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- Too busy: Show appreciation to the debtor that keeps him busy, and politely ask them to settle the payment without any delaying as it is the best interest for him. Things to be considered before filing a lawsuit is Is yours claim large enough to...
- Though difference has been discussed briefly in above 2 points but in this in point we will figure difference in detail. Get method of ArrayList directly gets element on specified index. Hence, offering O 1 complexity in java. Get method of LinkedList iterates on nodes sequentially to get element on specified index. Hence, offering O n complexity in java. Use LinkedList when add and remove operations are more frequent than get operations in java. For more detail like complexity comparison of method please read : ArrayList vs LinkedList in java Collection interview Question 5.
- What are differences between ArrayList and Vector in java? Another very important collection framework interview question to differentiate between ArrayList and Vector in java.
- Structure java. ArrayList is index based structure in java. A java. LinkedList is a data structure consisting of a group of nodes which together represent a sequence. New node is created for storing new element in LinkedList in java. ArrayList is created with initial capacity of 10 in java. LinkedList does not implement RandomAccess interface in java. In LinkedList, data is accessed sequentially, so for obtaining data at specific index, iteration is done on nodes sequentially in java. Though difference has been discussed briefly in above 2 points but in this in point we will figure difference in detail. Get method of ArrayList directly gets element on specified index. Hence, offering O 1 complexity in java. Get method of LinkedList iterates on nodes sequentially to get element on specified index.
- Hence, offering O n complexity in java. Use LinkedList when add and remove operations are more frequent than get operations in java. For more detail like complexity comparison of method please read : ArrayList vs LinkedList in java Collection interview Question 5. What are differences between ArrayList and Vector in java? Another very important collection framework interview question to differentiate between ArrayList and Vector in java.
Top 10 Java Collections Interview Questions Answers For Beginners
Java Collections What are the basic interfaces of Java Collections Framework? Java Collections Framework provides a well designed set of interfaces and classes that support operations on a collections of objects. The most basic interfaces that reside in the Java Collections Framework are: Collection , which represents a group of objects known as its elements. Set , which is a collection that cannot contain duplicate elements. List , which is an ordered collection and can contain duplicate elements. Map , which is an object that maps keys to values and cannot contain duplicate keys. The Collection interface specifies groups of objects known as elements. Each concrete implementation of a Collection can choose its own way of how to maintain and order its elements.- The semantics and the implications of either cloning or serialization come into play when dealing with actual implementations. Thus, the concrete implementations of collections should decide how they can be cloned or serialized. What is an Iterator? The Iterator interface provides a number of methods that are able to iterate over any Collection. Each Java Collection contains the Iterator method that returns an Iterator instance. Iterators are capable of removing elements from the underlying collection during the iteration. What differences exist between Iterator and ListIterator? The differences of these elements are listed below: An Iterator can be used to traverse the Set and List collections, while the ListIterator can be used to iterate only over List.
- The Iterator can traverse a collection only in forward direction, while the ListIterator can traverse a List in both directions. The ListIterator implements the Iterator interface and contains extra functionality, such as adding an element, replacing an element, getting the index position for previous and next elements, etc. What is difference between fail-fast and fail-safe? The Iterator's fail-safe property works with the clone of the underlying collection and thus, it is not affected by any modification in the collection. All the collection classes in java. Fail-fast iterators throw a ConcurrentModificationException , while fail-safe iterator never throws such an exception. How HashMap works in Java?
- A HashMap in Java stores key-value pairs. The HashMap requires a hash function and uses hashCode and equals methods, in order to put and retrieve elements to and from the collection respectively. When the put method is invoked, the HashMap calculates the hash value of the key and stores the pair in the appropriate index inside the collection. If the key exists, its value is updated with the new value. Some important characteristics of a HashMap are its capacity, its load factor and the threshold resizing.
