Java Interview Questions

    Basic core java Interview Questions And Preparation Guide

      Difference between HashMap and TreeMap with an Example

      Difference between the JRE and the JDK

      JIT Compiler

      How HashMap works in Java

      How to override hashCode method

      How TreeMap works in Java

      Shallow copy and Deep Copy

      Reading and Writing system properties in java

      How LinkedHashMap works in Java

      Statically Vs Dynamically typed Programming languages

      Difference between iterator and enumerator

      Difference between Iterator and ListIterator

      Calculate method execution time

      Examples to concatenate strings in Java

      Java stores in big-endian format

  Comparable Vs Comparator

      How IdentityHashMap Works in Java?

      Serialization

      Difference between HashMap and IdentityHashMap

      How HashTable works in Java

      Why Synchronization is costly operation

      Why get method is synchronized in Hashtable?

      Why Wait and Notify is in Object Class

      Dead lock Example

      Difference between HashMap and Hashtable

      How to traverse HashMap in Java

      Externalization

      Producer Consumer Problem

      How to traverse TreeMap in Java

      Create Memory leak in Java

      Is overriding of static methods possible in Java ?

      Object Creation and Destruction

      Can I access private variables in Java ?

      Is finally always execute in Java ?

      Features Of Java

      Garbage Collection

      Why to declare local variables as final inside methods?

      Sort HashMap by key and value

      Sort List of objects on multiple fields

      char array is proffered over strings to store passwords

      Relation between Method Overriding And Exception Handling

      How to create Immutable class

      How to solve Unsupported major.minor version 51.0?

      Serialization Vs Singleton

      Implement custom iterator in Java

      Provide for-each behavior to custom collection

      Explain different areas of Java Heap

      Is System.exit takes negative value?

      Sort elements of a list in predefined order

      Implement pooling functionality for connection objects

      Why do we require empty collections?

      Why do we require empty iterators?

     Difference between System.out and System.err

    Is Serializable class has any methods?

    How to see the serialVersionUID of serialized class?

    What happen if one of the members in the class doesn't implement Serializable interface?

    Can I apply transient keyword to methods?

    Is serializable class require default constructor while doing serialization and deserialization?

    Is Serialization saves super class fields?

    Can I customize serialization process?

    Restrict a class from serialization, but super class is serialized

    Implement Bijective Map

    How to resolve Circular Dependency Problem

    What is ReentrantLock?

    Non-Blocking Algorithms

    Implement Thread Pool in Java

    Why to use static factory methods over constructors

    When to use builder pattern

    Implement Singleton with Enum

    Can I Extend a class with only private constructors?

    Why to use Boolean.valueOf than Boolean constructor?

    Why should we avoid finalize method?

    Why to implement Comparable?

    Is operations on primitive types are atomic?

    What is null in Java?

    Can I pass null to append method of StringBuilder?

    Why and how to set JAVA_HOME

    Get elements of LinkedHashMap by access order?

    Implement LRU cache using LinkedHashMap

    Implement Array Iterator

    How to get the interfaces implemented by a class?

    Different ways to sort Array list in Java

    Initialize list in one line

    Merge generic arrays

    How to get shallow copy of array?

    Implement case insensitive map

    What is the problem with type erasure?

    Remove element at given index from array

    Redirect System out and error messages to files programmatically

    Implement a stream that writes to multiple streams

    Java is pass by value or pass by reference ?

    Why Generic types in Java are invariant?

    Populate one object from other object properties

     Can I declare an array, collection (or) object as volatile?

    Why should a private constructor throw an exception?

    Can a private constructor prevent sub-classing of class?

    How to bypass checked exception while creating object?

    Is array a primitive type or object in java?

    How to check an exception is checked or not?

    How to check given object is an array or not?

    How to get the system hash code of an object?

    Can a functional interface have more than one method?

    Arrays.asList() throws UnsupportedOperationException while removing element using iterator

    When Can I use ClassName.this

    Is Arrays.asList immutable

    How to create immutable list in Java?

    Open-closed principle design problem

    Threads: print characters of a string simultaneously

    Why an abstract class has a constructor?

    Can I call one constructor from another in java?

    Implement Runnable vs extends Thread

    How to break outer loop in Java?

    null and instanceof operator

    String interning

    Static and Dynamic class loading

    Different ways to dynamically load a class

    Class.forName vs ClassLoader.loadClass

    How the jdbc driver is loaded?

    Can I overload main method of a class?

    Can I throw an exception from static block?

    Does yield method releases the lock?

    Can I call a run method of thread class directly?

    java.util.Date vs java.sql.Date

      Disadvantages of Autoboxing

      How to count number of instances of a class?

      Why a collection doesn’t extend Cloneable or Serializable interfaces?

      Explain about WeakHashMap

      Class Name of anonymous class

      Annotations explained

      Is length property of array final?

      Can I define an array of size 0?

      Can I define an array with negative size?

      Why the interface variables are public, static, final by default?

      Why a non-static method can’t be referenced in static context?

      Get first element from a collection

      How to stop a thread in Java?

      How to pass method as a parameter in Java?

      Shuffle array lists in same fashion (java)

      How to shuffle an array?

      How to specify timeout to a thread?

      Remove elements of map while iterating?

      Default values of primitive fields

      What is the default value of Boolean field?

      Is null instance of anything?

      Iterate list in reverse order

      Can I use calloc and malloc as variable name in Java?

      Check whether a number is 32 bit integer or not

      How to get Original Hash code of the object?

      What is the use of Collections.emptyList in Java?

      Is Collections.emptyList() immutable?

