Core java interview questions and answers for beginners and professionals on Basics, OOPs, Methods, Overloading, Overriding, Inheritance, Polymorphism, Interfaces, Packages, Abstract classes, String handling, Exception handling, IO, Collections, Multithreading, Serialization and more.
Java interview questions
- why java is platform independent and jvm is platform dependent?
- List any five features of java?
- What all memory areas are allocated by JVM?
- What is difference between JDK, JRE and JVM?
- What is javac?
- Why java is not 100 object oriented language?
- What is the base class of all classes in java?
- What gives java its write once and run anywhere nature?
- What is classloader in java?
- Is empty .java file name a valid source file name?
- Can we overload main() method in java?
- Can we declare main() method as private or protected or with no access modifier?
- Can we declare main method as non static in java?
- Why main() method must be static?
- Can we change return type of main() method?
- Can we run java class without main() method?
- Difference between Object Oriented Programming and Procedural Programming.
- Difference between Object Oriented and Object based language.
- What is class in java?
- What is object in java?
- How to open a notepad in java?
- What is constructor?
- Default constructor
- Does constructor return any value in java?
- Is constructor inherited in java?
- Can you make a constructor final in java?
- Difference between constructor and method in java?
- How to copy values from one object to another java?
- How to overload constructor in java?
- can you create an object without using new operator in java?
- Constructor chaining in java
- Parameterized constructor in java
- Can we call subclass constructor from superclass constructor?
- What happens if you keep return type for a constructor?
- What is the use of private constructor in java?
- Can a constructor call another constructor java?
- What is static variable in java?
- What is static method in java?
- What is static block in java?
- What is this in java?
- What is aggregation in java?
- What is inheritance in java?
- Why multiple inheritance is not supported in java?
- How to implement multiple inheritance in java?
- Are interfaces also inherited from Object class?
- Why an interface cannot have constructor in java?
- How do you restrict a member of a class from inheriting to it’s sub classes?
- Can a class extend itself in java?
- Are constructors inherited in java?
- What happens if both superclass and subclass have a field with same name?
- Are static members inherited to subclasses in java?
- what are access modifiers in java?
- What are different types of access modifiers in java?
- What are non access modifiers in java?
- Can we use abstract and final both with a method?
- Can abstract class have final methods in java?
- Can we declare a class as private in java?
- Can we declare an abstract method as private?
- Can we declare a class as protected in java?
- what is final in java?
- What is final variable in java?
- What is final method in java?
- What is final class in java?
- What is blank final variable in java?
- What is static blank final variable in java?
- What is final parameter in java?
- Can we initialize blank final variable in java?
- Can we declare the main method as final?
- What is the use of final keyword in java?
- Can we change the state of an object to which a final reference variable is pointing?
- Difference between abstract method and final method in java?
- Can we change the value of an interface field?
- Can we declare constructor as final in java?
- What is runtime polymorphism in java?
- Can we achieve runtime polymorphism by data members?
- What is the difference between static binding and dynamic binding in java?
- What is abstraction in java?
- What is the difference between abstraction and encapsulation?
- What is encapsulation in java?
- What is polymorphism in java?
- Are true and false keywords in java?
- Can we declare local inner class as private?
- Is “abc” a primitive value?
- What is the priority of garbage collector thread?
- Is map collection in java?
- Which package is always imported by default?
- Can a class implement two interfaces with the same method signature?
- Can you declare an interface method static in java?
- Which one is faster among string stringbuffer and stringbuilder?
- What is method overloading in java?
- Can we declare an overloaded method as static and another one as non-static?
- Can overloaded methods be synchronized?
- Synchronized override method
- Can we declare overloaded methods as final?
- Can overloaded method be overridden?
- What is method overriding in java?
- Can static method be overridden?
- Difference between method overloading and overriding in java?
- Can we override private methods in java?
- Is it possible to override non static method as static method?
- What is interface in java?