Common Java Collections Interview Questions (With Example Answers)
What is the importance of hashCode and equals methods? A HashMap in Java uses the hashCode and equals methods to determine the index of the key-value pair. These methods are also used when we request the value of a specific key. If these methods are not implemented correctly, two different keys might produce the same hash value and thus, will be considered as equal by the collection. Furthermore, these methods are also used to detect duplicates. Thus, the implementation of both methods is crucial to the accuracy and correctness of the HashMap. What differences exist between HashMap and Hashtable? Both the HashMap and Hashtable classes implement the Map interface and thus, have very similar characteristics.Top 50 Java Collections Interview Questions You Need To Know
A Hashtable is synchronized, while a HashMap is not. Thus, HashMap is preferred in single-threaded environments, while a Hashtable is suitable for multi-threaded environments. A HashMap provides its set of keys and a Java application can iterate over them. Thus, a HashMap is fail-fast. On the other hand, a Hashtable provides an Enumeration of its keys.[2021 Updated] Top 50 Java Collections Interview Questions And Answers
The Hashtable class is considered to be a legacy class. What is difference between Array and ArrayList? When will you use Array over ArrayList? The Array and ArrayList classes differ on the following features: Arrays can contain primitive or objects, while an ArrayList can contain only objects. Arrays have fixed size, while an ArrayList is dynamic. An ArrayList provides more methods and features, such as addAll, removeAll, iterator, etc. For a list of primitive data types, the collections use autoboxing to reduce the coding effort. However, this approach makes them slower when working on fixed size primitive data types. What is difference between ArrayList and LinkedList?- Both the ArrayList and LinkedList classes implement the List interface, but they differ on the following features: An ArrayList is an index based data structure backed by an Array. It provides random access to its elements with a performance equal to O 1. On the other hand, a LinkedList stores its data as list of elements and every element is linked to its previous and next element. In this case, the search operation for an element has execution time equal to O n. The Insertion, addition and removal operations of an element are faster in a LinkedList compared to an ArrayList , because there is no need of resizing an array or updating the index when an element is added in some arbitrary position inside the collection. A LinkedList consumes more memory than an ArrayList , because every node in a LinkedList stores two references, one for its previous element and one for its next element.
- Check also our article ArrayList vs. What is Comparable and Comparator interface? List their differences. Java provides the Comparable interface, which contains only one method, called compareTo. This method compares two objects, in order to impose an order between them. Specifically, it returns a negative integer, zero, or a positive integer to indicate that the input object is less than, equal or greater than the existing object. Java provides the Comparator interface, which contains two methods, called compare and equals. The first method compares its two input arguments and imposes an order between them. It returns a negative integer, zero, or a positive integer to indicate that the first argument is less than, equal to, or greater than the second.
- The second method requires an object as a parameter and aims to decide whether the input object is equal to the comparator. The method returns true, only if the specified object is also a comparator and it imposes the same ordering as the comparator. What is Java Priority Queue? The PriorityQueue is an unbounded queue, based on a priority heap and its elements are ordered in their natural order. At the time of its creation, we can provide a Comparator that is responsible for ordering the elements of the PriorityQueue. Finally, the Java PriorityQueue is not thread-safe and it requires O log n time for its enqueing and dequeing operations. What do you know about the big-O notation and can you give some examples with respect to different data structures?
- The Big-O notation simply describes how well an algorithm scales or performs in the worst case scenario as the number of elements in a data structure increases. The Big-O notation can also be used to describe other behavior such as memory consumption. Since the collection classes are actually data structures, we usually use the Big-O notation to chose the best implementation to use, based on time, memory and performance.
- Big-O notation can give a good indication about performance for large amounts of data. What is the tradeoff between using an unordered array versus an ordered array? The major advantage of an ordered array is that the search times have time complexity of O log n , compared to that of an unordered array, which is O n. The disadvantage of an ordered array is that the insertion operation has a time complexity of O n , because the elements with higher values must be moved to make room for the new element.
Top 10 Java Collections Interview Questions Answers For Beginners | Java67
Instead, the insertion operation for an unordered array takes constant time of O 1. What are some of the best practices relating to the Java Collection framework? For example if the size of the elements is fixed and know a priori, we shall use an Array , instead of an ArrayList. Some collection classes allow us to specify their initial capacity. Thus, if we have an estimation on the number of elements that will be stored, we can use it to avoid rehashing or resizing. Always use Generics for type-safety, readability, and robustness.- Also, by using Generics you avoid the ClassCastException during runtime. Use immutable classes provided by the Java Development Kit JDK as a key in a Map, in order to avoid the implementation of the hashCode and equals methods for our custom class. Program in terms of interface not implementation. Return zero-length collections or arrays as opposed to returning a null in case the underlying collection is actually empty. Enumeration is twice as fast as compared to an Iterator and uses very less memory. However, the Iterator is much safer compared to Enumeration , because other threads are not able to modify the collection object that is currently traversed by the iterator.
- Also, Iterators allow the caller to remove elements from the underlying collection, something which is not possible with Enumeration. What is the difference between HashSet and TreeSet? The HashSet is Implemented using a hash table and thus, its elements are not ordered. The add, remove, and contains methods of a HashSet have constant time complexity O 1.
- On the other hand, a TreeSet is implemented using a tree structure. The elements in a TreeSet are sorted, and thus, the add, remove, and contains methods have time complexity of O logn.
- It is true that every interview is different as per the different job profiles. Here, we have prepared the important Java Collection Interview Questions and Answers which will help you get success in your interview. Java Collection framework is one of the key chapters for learning core java properly. Java Collection holding a lot of interfaces and classes which are under java.