      Is Collections.emptyList() singleton?

      List Capacity vs Size

      ArrayList: add: IndexOutOfBoundsException

      Check two lists contain same elements or not (order not required)

      How to pick random element from Set?

      Why Set do not have get(int index) method?

      Combine hashmaps with same type

      Can a non-void method compiles, run without return value?

      Get currently running threads in Java

      Can a Constructor throw an exception?

      Finalizer Attack in Java

      map vs flatMap

      Convert array of strings to a string

      Explicitly invoke the default implementation of a method

      Regular Expression: Remove all non-numeric characters from string

      Can a constructor in Java is private?

      What is |= stands for in Java?

      What is &= stands for in Java?

      Capitalize first letter of every word in string

      Can an Anonymous class has an explicit constructor?

      How Java handles Integer overflows and underflows?

      Thread.start() vs Runnable.run()

      Pass ArrayList to a method with varargs?

      Can I define synchronized methods in interface?

      How to define global variables in Java?

      Why does (a == (a = b)) not same as (a = b) == a?

      How to copy elements of ArrayList to other list?

      How to check given string represent integer or not?

      equals() vs Arrays.equals

      Convert List to a Map

      Java Bean vs POJO

      How many threads supported by Java?

      How to initialize long in Java?

      How to Initialize Multiple Variables to same value in Java?

      Extract digits from a string or text

      Remove first character of a string

      List: Replace element at specific index

      How to check whether a collection is null or empty?

      How to check whether a map is null or empty?

      Convert String to a character

      Get intersection of two sets

      Transform Map to Map

      How to initialize String array

      Split comma separated string to list of strings

      How to declare ArrayList with values?

      How to initialize string array?

      Implement re-try-catch

      NumberFormatException Explained

      Initial heap size set to a larger value than the maximum heap size

      Is below statement compile?

      Versioning History of Java

      Understanding ConcurrentModificationException in Java

      Java: Remove oldest entry from the map

      Synthetic constructs in Java

      What is bridge method in Java?

      How HashSet behave while adding a duplicate value?

      How to call a method asynchronously in Java?

      How method overloading works with null values in Java?

      Java: How to find maximum element from a collection?

      Java: How to find the minimum element in a collection?

      Java: Get the index of first occurrence of a substring

      Java: Get the index of last occurrence of a substring

      Java: Get all the indexes of occurrence of a substring

      Java: How to replace a value in ArrayList or LinkedList

      Why do we declare logger with static and final?

      Java: Remove single character at given index from a string

      Java: How to access this from Anonymous class?

      How to check the type of a variable in Java?

      Set a system property in command line

      How to get the capacity of ArrayList in Java?

      volatile reference vs Atomic references defined in java.util.concurrent.atomic package

      Check whether I have JDK or JRE in my system

      How to check whether string contain only whitespaces or not?

      How to call base class method from subclass overriding method?

      Can an interface extend multiple interfaces in Java?

      How to specify jar files in command line?

      Explain Loop inversion in Java

      instanceof operator behavior with interface and class

      Call the main method of one class from other class using reflection

      Check whether a class exists in the classpath or not

      How to get the name of calling class that invoke given method?

      Implement map using array as storage

      How to resolve NoClassDefFoundError?

      Jagged arrays in Java

      Get the length of longest row in a two dimensional jagged array in Java

       Quick guide to OutOfMemoryError in Java

      StackOverFlowError vs OutOfMemoryError in Java

      Different ways to iterate over a map using for-each loop

      How for-each or enhanced for loop works in Java?

      How to solve UnsupportedClassVersionError in Java?

      How to find the Java major and minor versions from a .class file?

      Can I run a class file that is compiled in lower environment?

      How to solve Error: Could not find or load main?

      float vs double in Java

      Quick guide to race condition in Java with examples

      How to read the file content using an iterator in Java?

      Implement a Closeable iterator in Java

      Quick guide to generate random data in Java

      What are the different cache eviction strategies?

      How to call super class method from sub class overriding method?

      Can an enum has abstract methods in Java?

      Can enum implement an interface in Java?

      What happen to the threads when main method complete execution

      Why System.out.println() is not throwing NullPointerException on null references?

      Why should we restrict direct access to instance properties?

      Closeable vs AutoCloseable in Java

      What is the behaviour of static final method in Java?

      How to check two double values for equality?

      Why to do explicit type casting from double to float conversion?

      When is a class or interface is initialized or loaded in Java?

      How to check two float values equality?

       How to check whether a class is loaded or not in Java?

      How to get a random element from Set?

      Extract the elements of specific type in a collection

      Method overloading ambiguity with null values in Java

      Quick guide to load balancers

      Constant folding in Java

      Quick guide to assertions in Java

      java.util.Date vs java.sql.Date

      How to break out of nested loops in Java?

      Implementation of Bag data structure in Java

      Scanner throws java.util.NoSuchElementException while reading the input

      How to get all the enum values in Java?

      Extend the thread to check it’s running status

      Implement retry handler for a task in Java

      Design an utility class to capture application metrics summary in Java

      Utility class to get primitive type from wrapper type and vice versa

      FNV hash algorithm implementation in Java

      Controlling Randomness in Java: Exploring the Role of Seeds in java.util.Random

      Program to create append only log file in Java

      Calculating initial capacity from expected size and load factor

      Implement a shared reentrant lock

      A Beginner's Guide to UUID Types

      Ensuring Platform-Independent Accuracy: A Guide to strictfp in Java

      Creating Case-Insensitive Maps in Java: Simplifying Lookups with Lowercase Keys