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Java Developer Interview Questions

  • OOPicon
  • JVMicon
  • Java Coreicon
  • Java Collections Frameworkicon
  • Java 8icon
  • I/O Streams in Javaicon
  • Serializationicon
  • Multithreadingicon
  • Reactive Programmingicon
  • Servlets, JSP, JSTLicon
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OOP

  • What is OOP ?
  • What are the basic principles of OOP ?
  • What is "encapsulation" ?
  • What is "inheritance" ?
  • What is "polymorphism" ?
  • What is "abstraction" ?
  • What is "messaging" ?
  • Tell us about the basic concepts of OOP: “class” , “object” , “interface” .
  • What are the advantages and disadvantages of the object-oriented approach to programming?
  • What do the expressions “is” and “has” mean in terms of OOP principles?
  • What is the difference between composition and aggregation ?
  • What is static and dynamic binding ?

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JVM

  • What is the JVM responsible for?
  • Classloader
  • Run-time data areas
  • Frames
  • Execution Engine
  • Useful links

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Java Core

  • What is the difference between JRE, JVM and JDK?
  • What access modifiers are there?
  • What does the final keyword mean?
  • What values ​​are default variables initialized to?
  • What do you know about the main() function?
  • What logical operations and operators do you know?
  • What is the ternary select operator?
  • What bitwise operations do you know?
  • Where and for what is the abstract modifier used?
  • Define the concept of “interface” . What default modifiers do fields and interface methods have?
  • How is an abstract class different from an interface? When should you use an abstract class and when should you use an interface?
  • Why do some interfaces not define methods at all?
  • Why can't you declare an interface method with the final modifier?
  • What has a higher level of abstraction - a class, an abstract class or an interface?
  • Can an object access a private class variable? If yes, then how?
  • What is the order in which constructors and initialization blocks are called, taking into account the class hierarchy?
  • Why are initialization blocks needed and what are they?
  • To which Java constructs does the static modifier apply?
  • Why are static initialization blocks used in Java?
  • What happens if an exception occurs in the initialization block?
  • What exception is thrown when an error occurs in a class initialization block?
  • Can a static method be overridden or overloaded?
  • Can non-static methods overload static ones?
  • Is it possible to narrow the access level/return type when overriding a method?
  • Is it possible to change when overriding a method: access modifier; return type; type of argument or number of arguments; names of arguments or their order, remove, add, change the order of elements in the throws section?
  • How to access overridden methods of a parent class?
  • Is it possible to declare a method abstract and static at the same time?
  • What is the difference between a class instance member and a static class member?
  • Where is initialization of static/non-static fields allowed?
  • What types of classes are there in java?
  • Tell us about nested classes. In what cases are they used?
  • What is a "static class" ?
  • What are the features of using nested classes: static and internal? What is the difference between them?
  • What is a "local class" ? What are its features?
  • What are "anonymous classes" ? Where are they used?
  • How can I access a field in an outer class from a nested class?
  • What is the assert statement used for?
  • What is a garbage collector for?
  • How does the garbage collector work?
  • What types of garbage collectors are implemented in the HotSpot virtual machine?
  • Describe the algorithm of operation of a garbage collector implemented in the HotSpot virtual machine.
  • What is finalize() ? Why is it needed?
  • What happens to the garbage collector if the finalize() method takes a noticeably long time to complete, or if an exception is thrown during execution?
  • What is the difference between final , finally and finalize() ?
  • What is Heap and Stack memory in Java? What's the difference between them?
