Core Java Interview Quiestions

• Java History and Introduction
1. What is java?
2. What are java features?
3. List the different version of java and which is current version of software
4. What is the difference JDK, JRE, JVM and JIT?
5. What is JVM? Why is Java called the Platform Independent Programming Language?


• Data type and variables
1. What is data type?
2. What are the different types of data types?
3. List the primitive data types with size and range
4. What is a variable?
5. What is declaration and initialization variable?
6. Explain about local, instance and static variables?
7. Can we inherit local variable? If no, why?
8. Can we access local variable with object reference?
9. Can we declare local variable as static?
10. Can we declare local variable as final?
11. Can we use any access modifiers on local variable?
12. Explain about default value, and list the default value for each primitive data types and what is the default value for non-primitives?
13. Will compiler assign a default value to local variable?
14. What are pass by reference and pass by value?
15. What is the difference between variable and reference variable?
16. What is the naming convention fallowed to declare variables (non-constant and constant variables)?
17. What is meant be redeclaration and re-initialization, explain?


• Operators
1. List the different type of operators that java supports
2. What is difference between post and pre increment?
3. What is difference between post and pre decrement?
4. What is difference between && and & operator (single AND and double AND)?
5. What is difference between || and | operator (single OR and double OR)?
6. Explain ternary operator with syntax and example


• Condition statement
1. What is the syntax of if explain with example?
2. What is the syntax of if-else explain with example?
3. What is the syntax of else-if explain with example?
4. What is nested if explain with example
5. Explain switch statement with syntax
6. What is the difference between else-if and switch?


• Condition statement
1. What is the syntax of if explain with example?
2. What is the syntax of if-else explain with example?
3. What is the syntax of else-if explain with example?
4. What is nested if explain with example
5. Explain switch statement with syntax
6. What is the difference between else-if and switch?


• Loops
1. Explain for loop with syntax
2. Explain while loop with syntax
3. Explain do-while loop with syntax
4. What is the difference between for and while loop?
5. What is the difference between do-while and while loop?
6. What is break statement and where can we use break statement?


• Methods
1. What is a method?
2. What are the advantages of method?
3. What is method recursion explain with an example?
4. Can we have multiple return statements in the method
5. Can we return multiple values from the method?
6. What is method recursion explain with an example?
7. What is the naming convention fallowed to declare method?
8. Can we name the method name same as the class name?


• Class and Object
1. What is a class?
2. What is the object?
3. How to create an object?
4. Can we create a class as static?
5. Can we create a class as final?
6. Can we create a class as private?
7. Which all access modifiers can be used to declare the class
8. What is the naming convention fallowed to declare the class?
9. Can a .java file have multiple classes?
10. Can we have main method in multiple classes of same .java file? If so, which main method will get executed?
11. What should be the file name, if there are multiple class in a single .java file?
12. Can the class name and .java file name be different?
13. What is singleton class?
14. How can we make a class as singleton?
15. What is im-mutable object?
16. How can we create a im-mutable class?


• Class members
1. What are class members?
2. What is a difference between static and non-static members?
3. How to access static and non-static members?
4. Explain the memory allocation for both static and non-static members?
5. When does static members load into memory?
6. Can I access the static members using object or reference variable?
7. Can we access local variables outside the class? If no, why?
8. Can we decalre the local variables as static?


• Blocks
1. What is SIB and IIB?
2. What is the difference between SIB and IIB?
3. Can we have multiple SIB’s and IIB’s in the class? If so, what will the order of execution?
4. If the class contains SIB, IIB and constructor, which will execute first (or order of execution) when we create the first object?
5. If there is SIB in main class, which will execute first? SIB or main method
6. Can we write SIB inside the method or constructor?


• Inheritance
1. What is inheritance?
2. Explain inheritance with any inbuilt example
3. What are the different types of inheritance explain each with example?
4. What are the advantages of inheritance?
5. Can we inherit the static members? If no, explain why?
6. Can the child class access parent class static members?
7. Can we inherit final members of a class?
8. Can we inherit the final class?
9. Can we inherit the constructor? If no, explain why?
10. Can we inherit the private members?
11. Can we inherit the blocks?
12. Why does java, does not support multiple inheritance?


• Constructor
1. What is a constructor?
2. What are the different types of constructors?
3. What are the advantages of constructor?
4. What is parameterized constructor?
5. What is the difference between default constructor and zero parameterized constructor?
6. Why do we need a parameterized constructor?
7. What is constructor overloading?
8. Can we declare the constructor as final?
9. Can we declare the constructor as static?
10. Can we declare the constructor as abstract?
11. Can we declare the constructor as private?
12. What is constructor chaining?
13. Explain constructor chaining?
14. What is the difference between this and super?
15. Can a constructor have an empty return statement?
16. What will happen if we write a return type to a constructor?
17. Can we inherit the constructor? If no, why?
18. Can we over-ride the constructor? If no, why?
19. What is constructor recursion?