The 100 Frequently Asked Java Interview Questions And Answers
All those interfaces and classes have huge utilization in any java based application. Java has introduced a different version in almost last couple of years. Collection framework is always a highlighted package for Java, so every version of Java always came with some key features specifically on the Collection framework. Please explain what are the new features came with the collection framework for Java 8 version? Answer: Java 8 version already came with some of the key or major changes in Java Collection Framework, features are explaining below: Stream API for Java: for supporting some of the sequential and parallel processing. Introducing the for Each method specifically for iterator interface: This is one of the default methods when the developer is going to use an iterator for fetching data from any of the collection interfaces.- Java 8 introduced one of the key features called Lambda expressions because of its arguments, it will be very easy to use on the iterator interface. Miscellaneous Collection API: a lot of methods have been introduced in the case of Miscellaneous Collection of the framework. Methods are for Each Remaining, replace all, computer, merge specially introduce in Iterator interface. Explain in detail about the Java Collection framework using in Java application. Provide more details on exact benefits provided by collection framework in Java application? Answer: Collection framework is kind of a much-highlighted package from the day java introduce this package. Initially, it only holding some of the legacy interfaces, like Vector, Hashtable, Stack, and Array, which are obsolete in terms of the longtime journey of java. From java upper version introducing lot of interfaces which very much feature-oriented and come with some key role for any kind of java programming. Implementation and define the algorithm for those interfaces are really useful for any Java developer any time of execution.
Top 50 Java Collections Interview Questions And Answers | Edureka
Java Collection has worked with these approaches long days and came with a lot of concurrent collection class for ensuring thread safety on varieties operations. Benefits of collection framework defined below: Reduced development efforts by implementing defined collection classes. Code quality is always enhanced including performance. Efforts on code maintenance always been reduced.- Improve code reusability and maintained proper interoperability. Let us move to the next Java Collection Interview Questions. Explain details benefits available in case of using collection framework generic version from the starting of collection interfaces and classes on Java 4 version onwards? Answer: Java 1. It introduced some of the approaches which actually provided ClassCastException at compilation time. Initially, the same exception came at runtime without any previous definition. But in the case of compilation, it will never be identified. Now if the developer mentioned one collection interface object type, then it will never able to accept any other object reference.
Java Garbage Collection Interview Questions And Answers - Flipboard
If by mistake developers have done the same, then it will throw ClasCastExpection at compilation time. There have a lot of interfaces already defined in case of collection framework design of existing java application. Please explain in detail about some of the popular key interfaces available in collection framework, explain their utility of using? Answer: Some of the key interfaces are defined below which are available for Collection framework: Collection: It is one of the root interfaces of the entire collection hierarchy.- It actually holding group of available objects from the development point of view called Elements. Normally any kind of direct implementation of this Collection interface is not available for the Java platform. Set: This is one of the key collection interfaces which extends Collection interface and ensure of not containing any duplicate elements. List: It is one of the ordered collection which extending Collection interface and accepting duplicate elements, which are one of the key difference between set and list. Map: Map is also an interface which holding data with the key-value pair. It never contains any duplicate key values. Whether the collection frame can able to extend two very key interfaces in Java core packages, one is cloneable and another one is Serializable? Please explain some details explanation of your answer to the above concern?
- Answer: Cloning and serializing on collection interface is not possible at all, as collection interface can have multiple interfaces and there have some possibilities of getting duplicate values or unique values on those specific interfaces. So clone or serialize will not possible on that. But there has some specific method defined for some common interface which may use own clone method to do this. In Collection Framework, one of the key interface very frequently used by the developer called Map. But surprisingly Map interface not extend Collection framework directly. Can you please explain the same why it not extended? Answer: The map interface is one of the key interfaces of collection framework, but it never extends Collection interface as Map always maintained data as a key-value pair, which never ensures of storing multiple elements, which represents one of the key features of Collection framework. One of the important interface which is very frequently used in collection framework which iterator.
- Please explain when it can be useful and what the exact utility of it is? Answer: The iterator is one of the popular interfaces for iterating the data available in any active collection. Every collection has one specific method name iterator, which returns the reference of an Iterator object. Then two of the key methods hasNext and Next ensuring of fetching the last row and using the same. Two key interfaces in the collection framework for reading data from the collection and using it are Iterator and Enumerator. Please explain in detail what can be the difference between both the looping approaches available in the collection framework? Answer: Enumeration is one the key iterating feature especially using for legacy classes.
ArrayList, HashMap And Collection Interview Questions Answers In Java | Java Prorgram Examples
It always much faster than the normal iterator interface. But Iterator is always more secure to use as it ensuring thread safety of the iterated collection object. Every interface of the collection framework contains one specific method call add for adding some components value in the interface. But in the case of Iterator interface there does not have any kind of add method, can you explain why it not in there? Answer: Iterator interface mainly used for iterating on the data holding by any active collection. It will never add any kind of elements and never able to provide some guaranty on the order of iteration. Explain the difference between two key interfaces of the collection framework, Iterator, and ListIterator? Answer: Iterator and Listiterator both are using for iterating collection data and help the developer for working with multiple elements of the collection.
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