  • Is it true that primitive data types are always stored on the stack, and instances of reference data types are always stored on the heap?
  • How are variables passed to methods, by value or by reference?
  • Tell us about type casting. What is type demotion and promotion?
  • When might a ClassCastException be thrown in an application?
  • What are literals?
  • What is autoboxing in Java and what are the rules for packing primitive types into wrapper classes?
  • What are the features of the String class?
  • What is a "string pool"?
  • Why String an immutable and finalized class?
  • Why is char[] preferable to String for storing password?
  • Why is String a popular key in HashMap in Java?
  • What does the intern() method do in the String class?
  • Is it possible to use strings in a switch construct?
  • What's the main difference between String , StringBuffer , StringBuilder ?
  • What is the Object class? What methods does it have?
  • Tell us about cloning objects.
  • What is the difference between superficial and deep cloning?
  • Which cloning method is preferable?
  • Why is the clone() method declared in the Object class and not in the Cloneable interface?
  • Define the concept of “constructor”.
  • What is a "default constructor" ?
  • What is the difference between default, copy and parameter constructors?
  • Where and how can you use a private constructor?
  • Tell us about loader classes and dynamic class loading.
  • What is Reflection ?
  • Why is equals() needed? How is it different from the == operation?
  • equals() generates an equivalence relation. What properties does such an attitude have?
  • If you want to override equals() , what conditions must be satisfied for the overridden method?
  • Rules for overriding the Object.equals() method.
  • What is the relationship between hashCode() and equals() ?
  • If equals() is overridden, are there any other methods that should be overridden?
  • What happens if you override equals() without overriding hashCode() ? What problems might arise?
  • How are hashCode() and equals() methods implemented in the Object class?
  • What is hashCode() method for?
  • Rules for overriding the Object.hashCode() method.
  • Are there any recommendations on what fields should be used when calculating hashCode() ?
  • Can different objects have the same hashCode() ?
  • If the class Point{int x, y;} implements equals(Object that) {(return this.x == that.x && this.y == that.y)} method, but makes the hash code in the form int hashCode() {return x;} , then will such points be correctly placed and retrieved from HashSet ?
  • Can different objects (ref0 != ref1) have ref0.equals(ref1) == true ?
  • Can different references to the same object (ref0 == ref1) have ref0.equals(ref1) == false ?
  • Is it possible to implement equals(Object that) {return this.hashCode() == that.hashCode()} method like this?
  • equals() requires checking that the argument equals(Object that) is the same type as the object itself. What is the difference between this.getClass() == that.getClass() and that instanceof MyClass ?
  • Is it possible to implement the equals() method of MyClass class like this: class MyClass {public boolean equals(MyClass that) {return this == that;}} ?
  • There is a class Point{int x, y;} . Why is hash code 31 * x + y preferable to x + y ?
  • Describe the hierarchy of exceptions.
  • What types of exceptions in Java do you know, how do they differ?
  • What is checked and unchecked exception ?
  • Which operator allows you to force an exception to be thrown?
  • What does the throws keyword mean?
  • How to write your own ("custom") exception?
  • What types of unchecked exception exist?
  • What is Error ?
  • What do you know about OutOfMemoryError ?
  • Describe the operation of the try-catch-finally block.
  • What is the try-with-resources mechanism?
  • Is it possible to use a try-finally block (without catch )?
  • Can one catch block catch multiple exceptions at once?
  • Is the finally block always executed?
  • Are there situations where a finally block will not be executed?
  • Can the main method throw an exception externally, and if so, where will this exception be handled?
  • Suppose there is a method that can throw IOException and FileNotFoundException in what order should the catch blocks go? How many catch blocks will be executed?
  • What are generics ?
  • What is “internationalization” , “localization” ?