• Abstraction
1. What is abstract class?
2. What is abstract method?
3. Can we create the object of abstract class?
4. Can we declare the abstract method as static? If no, why?
5. Can we declare the abstract method as final? If no, why?
6. Can we declare the abstract method as private? If no, why?
7. Can we declare the abstract class final? If no, why?
8. Can abstract class have constructor?
9. What is the use of abstract class and abstract methods?
10. Can an abstract class have only abstract methods?
11. Can an abstract class have only concrete methods?
12. Can we declare the empty class as abstract?
13. Can we achieve 100% abstraction using abstract class?
14. Can we have static and non-static members declared in the abstract class? How can we access them?
15. What type of variables and methods can be declared inside the abstract class?
16. What is interface?
17. What type of variables and methods can be declared inside the interface?
18. What is functional interface?
19. What is marker interface?
20. Can we inherit more than one interface to the class?
21. Can an interface inherit another interface? If yes, how?
22. Can we declare concrete methods inside the interface? If yes, what type of concrete methods can be declared?
23. What type of variables can be declared inside the interface?
24. Can we override the default methods of interface?
25. What type of access modifiers can be used inside the interface?
26. What is the difference between abstract class and interface?
27. Can we declare the constructor inside the interface? If no, why?
28. Can we achieve 100% abstraction using interface? If yes, how?
29. What is abstraction?
30. What is the advantage of abstraction?


• Polymorphism
1. What is polymorphism?
2. What is over loading?
3. What is over riding?
4. What is the difference between over loading and overriding?
5. What is dynamic and static binding?
6. What is early and late binding?
7. What are the rules for overriding?
8. Can we override the static method? If no, why?
9. Can we override the final method? If no, why?
10. Can we overload the static method?
11. Can we overload the final method?
12. Can we override the main method? If no, why?
13. Can we overload the main method? If yes, then which method will be called when we run the program?


• Encapsulation
1. What is encapsulation?
2. Explain how can we achieve encapsulation in java?
3. Give the example for encapsulation?


• Casting
1. What is casting?
2. What are different types of casting does java support? Explain each with example
3. What is implicit casting?
4. What is explicit casting?
5. What is up-casting?
6. What is down-casting?
7. What is the use of up-casting?
8. Why do we need to do down-casting?
9. What is direct down casting? What will happen if we do direct down casting in java without upcasting?
10. Can we use parent type reference variable to store the child object? If yes, what is advantage of it?
11. Can we store the parent object into child type reference variable?
12. When do we get a ClassCastException?


• Access, non-access modifiers and packages
1. What are access modifiers?
2. What is the use of private, default, protected and public accesses modifiers?
3. Can we access protected members outside the package? If yes, how can we access?
4. Can we use access modifiers on local variables?
5. Can we use access modifiers on blocks?
6. What access modifiers can be used to declare the class?
7. Why main method should be public?
8. What will happen if declare the main method as private?
9. What is the use of final keyword?
10. What all can be declared as final in java?
11. What will happen if we declare the variable as final?
12. What will happen if we declare the method as final?
13. What will happen if we declare the class as final?
14. What is the use of static keyword?
15. What can be declared as static in java? What will happen if the member is declared as static?
16. What is transient?
17. Give an example for inbuilt final classes?
18. Give an example for inbuilt abstract classes?


• Object class
1. What is Object class?
2. What are the different methods present in object class?
3. What is the use of toString( ) method?
4. How can we compare two objects?
5. Why do we need to over-ride the equals() and hashCode() method?
6. What is cloning in java?
7. How to clone the objects in java?
8. What is cloneable?
9. What is the difference between == and equals( )?
10. What is hash code, in java?
11. How to create an object without new keyword?
12. What is diamond problem?


• String
1. What is String?
2. List important String class methods?
3. What is the difference between comparing the string object using == operator and equal method?
4. Is the String class final? If yes, why is it declared as final?
5. What is the difference between String, StringBuffer and StringBuilder?
6. Can we override the string class methods? If no, why?
7. What is the difference between append and concat method?



• Wrapper class
1. What are wrapper class?
2. Explain the hierarchy of wrapper class?
3. What is boxing?
4. What is unboxing?
5. What is parsing?
6. Can we parse String into char?
• Array
1. What is an array?
2. How to get the size of array?
3. What are the different ways to declare the array?
4. What are the advantages of array?
5. Why does main method accept String array, and not any other?


