview Questions and Answers covered in this post:
What is object-oriented language? Is
java 100% object-oriented language? Why?
- Object-oriented programming is about creating an object which
can have its data and methods.
- Java supports primitive data types like int, float, double
etc. which is not an object, so Java is not a purely object-oriented
language.
What is platform-independent? Why java
is platform-independent?
- Platform independent means “write once run anywhere”. In
short, once you write a program on any platform can run it on any
platform. e.g. If you wrote a program on Unix can run it on windows or
any other platform or operating system.
Once the Java program compiles that program converts into byte code. Byte
code is not platform dependent so Java is platform-independent.
 
Note: Please click on Image to Purchase the books from Amazon.in |
What is a Class?
- Class is a blueprint or template, from object can be
created.
- E.g. I have a class with the name Person. I have created '10'
objects of the Person class. Each object has its copy of each member
variable.
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package simplifiedjava.crackedInterview;
public class Person {
private int age;
private int height;
private int weight;
private String name;
private String education;
// Getter and setter methods.
}
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What is an Object?
- Generally, an Object is a real-time entity. Objects are the
behaviour of the class.
- Technically an Object is the combination of data and
functions.
What is JVM? What is the difference
between JDK, JVM and JRE?
- JVM stands for Java Virtual Machine.
- JVM provides a runtime environment in which byte code can be executed.
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JDK |
JVM |
JRE |
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JDK Stands for Java Development Kit. |
JVM Stands for Java Virtual Machine. |
JRE Stands for Java Runtime Environment. |
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JDK Physically exist in System |
JVM exist virtually but not physically. |
JRE exists physically. |
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JDK = JRE + JVM |
JVM is a run time environment in which bytecode can execute. |
JRE is an Implementation of JVM. |
What is the class loader and what are
the types of class loaders?
- ClassLoader loads the classes dynamically into memory
whenever required by Java Runtime Environment.
- ClassLoader is an abstract class in Java Runtime
Environment.
- There are three types of class loaders available in java.
a. BootStrap Class Loader (Primordial ClassLoader):
This is a parent loader of all existing loaders. Bootstrap loaders load all
JDK files from jre/lib/rt.jar.
b. Extension Class Loader :
Extension class loader loads the extensions of java core classes from
jre/lib/ext directory. Extension class loader is a child loader of Bootstrap
class loader.
c. System Class Loader :
System class loader loads the application level classes. System class
loader is a child loader of Extension class loader.
What is Heap memory and Stack Memory?
What is the difference between Heap Memory Stack Memory?
- Heap Memory :
o Heap memory is used to store the Objects.
- Stack Memory:
o Stack memory is used to store the local variables and
function list.
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Heap Memory |
Stack Memory |
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1. |
Heap memory stores the objects. |
Stack Memory stores local variables, reference variables and
methods. |
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2. |
Objects stores in a hierarchical manner. |
Variables stores in a sequential manner. |
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3. |
Objects can reside in heap memory until it points to reference
variable. |
Variables will be removed once the function is executed. |
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4. |
Access speed is slow. |
Access speed is high. |
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5. |
If Heap memory gets full JVM immediately throw
OutOfMemoryError. |
If Stack gets full JVM immediately throws StackOverflowError. |
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6. |
The Garbage collections mechanism is used to reclaim the
memory. |
There is no role of garbage collector because variables are
automatically removed once the function is executed. |
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7. |
Heap is a flexible memory. |
Stack is not flexible memory. |
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8. |
-Xms and –Xmx JVM options can be used to increase or decrease the
size of the Heap. |
-Xss option can be used to increase the size of the stack. |
Explain the Term Association,
Composition, and Aggregation? What is HAS-A and IS-A Relationship?
- Association: Creating the relationship between two
objects is referred to as Association.
Ø Association can be One-to-One, One-to-Many, Many-to-One,
Many-to-Many.
Ø Aggregation and Composition are two forms of Association.
Ø One-to-One = One Student can have one Class.
Ø One-to-Many = One Student can have multiple Subjects.
Ø Many-to-One = Many developers can have one Project
Manager.
Ø Many-to-Many = Multiple Employees can have Multiple
Tasks.
Ø Example of Association. We have created an association
between Company and Employees.
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package simplifiedjava.crackedInterview;
public class Company {
private String companyName;
public Company(String companyName) {
this.companyName = companyName;
}
public String getCompanyName() {
return companyName;
}
}
package simplifiedjava.crackedInterview;
public class Employee {
private String empName;
public Employee(String empName) {
this.empName = empName;
}
public String getEmpName() {
return empName;
}
}
package simplifiedjava.crackedInterview;
public class AssociationExample {
public static void main(String[] args) {
Employee employee1 = new Employee("Rusty");
Company company = new Company("Company");
System.out.println(employee1.getEmpName() + " is working for "+ company.getCompanyName());
}
}
OUTPUT : Rusty is working for Company. |
- Composition:
ü The composition can be called the HAS-A relationship.