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Java Collections

  • What is a "collection" ?
  • Name the main JCF interfaces and their implementations.
  • Arrange the following interfaces in a hierarchy: List , Set , Map , SortedSet , SortedMap , Collection , Iterable , Iterator , NavigableSet , NavigableMap .
  • Why is Map not Collection while List and Set are Collection ?
  • What is the difference between java.util.Collection and java.util.Collections classes?
  • What is “fail-fast behavior”?
  • What's the difference between fail-fast and fail-safe?
  • Give examples of iterators that implement fail-safe behavior
  • What is the difference between Enumeration and Iterator .
  • How are Iterable and Iterator related?
  • How are Iterable , Iterator and “for-each” related to each other?
  • Compare Iterator and ListIterator .
  • What happens when you call Iterator.next() without first calling Iterator.hasNext() ?
  • How many elements will be skipped if Iterator.next() is called after 10 calls Iterator.hasNext() ?
  • How will the collection behave if iterator.remove() is called?
  • How will an already instantiated iterator for collection behave if collection.remove() is called?
  • How to avoid ConcurrentModificationException while iterating over a collection?
  • Which collection implements the FIFO service discipline?
  • Which collection implements the FILO service discipline?
  • What is the difference between ArrayList and Vector ?
  • Why did they add ArrayList if there was already Vector ?
  • What is the difference between ArrayList and LinkedList ? In what cases is it better to use the first one, and in what cases the second one?
  • What is faster ArrayList or LinkedList ?
  • What is the worst running time for the contains() method on an element that is in LinkedList ?
  • What is the worst running time for the contains() method on an element that is in ArrayList ?
  • What's the worst running time for the add() method on LinkedList ?
  • What's the worst running time for the add() method on ArrayList ?
  • Need to add 1 million elements, what structure are you using?
  • How do you remove elements from ArrayList ? How does the size of ArrayList change in this case?
  • Propose an efficient algorithm for removing multiple adjacent elements from the middle of a list implemented by ArrayList .
  • How much additional memory is needed when calling ArrayList.add() ?
  • How much additional memory is allocated when calling LinkedList.add() ?
  • Estimate the amount of memory for storing one byte primitive in LinkedList ?
  • Estimate the amount of memory for storing one byte primitive in ArrayList ?
  • For ArrayList or for LinkedList is the operation of adding an element to the middle ( list.add(list.size()/2, newElement) ) slower?
  • The implementation of ArrayList class has the following fields: Object[] elementData , int size . Explain why you should store size separately if you can always take elementData.length ?
  • Compare the Queue and Deque interfaces.
  • Who extends whom: Queue extends Deque , or Deque extends Queue ?
  • Why does LinkedList implement both List and Deque ?
  • Is LinkedList a singly linked list, a doubly linked list, or a four linked list?
  • How to iterate through LinkedList elements in reverse order without using slow get(index) ?
  • What does PriorityQueue allow you to do?
  • Stack is considered "obsolete". What is recommended to replace it with? Why?
  • Why do we need HashMap if we have Hashtable ?
  • What is the difference between HashMap and IdentityHashMap ? What is IdentityHashMap for?
  • What is the difference between HashMap and WeakHashMap ? What is WeakHashMap used for?
  • WeakHashMap uses WeakReferences. Why not create SoftHashMap on SoftReferences?
  • WeakHashMap uses WeakReferences. Why not create PhantomHashMap on PhantomReferences?
  • LinkedHashMap - what is from LinkedList and what is from HashMap ?
  • How is SortedMap “sorted”, other than the fact that toString() displays all the elements in order?
  • How does HashMap work?
  • According to Knuth and Cormen, there are two main hash table implementations: open addressing based and chaining based. How is HashMap implemented? Why do you think this particular implementation was chosen? What are the pros and cons of each approach?
  • How does HashMap work when you try to store two elements into it by keys with the same hashCode() , but for which equals() == false ?
  • What is the initial number of buckets in HashMap ?
  • What is the estimate of the time complexity of operations on elements from HashMap ? Does HashMap guarantee the specified element fetch complexity?
  • Is it possible that HashMap will degenerate into a list even with keys that have different hashCode() ?
  • In what case can an element in HashMap be lost?
  • Why can't byte[] be used as a key in HashMap ?
  • What is the role equals() and hashCode() in HashMap ?
  • What is the maximum number hashCode() values?
  • What's the worst runtime for a get(key) method for a key that isn't in HashMap ?
  • What is the worst running time for the get(key) method for a key that is in HashMap ?
  • Why is it that even though a key in HashMap is not required to implement the Comparable interface, a doubly linked list can always be converted to a red-black-tree?
  • How many transitions occur when HashMap.get(key) is called on a key that is in the table?
  • How many new objects are created when you add a new element to HashMap ?
  • How and when does the number of buckets in HashMap increase?
  • Explain the meaning of the parameters in the HashMap(int initialCapacity, float loadFactor) constructor.
  • Will HashMap work if all added keys have the same hashCode() ?
  • How to iterate through all the keys Map ?
  • How to iterate through all Map values?
  • How to iterate through all key-value pairs in Map ?
  • What are the differences between TreeSet and HashSet ?
  • What happens if you add elements to TreeSet in ascending order?
  • How is LinkedHashSet different from HashSet ?
  • There is a special class for Enum java.util.EnumSet . For what? Why weren't the authors satisfied with HashSet or TreeSet ?
  • What ways are there to iterate over the elements of a list?
  • How can I get synchronized objects of standard collections?
  • How to get a read-only collection?
  • Write a single-threaded program that causes a collection to throw ConcurrentModificationException .
  • Give an example when any collection throws UnsupportedOperationException .
  • Implement the symmetric difference of two collections using the Collection methods ( addAll(...) , removeAll(...) , retainAll(...) ).
  • How to make a cache with “invalidation policy” using LinkedHashMap?
  • How can I copy the elements of any collection into an array in one line?
  • How to get List with all elements except the first and last 3 with one call from List ?
  • How to convert HashSet to ArrayList in one line?
  • How to convert ArrayList to HashSet in one line?
  • Make HashSet from the HashMap keys.
  • Make HashMap from HashSet<Map.Entry<K, V>> .