• Exception handling
1. What is exception?
2. How to handle the exception?
3. List the exception that you have come across in day-to-day coding along with scenario
4. Can we have multiple catch block to single try block?
5. Can we have multiple finally block to single try block?
6. What is finally?
7. Can we have multiple try block to single catch or finally block?
8. Can we have try-catch or try-catch-finally block inside a try block?
9. Can we have try-catch or try-catch-finally block inside the catch block?
10. Can we have try-catch or try-catch-finally block inside the finally block?
11. What is a difference between final, finally and finalize?
12. Explain about throw keyword
13. Explain about throws keyword
14. What is the difference between throw and throws?
15. What are the different types of Exception?
16. What is Runtime Exception / un-checked Exception?
17. What is compile time Exception / checked Exception?
18. List few in-built method which throw the checked exception
19. What is the difference between checked and un-checked exception?
20. What is Error?
21. What is Throwable?
22. What is the difference between Error and Exception?
23. What is custom exception? Or What is user defined exception?
24. How to create a custom un-checked exception?
25. How to create custom checked exception?


• Collection Framework
1. What is a Framework?
2. What is a difference between Collection and array?
3. What is Collection?
4. How to represent the hierarchy of Collection?
5. What is the difference between add(Object ref) and add(int index, Object ref) method?
6. What is the difference between add(int index, Object ref) and set(int index, Object ref) method?
7. List the methods of ArrayList
8. List the methods of LinkedList
9. What is the difference between ArrayList and LinkedList?
10. What is the difference between Iterator and ListIterator?
11. What is the difference between size(), length() and length?
12. What is the difference between Vector and ArrayList?
13. Explain about Enumeration interface
14. What is List?
15. What is Set?
16. What is the difference between List and Set?
17. List the methods of HashSet?
18. What is the difference between HashSet and LinkedHashSet?
19. What is the difference between HashSet, LinkedHashSet and TreeSet?
20. What is Comparator?
21. What is Comparable?
22. What is the difference between Comparator and Comparable?
23. What is Queue in java Collection
24. What is Priorityqueue?
25. What is the difference between peek and poll in queue?
26. What is Map?
27. How to represent the hierarchy of Map?
28. What is Entry?
29. What is EntrySet?
30. List the method of HashMap
31. What is the difference between HashMap and LinkedHashMap?
32. What is the difference between HashMap and HashTable?
33. What is the difference between HashMap and TreeMap?


• Stream and Lambda
1. What is Lambda expression?
2. What is functional interface?
3. What are the advantages of Lambda expression?
4. What is Function?
5. What is Predicate?
6. What is Consumer?
7. What is Supplier?
8. What is a Stream API?
9. What is the difference between Stream and Collection?
10. What is the use of map() method in Stream, explain with example
11. What is the use of filter() method in Stream, explain with example
12. What is the use of flatMap() method
13. What is the difference between map() and flatMap()


• Threads
1. What is a Thread?
2. What are the different ways to create thread? Explain each way with an example
3. Explain the life cycle of Thread?
4. What is the use of sleep method?
5. What is the use of wait method?
6. What is the difference between sleep and wait?
7. What does notify and notifyAll method does?
8. What is the difference among three wait methods?
9. What is volatile?
10. Can we use volatile keyword on methods and constructors?
11. What is synchronization?
12. How to achieve synchronization in java?
13. What is thread safe?
14. What is parallel execution?
15. What is the difference between parallel and serial execution?

JDBC

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Servlets

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Hibernate

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SpringCore

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SpringMVC

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SpringSecurity

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SpringBoot

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LogicalPrograms

• Simple Programs Java fundamentals
1. WAP to find sum of two numbers
2. WAP to find the average of three integer numbers
3. WAP to find the area of a circle
4. WAP to find circumference of a circle
5. WAP to find the percentage of a student
6. WAP to find the sum of four numbers
7. WAP to calculate the percentage of the student
8. WAP to calculate the discount price
9. WAP to calculate the service tax
10. WAP to print On-road price of the car, were it has 18.5% of road tax and 12.9% insurance of ex-showroom price of the car
11. WAP to swap two numbers using temporary variable
12. WAP to swap two numbers without using temporary variable
13. WAP to print if the number is odd or even
14. WAP find the largest of three numbers
15. WAP to find if the given number is divisible by both 4 and 7
16. WAP to print the grade of the student, with respect to scored percentage
17. WAP to print BMI result of a person for the calculated BMI value
18. WAP to print the numbers from 1 to 10
19. WAP to print the numbers from 10 to 1
20. WAP to print if the number if odd or even from 1 to 10
21. WAP to print the numbers from 1 to 200, who are divisible by both 3 and 5
22. WAP to print only odd numbers from 1 to 100, which are divisible by 7
23. WAP to print if the given number is prime or not
24. WAP to print the prime numbers in the given range
25. WAP to find the sum of n numbers
26. WAP to find the product of n numbers
27. WAP to find the factorial of given number
28. WAP to find the fibonacci series of given number
29. WAP to reverse the given number
30. WAP to count number of digits present in the given number