- Can we declare an interface method static in java?
- Can an interface be declared final in java?
- What is marker interface and how we can create it?
- What is difference between abstract class and interface in java?
- What is abstract class in java?
- Why abstract class is used in java?
- Can abstract class have constructors in java?
- Can abstract class be final in java?
- Can we declare local inner class as abstract?
- what is an exception?
- How the exceptions are handled in java?
- What is the difference between error and exception in java?
- Can we keep other statements in between try catch and finally blocks?
- Explain the exception hierarchy in java?
- What are runtime exceptions in java?
- What is outofmemoryerror in java?
- What are checked and unchecked exceptions in java?
- What is the difference between classnotfoundexception and noclassdeffounderror in java?
- Will finally block get executed if return?
- Can we throw an exception without throws?
- What is rethrowing an exception in java?
- What is the use of throws keyword in java?
- What is exception propagation in java?
- Difference between throw and throws in java?
- What is finally in java?
- What is the difference between final finally and finalize in java?
- How to create customized exceptions in java?
- What is classcastexception in java?
- What is stackoverflowerror in java?
- What is the superclass of all exception classes?
- What is the use of printstacktrace method in java?
- What is arraystoreexception in java?
- Why string objects are immutable in java?
- How many ways we can create the string object?
- Why java uses the concept of string literal?
- String vs StringBuffer vs StringBuilder in java
- How to create immutable class in java?
- What is the purpose of toString() method in java?
- Is string a keyword in java?
- Is string a primitive type or derived type?
- What is string constant pool in java?
- What are mutable and immutable objects in java?
- What is string intern in java?
- Can we call string class methods using string literals?
- Can we change array size in java?
- What is an anonymous array in java?
- Difference between array and arraylist in java?
- What are jagged arrays in java?
- Can array size be negative in java?
- Java program to find duplicate elements in an array.
- Java program to find second largest element in an array of integers.
- Java program to check the equality of two arrays.
- Find all pairs of elements in an integer array whose sum is equal to a given number.
- Java program to find continuous sub array whose sum is equal to a given number
- Java program to find the intersection of two arrays
- Java program to separate zeros from non-zeros in an integer array
- Java program to find all the leaders in an integer array
- Java program to find a missing number in an integer array
- Java program to convert an array to ArrayList and an ArrayList to array
- Java program to count occurrences of each element in an array
- Java program to reverse an array without using an additional array
- Java program to remove duplicate elements from an array
- Java program to find union and intersection of multiple arrays
- Java program to find the most frequent element in an array
- What is multithreading?
- Difference between process and thread in java?
- What is thread in java?
- What is join method in java?
- What is the difference between sleep and yield method?
- Is it possible to start a thread twice in java?
- Can we call run method directly in java?
- What is daemon threads in java?
- Can we make the user thread as daemon thread if thread is started?
- Difference between thread start and run method.
- Why we call start method in thread?
- Which is a better way to create a thread in java?
- Can we override start method?
- Can we override run method?
- How to get current thread in java?
- What is synchronization?
- What is synchronized block in java?
- What is synchronized method in java?
- What is static synchronization in java?
- What is deadlock in java?
- What is starvation in java?
- ArrayList vs LinkedList vs Vector
- Iterator vs ListIterator vs Enumeration
- List vs Set Vs Map
- HashSet vs LinkedHashSet vs TreeSet
- HashMap vs LinkedHashMap vs TreeMap vs HashTable
- HashSet vs HashMap vs HashTable
- Collection vs collections in java
- Comparable vs Comparator interfaces
- What is garbage collection in java?
- What is garbage collector in java?
- Can an unreferenced objects be referenced again in java?
- What kind of thread is the garbage collector thread in java?
- what is serialization in java?
- what is Deserialization in java?
- What is transient keyword?
- Java hashcode and equals methods
- How HashMep works internally?
- How hashmap stores null key?
- How hashset works internally?