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Java 8

  • What innovations have appeared in Java 8 and JDK 8?
  • What is "lambda" ? What is the structure and usage features of a lambda expression?
  • What variables can lambda expressions access?
  • How to sort a list of strings using a lambda expression?
  • What is a "method reference"?
  • What types of method references do you know?
  • Explain the expression System.out::println .
  • What are "functional interfaces"?
  • What are the function interfaces Function<T,R> , DoubleFunction<R> , IntFunction<R> and LongFunction<R> for?
  • What are the functional interfaces UnaryOperator<T> , DoubleUnaryOperator , IntUnaryOperator and LongUnaryOperator for?
  • What are the functional interfaces BinaryOperator<T> , DoubleBinaryOperator , IntBinaryOperator and LongBinaryOperator for?
  • What are the Predicate<T> , DoublePredicate , IntPredicate and LongPredicate functional interfaces for?
  • What are the functional interfaces Consumer<T> , DoubleConsumer , IntConsumer and LongConsumer used for?
  • What are Supplier<T> , BooleanSupplier , DoubleSupplier , IntSupplier and LongSupplier functional interfaces for?
  • What is BiConsumer<T,U> functional interface for?
  • What is the functional interface BiFunction<T,U,R> needed for?
  • What is the BiPredicate<T,U> functional interface for?
  • What are functional interfaces like _To_Function needed for?
  • What are the function interfaces ToDoubleBiFunction<T,U> , ToIntBiFunction<T,U> and ToLongBiFunction<T,U> needed for?
  • What are the function interfaces ToDoubleFunction<T> , ToIntFunction<T> and ToLongFunction<T> for?
  • What are the functional interfaces ObjDoubleConsumer<T> , ObjIntConsumer<T> and ObjLongConsumer<T> for?
  • What is StringJoiner ?
  • What are default interface methods?
  • How to call default method of an interface in a class that implements this interface?
  • What is a static interface method?
  • How to call a static interface method?
  • What is Optional ?
  • What is Stream ?
  • What are the different ways to create a stream?
  • What is the difference between Collection and Stream ?
  • What is the collect() method used for in streams?
  • Why are forEach() and forEachOrdered() methods used in streams?
  • What are the map() and mapToInt() , mapToDouble() , mapToLong() methods used in streams?
  • What is the purpose of filter() method in streams?
  • What is the limit() method used for in streams?
  • What is the purpose of the sorted() method in streams?
  • What are flatMap() , flatMapToInt() , flatMapToDouble() , flatMapToLong() methods used in streams?
  • Explain about parallel processing in Java 8.
  • What ultimate methods of working with streams do you know?
  • What intermediate methods of working with streams do you know?
  • How to print 10 random numbers to the screen using forEach() ?
  • How can you display the unique squares of numbers using map() method?
  • How to display the number of empty lines using the filter() method?
  • How to display 10 random numbers in ascending order?
  • How to find the maximum number in a set?
  • How to find the minimum number in a set?
  • How to get the sum of all numbers in a set?
  • How to get the average of all numbers?
  • What additional methods for working with associative arrays (maps) appeared in Java 8?
  • What is LocalDateTime ?
  • What is ZonedDateTime ?
  • How to get current date using Date Time API from Java 8?
  • How to add 1 week, 1 month, 1 year, 10 years to current date using Date Time API?
  • How to get next Tuesday using Date Time API?
  • How to get the second Saturday of the current month using the Date Time API?
  • How to get the current time accurate to milliseconds using the Date Time API?
  • How to get the current local time accurate to milliseconds using the Date Time API?
  • How to define a repeatable annotation?
  • What is Nashorn ?
  • What is jjs ?
  • What class appeared in Java 8 for encoding/decoding data?
  • How to create a Base64 encoder and decoder?

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I/O Streams in Java

  • What is the difference between IO and NIO?
  • What features of NIO do you know?
  • What are "channels" ?
  • What types of I/O streams are there?
  • Name the main classes of I/O streams.
  • Which packages contain the I/O stream classes?
  • What subclasses of the InputStream class do you know and what are they for?
  • What is PushbackInputStream used for?
  • What is SequenceInputStream used for?
  • Which class allows you to read data from an input byte stream in the format of primitive data types?
  • What are the OutputStream class subclasses what are they for?
  • What kind of Reader class subclasses do you know why they are intended for?
  • What kind of Writer class subclasses do you know why they are intended for?
  • What is the difference between PrintWriter class from PrintStream ?
  • What is the difference and what does InputStream , OutputStream , Reader , Writer have in common?
  • Which classes allow you to convert bytic flows into symbolic and vice versa?
  • What classes allow you to accelerate reading/recording through the use of the buffer?
  • Which class is designed to work with the elements of the file system?
  • What methods of the File class do you know?
  • What do you know about the FileFilter interface?
  • How to choose all the elements of a certain catalog according to the criterion (for example, with a certain extension)?
  • What do you know about RandomAccessFile ?
  • What are the RandomAccessFile access mode?
  • What classes support reading and recording flows in a compressed format?
  • Is it possible to redirect the flows of standard input/output?
  • What symbol is a separator when specifying a path in the file system?
  • What is an “absolute path” and “relative path” ?
  • What is a "symbolic link" ?