ü When two objects are tightly coupled with each other or we
can say when one object is dependent on another object is called
Composition.
ü E.g. Engine cannot survive without a car. If a car
exists then an engine exists. If a car is destroyed automatically engine
gets destroyed.
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package simplifiedjava.crackedInterview; public class Engine {
private String engineName;
private String power; private String modelNo;
// getter and Setter methods. } package simplifiedjava.crackedInterview; public class Car {
private String carName;
private String carModel; private String manufacturer; private Engine engine; // Car HAS-A reference of Engine.
public Car(String carName, String carModel, String manufacturer, Engine engine) {
super();
this.carName = carName;
this.carModel = carModel;
this.manufacturer = manufacturer;
engine = new Engine();
}
// getter and Setter
} |
- Aggregation:
o Aggregation can be called the HAS-A relationship.
o When two objects are loosely coupled or we can say when one
object is not dependent on another object is called Aggregation.
o E.g. We have two objects. The first one is College and the
second one is Student. If college gets destroyed still Student objects can
survive independently.
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package simplifiedjava.crackedInterview; public class Student {
private int id;
private String name;
private String standard;
// getters and Setters method. } package simplifiedjava.crackedInterview;
import java.util.ArrayList; import java.util.List;
public class College {
List<Student> studentList = new ArrayList<Student>();
// add and remove Students.
} |
What is the difference between Composition and Aggregation?
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Composition |
Aggregation |
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1. |
Tightly couple relationship. |
Loosely coupled relationship. |
Is Java Pass by value or Pass by
reference. How will you prove java is call by value?
- Java is Call by Value not a Pass by reference.
- We will illustrate with the examples below.
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package simplifiedjava.crackedInterview; public class Addition {
int num1 = 100; int num2 = 0;
public static void main(String[] args) {
Addition add = new Addition();
System.out.println("Before Adding Numbers : "+ add.num1);
add.addNumber(add.num1);
System.out.println("After Adding Numbers : "+ add.num1); }
public void addNumber(int num2) {
num2 = num2 + 100;
} }
OUTPUT:
Before Adding Numbers : 100 After Adding Numbers : 100 Explaination : In the above program, we have passed integer numbers and trying to add 100. But the change remained in addNumber() function not in main(). package simplifiedjava.crackedInterview; public class Addition { int num1 = 100;
public static void main(String[] args) { Addition add = new Addition();
System.out.println("Before Addition " + add.num1);
add.addNumberWithObject(add);
System.out.println("After Addition " + add.num1); }
public void addNumberWithObject(Addition addCopy) {
addCopy.num1 = 200;
} } OUTPUT :
Before Addition 100 After Addition 200
Explanation: We have passed the reference variable as a value so
the value of num1 got changed. |
- Java interview questions and answers all MNC - Click here
- Basic core java interview questions and answers for freshers - Click here
- Core java interview questions for 3 years experience - Click here
- Core java interview questions and answers for 3-5 years exp - Click here
- Core java interview questions and Answers for 5 - 7 Years exp - Click here
- Basic Java Interview Questions and Answers - Click here
- Java interview questions and answers on oops - Click here
- Java interview questions and answers on Strings - Click here
- Java interview questions on exception handling - Click here
- Interview questions on multithreading in java for experienced - Click here
- Interview questions on serialization in java for experienced - Click here
- Interview questions on inner class in java for experienced - Click here
- Interview questions on Collections in java for experienced - Click here
Upcoming questions in next post:
11. Which is the top most Parent class in Java? What the methods of Object Class?
12. What is the role of break and continue keywords in java.
13. Is NULL keyword in java.
14. What is Actual Parameter and what is formal paramter?
15. What is the difference between Local variable and Instance variable.
16. What is the difference between Instance variable and Class Variable.
17. What are the uses of this keywords. Where it is applicable and what are the rules to use these two keywords.
18. What are the uses of super keywords. Where it is applicable and what are the rules to use these two keywords.
19. What are the access specifiers and its scope?
20. Can we use static member inside non-static area.
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Thank you techies for visiting this blog. I hope you enjoyed this blog and got more technical knowledge. I have tried to cover all types of questions and provided examples tested on eclipse as much as I can. Guys, please don’t just mug up the questions and answers. Try to clear your concepts with examples. Try to write a code on eclipse once you read the concepts. It will help you to memorize the concepts for a very long time. Simultaneously you will be prepared for interview programs as well. It will help you to survive in the IT sector for a long time. It may be easy to crack an interview but it's really tough to survive in the IT industry with inadequate knowledge and skills. I have collected all the questions from actual interviews attended by my friends, colleagues, college mate and classmate. I have covered frequently asked questions as well as challenging questions. I have included many programs to understand the concept thoroughly. I will try to explain the concept with the help of a real-time program in eclipse. You can share more questions which are not covered in this blog or post. Always welcome your suggestions and queries. I will definitely try to resolve it. Please comment your queries and new set of questions under the comment sections. I will create a new post for those questions.
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