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Serialization

  • What is "serialization" ?
  • Describe the process of serialization/deserization using Serializable .
  • How to change the standard behavior of serialization/deserization?
  • How to exclude fields from serialization?
  • What does the key word transient mean?
  • What influence do static and final field modifiers have on serialization
  • How to prevent serialization?
  • How to create your own serialization protocol?
  • What is the role of the serialVersionUID field in serialization?
  • When is it worth changing the value of the serialVersionUID field?
  • What is the problem of Singleton serialization?
  • What are the methods of monitoring the values ​​of the deserialized object

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Multiplying

  • Tell us about Java memory model?
  • What is "streamlines"?
  • What is the difference between “competition” and “parallelism” ?
  • What is "cooperative multitasking" ? What type of multitasking does Java use? What is this choice?
  • What is ORDERING , AS-SERIAL SEMANTICS , SEQUENTIAL CONSISTENCY , VISIBILITY , Atomicity , HAPPENS-BEFORE, MUTUAL EXCLUSION , SAFE PULICATION ?
  • What is the difference between the process from the flow?
  • What are “green flows” and are they in Java?
  • How can you create a stream?
  • How do Thread and Runnable differ?
  • What is the difference between start() and run() methods?
  • How to be forcibly launch a stream?
  • What is a “monitor” in Java?
  • Define the concept of "synchronization".
  • What are the ways of synchronization in Java?
  • In what states can a stream be?
  • Is it possible to create new specimens of the class while static synchronized method is performed?
  • Why maybe you need a private Myutex?
  • How do wait() and notify() / notifyAll() methods work?
  • What is the difference between notify() and notifyAll() ?
  • Why are the wait() and notify() methods only in a synchronized block?
  • What is the difference between the wait() method with the parameter and without the parameter?
  • What is the difference between Thread.sleep() and Thread.yield() methods?
  • How does Thread.join() method work?
  • What is Deadlock ?
  • What is Livelock ?
  • How to check whether the stream holds a monitor of a certain resource?
  • What object is synchronization when the static synchronized method is called?
  • Why is the keyword volatile , synchronized , transient , native ?
  • What are the differences between volatile and Atomic variables?
  • What are the differences between java.util.concurrent.Atomic*.compareAndSwap() and java.util.concurrent.Atomic*.weakCompareAndSwap() .
  • What does the priority of the stream mean?
  • What are “demon streams” ?
  • Is it possible to make the main stream of the program by a demon?
  • What does it mean to "sleep" a stream?
  • What is the difference between two Runnable and Callable interfaces?
  • What is FutureTask ?
  • What are the differences between CyclicBarrier and CountDownLatch ?
  • What is Race Condition ?
  • Is there a way to solve the problem of Race Condition ?
  • How to stop the flow?
  • Why is it not recommended to use the Thread.stop() method?
  • What happens when an exception is thrown out in the stream?
  • What is the difference between interrupted() and isInterrupted() ?
  • What is a "flows pool" ?
  • What size should there be a stream bullet?
  • What will happen if the turn of the flows bullet is already filled, but a new task is served?
  • What is the difference between submit() and execute() methods at the flows pool?
  • What are the differences between CTEK (Stack) and a heap (heap) in terms of multi -seating?
  • How to share data between two flows?
  • Which JVM launch parameter is used to monitor the size of the flow stack?
  • How to get a dump stream?
  • What is Threadlocal-cross ?
  • What are the differences between synchronized and ReentrantLock ?
  • What is ReadWriteLock ?
  • What is a “blocking method” ?
  • What is Framwork for Fork/Join ?
  • What is Semaphore ?
  • What is Double Checked Locking Singleton ?
  • How to create a streamline Singleton?
  • What are the useful objects useful?
  • What is Busy Spin ?
  • List the principles that you follow in multi -flow programming?
  • Which of the following statements about the flows is wrong?
  • Given 3 streams T1, T2 and T3? How to implement the execution in the sequence T1, T2, T3?
  • Write a minimum non -closing stack (only two methods - push() and pop() ).
  • Write a minimum non -closing stack (only two methods - push() and pop() ) using Semaphore .
  • Write the minimum non -closing Arraylist (only four methods - add() , get() , remove() , size() ).
  • Write a streamline classified class with the non -closing method BigInteger next() , which returns the elements of the sequence: [1, 2, 4, 8, 16, ...] .
  • Write the simplest multi -type limited buffer using synchronized .
  • Write the simplest multi -wind limited buffer using ReentrantLock .

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Reactive programming

  • What is reactive programming and how does it differ from procedural programming?
  • Explain the concept of data flows in reactive programming
  • What is Observer pattern and how does it underlie reactive programming?
  • Describe the role of Observable and Observer in reactive programming
  • What is Backpressure in the context of reactive programming?
  • Explain the difference between Hot and Cold Observable
  • What is the role of subscription in reactive programming?
  • How to unsubscribe from the stream to prevent memory leakage?
  • What are the operators in the Project Reactor and what are they used for?

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Servlets, JSP, JSTL

  • What is Servable ?
  • What are the advantages of the sergete technology over CGI (Common Gateway Interface)?
  • What is the structure of the web project?
  • What is the "Servant container" ?
  • Why do you need application servers, if there are servicemen containers?
  • How does the Servitov container control the servants of the Servut, when and what methods are caused?
  • What is a "deployment descriptor" ?
  • What actions do you need to do when creating the sergete?
  • In which case is it required to reduce the service() method?
  • Does it make sense to determine the constructor for the Servist? What is better to initialize data?
  • Why is it necessary to reduce the only init() method without arguments?
  • What are the most common tasks performed in the serviceman container?
  • What do you know about the Serny filters ?
  • Why are various Listener used in the Serlets?
  • When is it worth using the sergete filters, and when are the listeners?
  • How to implement the launch of the servlet simultaneously with the launch of the application?
  • How to process exceptions thrown out by another servlet in the application?
  • What is ServletConfig ?
  • What is ServletContext ?
  • What are the differences in ServletContext and ServletConfig ?
  • Why do I need the ServletResponse interface?
  • What is the ServletRequest interface for?
  • What is Request Dispatcher ?
  • How to call another Servable from one servlet?
  • What is the difference between sendRedirect() from forward() ?
  • Why are the seal attributes used and how is working with them?
  • How can DEADLOCK be allowed in Services?
  • How to get the real arrangement of the Servet on the server?
  • How to get information about the server from the Serlet?
  • How to get an IP address of a client on a server?
  • What class classes for the sergete do you know?
  • What are the differences between GenericServlet and HttpServlet ?
  • Why is HttpServlet class declared as an abstract?
  • What are the main methods in the HttpServlet class?
  • Is it worth worrying about multi -flow safety working with the Servites?
  • Which HTTP method is not unchanged?
  • What are the methods of sending data from the client to the server?
  • What is the difference between GET and POST methods?
  • What is the difference between PrintWriter and ServletOutputStream ?
  • Is it possible to use PrintWriter and ServletOutputStream at the same time?
  • Tell us about the SingleThreadModel interface.
  • What does url encoding mean? How to do this in Java?
  • What different methods of session management in the Servta do you know?
  • What are cookies ?
  • What methods for working with cookies are provided in the servlet?
  • What is the URL REWRITING ?
  • Why are encodeURL() and encodeRedirectURL() methods are needed and how are the methods?
  • What is a "session" ?
  • How to notify the object in the session that the session is invalid or ended?
  • What is an effective way to make sure that all servus are available only for the user with the right session?
  • How can we provide Transport Layer Security for our web application?
  • How to organize a database connection, provide journalization in a serpent?
  • What are the main features in the Servlet 3 specification?
  • What methods of authentication are available to the Serlet?
  • What is Java Server Pages (JSP) ?
  • Why do you need a JSP?
  • Describe how the pages are processed, starting from the request to the server, ending with the answer to the user.
  • Tell us about the stages (phases) of the JSP life cycle.
  • Tell us about the methods of the JSP life cycle.
  • What methods of the JSP life cycle can be redefined?
  • How can you prevent direct access to the JSP page from the browser?
  • What is the difference between the dynamic and static contents of JSP?
  • How to make a code in JSP?
  • What are the main types of JSP tags?
  • What do you know about JSP ( Action Tag and JSP Action Elements ).
  • JSP interaction - Servable - JSP .
  • What areas of visibility of variables exist in JSP?
  • What implicit, internal objects and methods are there on the JSP page?
  • What implicit objects are not available in a regular JSP page?
  • What do you know about PageContext and what are the advantages of its use?
  • How to configure initialization parameters for JSP?
  • Why is it not recommended to use Skillets (script elements) in JSP?
  • Is it possible to determine the class inside the JSP page?
  • What do you know about the language of JSP expressions (JSP Expression Language - EL)?
  • What types of EL operators do you know?
  • What are the implicit, internal JSP EL objects and their differences from JSP objects.
  • How to disable the possibility of using EL in JSP?
  • How to find out the type of HTTP method using JSP EL?
  • What is JSTL (JSP Standard Tag Library) ?
  • What groups of tags does the JSTL library consist of?
  • What is the difference between <c:set> and <jsp:useBean> ?
  • What is the difference between <c:import> from <jsp:include> and directives <%@include %> ?
  • How can JSP functionality be expanded?
  • What do you know about writing user JSP tags?
  • Give an example of using your own tags.
  • How to make lines transfer to HTML by JSP?
  • Why don't you need to configure standard JSP tags in web.xml ?
  • How can JSP be processed with pages?
  • How is error processing using JSTL?
  • How JSP is configured in the deployment descriptor.
  • Can JavaScript be used on a JSP page?
  • Is an object of a session on a JSP page always created, is it possible to turn off its creation?
  • What is the difference between JSPWriter and the Service PrintWriter ?
  • Describe the general practical principles of working with JSP.

To the table of contents

Databases

  • What is a “database” ?
  • What is a “database management system” ?
  • What is a "relational data model" ?
  • Define the terms “simple” , “composite” (composite) , “potential” ( alternative ”key (alternate) key.
  • What is the "primary key" (Primary Key) ? What are the criteria for his choice?
  • What is the "external key" ?
  • What is "normalization" ?
  • What are normal forms?
  • What is "denormardization" ? Why is it used?
  • What are the types of ties in the database? Give examples.
  • What are indexes ? Why are they used? What are their advantages and disadvantages?
  • What types of indices exist?
  • What is the difference between cluster and non -class indexes?
  • Does it make sense to index data that have a small amount of possible values?
  • When is the full scanning of the data set is more profitable for the index access?
  • What is a "transaction" ?
  • What are the basic properties of the transaction.
  • What are the levels of transaction isolation?
  • What problems can arise with parallel access using transactions?

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SQL

  • What is SQL ?
  • What are the SQL operators?
  • What does NULL mean in SQL?
  • What is a “temporary table” ? What is it used for?
  • What is a “view” and why is it used?
  • What is the general syntax of the SELECT operator?
  • What is JOIN ?
  • What are the JOIN types?
  • What is it better to use JOIN or subclasses?
  • What is the HAVING operator used for?
  • What is the difference between HAVING and WHERE operators?
  • What is ORDER BY operator used for?
  • What is GROUP BY operator used for?
  • How does GROUP BY process the NULL value?
  • What is the difference between GROUP BY and DISTINCT operators?
  • List the main aggregate functions.
  • What is the difference between COUNT(*) and COUNT({column}) ?
  • What does the EXISTS operator do?
  • Why are operators IN , BETWEEN , LIKE used?
  • What is the keyword UNION for?
  • What are the restrictions on data integrity in SQL?
  • What are the differences between PRIMARY and UNIQUE restrictions?
  • Can the value in the column, which is imposed on the restriction FOREIGN KEY , equal NULL ?
  • How to create an index?
  • What does the MERGE operator do?
  • What is the difference between DELETE and TRUNCATE operators?
  • What is a "stinging procedure" ?
  • What is the "trigger" ?
  • What is a "cursor" ?
  • Describe the difference between DATETIME and TIMESTAMP data.
  • For what numeric types are it unacceptable to use addition/subtraction operations?
  • What is the purpose of PIVOT and UNPIVOT operators in Transact-SQL?
  • Tell us about the main ranks of ranking in Transact-SQL.
  • Why are the INTERSECT operators used, EXCEPT in Transact-SQL?
  • Write a request ...

To the table of contents

JDBC

  • What is JDBC ?
  • What are the advantages of using JDBC?
  • What is JDBC URL?
  • What parts is JDBC from?
  • List the main types of data used in JDBC. How are they related to the types of Java?
  • Describe the main stages of working with the database using JDBC.
  • How to register a JDBC driver?
  • How to install a database connection?
  • What transaction insulation levels are supported in JDBC?
  • What are the database requests formed?
  • What is the difference between Statement from PrepareDstatement?
  • How is a database request and processing results?
  • How to call the stored procedure?
  • How to close the connection connection?

To the table of contents

Testing

  • What is "modular testing" ?
  • What is "integration testing" ?
  • How does integration testing differ from modular?
  • What are the types of test objects?
  • How is Stub different from Mock ?
  • What are "fixed" ?
  • What kind of fixed annots do Junit exist?
  • Why does Junit use @Ignore annotation?

To the table of contents

Journalism

  • What are the types of logs?
  • What parts does the LOG4J be journal consist of?
  • What is Logger in LOG4J?
  • What is Appender in LOG4J?
  • What is Layout in LOG4J?
  • List the levels of journaling in LOG4J? What is your priority.
  • What are the methods of configuration LOG4J?

To the table of contents

UML

  • What is UML ?
  • What is a “diagram” , “notation” and “metamodel” in UML?
  • What are the types of diagrams?
  • What types of relationships exist in the structural diagram of classes?

To the table of contents

XML

  • What is XML ?
  • What is DTD ?
  • How is the Well-Formed XML different from Valid XML ?
  • What is the " namespace " in XML?
  • What is XSD? What are its advantages over XML DTD?
  • What types exist in XSD?
  • What are the XML reading methods? Describe the strengths and weaknesses of each method.
  • When should you use DOM , and when SAX , Stax analyzers ??
  • What are the ways of recording XML?
  • What is JAXP ?
  • What is XSLT ?

To the table of contents

Design templates

  • What is a “design template” ?
  • What are the main characteristics of the templates.
  • Types of design templates.
  • Give examples of the main design templates.
  • Give examples of generating design templates.
  • Give examples of structural design templates.
  • Give examples of behavioral design templates.
  • What is Antipattern ? What antipatterns do you know?
  • What is Dependency Injection ?

To the table of contents

HTML Basics

  • What is HTML ?
  • What is Xhtml ?
  • What is DOCTYPE and why is it needed?
  • What is the <head> tag for?
  • What is the difference between <div> from <span> ?
  • How are comments in HTML?
  • How is the address of the document to go to?
  • How to make a link to the email address?
  • What is the <em> tag for?
  • What are the tags <ol> , <ul> , <li> for?
  • What are the tags <dl> , <dt> , <dd> for?
  • Why are the tags <tr> , <th> , <td> ?
  • Is it necessary to write an alt attribute in the <img> tag?
  • In which register is it better to write an HTML code?
  • What is Mnemonics (Entity)?

To the table of contents

Fundamentals of CSS

  • What is CSS ?
  • How do CSS mean comments?
  • What is a "selector" ?
  • List the main types of selectors.
  • What is Psevdoklass?
  • What are the attribute selectors?
  • What is the difference between #my and .my ?
  • What is the difference between margin and padding ?
  • What is the difference between the values ​​of 0 and auto in margin property?
  • What property does the background color set?
  • How to remove the emphasis for all links on the page?
  • What is clear property used for?
  • How to make a fat text in all elements <p> ?
  • How to set red color for all the elements having a class red ?

To the table of contents

Fundamentals of Web

  • What is www ?
  • What is W3C ?
  • What are the OSI model levels?
  • What is TCP/IP ?
  • What is UDP ?
  • What is the difference between TCP and UDP ?
  • What is a data transfer protocol? What protocols do you know?
  • What is HTTP and HTTPS ? How are they different?
  • What is FTP ?
  • What is the difference between the Get and Post methods?
  • What is MIME type ?
  • What is Web Server ?
  • What is Web Application ?
  • What is Application Server ?
  • What is the difference between Web Server and Application Server ?
  • What is Ajax ? How is this technology fundamentally arranged?
  • What is WebSocket ?
  • What is JSON ?
  • What is JSON scheme ?
  • What are cookies ?
  • What is a "session" ?
  • What is "authorization" and "authentication" ? How are they different?

To the table of contents

Apache kafka

  • What is Apache Kafka?
  • The main components of Kafka

The architecture of the components

  • Topic
    • Topic architecture
    • Настройки топика Kafka
  • Broker
    • Архитектура брокера
    • Настройки брокера Kafka
  • Producer
    • Архитектура продюсера
    • Настройки продюсера
    • Пример конфигурации Kafka Producer
  • Consumer
    • Архитектура консюмера
    • Настройки консюмера
    • Пример конфигурации Kafka Consumer

Kafka API

  • Основные API Kafka
  • Какова роль Producer API?
  • Какова роль Consumer API?
  • Какова роль Connector API?
  • Какова роль Streams API?
  • Какова роль Transactions API?
  • Какова роль Quota API?
  • Какова роль AdminClient API?

Kafka Consumer

  • Для чего нужен координатор группы?
  • Для чего нужен Consumer heartbeat thread?
  • Как Kafka обрабатывает сообщения?
  • Как Kafka обрабатывает задержку консюмера?
  • Для чего нужны методы subscribe() и poll()?
  • Для чего нужен метод position()?
  • Для чего нужны методы commitSync() и commitAsync()?

Other questions

  • Для чего нужен идемпотентный продюсер?
  • Для чего нужен интерфейс Partitioner?
  • Для чего нужен Broker log cleaner thread?
  • Для чего нужен Kafka Mirror Maker?
  • Для чего нужна Schema Registry?
  • Для чего нужен Streams DSL?
  • Как Kafka обеспечивает версионирование сообщений?
  • Как потребители получают сообщения от брокера?

Сравнение с другими компонентами и системами

  • В чем разница между Kafka Consumer и Kafka Stream?
  • В чем разница между Kafka Streams и Apache Flink?
  • В чем разница между Kafka и Flume?
  • В чем разница между Kafka и RabbitMQ?

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Additional materials

  • 4 толковых канала на Youtube про технические собеседования
  • A list of fancy questions I've been asked during the interviews I had
  • Job interview in English: как готовиться и что отвечать
  • Senior Engineer в поисках работы. О задачах на технических собеседованиях и теоретических вопросах
  • What to ask an interviewer during a tech interview
  • Spring Boot Interview Questions
  • Top Spring Framework Interview Questions
  • Spring Interview Questions
  • Hibernate Interview Questions

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Sources

  • Вопросы на собеседование Junior Java Developer
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