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Ans. Inner Class is a class that is nested within another class whereas sub class is a class that extends or inherit another class. Inner class can only be accessed using reference of outer class ( Class name , if inner class is static or object reference, if inner class is non static ) whereas Sub class is accessed directly. In terms of memory, inner class is stored just like another class having it's own body whereas sub class carries the body of parent class as well as it's own fields in memory. | ||||
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Like Discuss Correct / Improve  inner classes  nested classes  inner class vs sub class  nested class vs sub class Basic | ||||
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Ans. In Breadth first algorithm, all the adjacent nodes of the starting node is visited first and then the same rule is followed while moving inwards whereas In Depth first algorithm, all the nodes of a single traversal path are visited first till a cycle or an end is found. For example , given the following entries of adjacent nodes 1,2 1,3 1,6 2,4 2,5 3,6 The Breadth first path would be 1,2,3,6,4,5 and Depth first path would be 1,2,4,5,3,6 | ||||
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Like Discuss Correct / Improve  graph traversal  breadth first vs depth first   frequent | ||||
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Ans. No. It will result in a type mismatch error. Collection<Collection> collection = new LinkedList<Collection>(); is a valid initialization as collection being reference of "Collection" class can hold object of derived Class "LinkedList" due to runtime Polymorphism. Runtime polymorphism is not applicable to type arguments. | ||||
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Like Discuss Correct / Improve  generics  type argument | ||||
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Ans. With Collection classes , we cannot use primitive types. Moreover for any class using generic types, we cannot use primitive types. They add more functionality by means of additional methods. As their reference can be null , they offer consistent check for uninitialized state. They facilitate caching and reuse by means of constant Pools. | ||||
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Like Discuss Correct / Improve  wrapper classes  benefits of wrapper classes over primitives | ||||
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Ans. We are not resizing the first array here but assigning the reference strArray to a new Array with size 5. So after line 2, We have 2 arrays in memory, one with size 2 and other with size 5 with strArray referring to second array with size 5. | ||||
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Like Discuss Correct / Improve  arrays  array initialization | ||||
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Ans. CloudFront for Static Media and cached content EC2 and EKS ( Docker ) for main application computing RDS and DynamoDB for Database Lambda ( computing ) for running back end cron jobs Kinesis for streaming and SQS for queuing CloudWatch for Monitoring CloudFormation for Infrastructure templating S3 for Object Storage | ||||
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Ans. A Region is a Geographical entity like US-East , US-West etc. Each Region may have multiple availability zones where each zone comprise of 1 or more Data Center located with each other. Edge Locations are the sites that hosts cached content for faster delivery and for saving network traffic as they feed content from sites that are local or near to consumption. | ||||
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Like Discuss Correct / Improve  aws region  aws availability zone  aws edge location  region vs availabillity zone | ||||
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Ans. S3 Standard S3 IA - Infrequently Accessed S3 One Zone IA - One Zone only , Infrequently Accessed S3 Glacier - achieved S3 Standard is most expensive , Glacier is least expensive | ||||
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Like Discuss Correct / Improve  aws s3  aws storage  amazon cloud storage  amazon s3 | ||||
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Ans. Storage Tier ( IA , Standard , Glacier etc ) Storage ( Volume of Data ) No of Requests Meta Data Data Transfer Speed acceleration through cache and Edge Location | ||||
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Like Discuss Correct / Improve  aws s3  aws storage  amazon cloud storage  amazon s3 | ||||
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Ans. EC2 - Time and Reservation , Instance Type ( Memory , Computation power ) S3 - Accessibility Frequency , Data Transfer , Storage Space CloudFront - Geography, No of Locations EBS - IOPS, Access Frequency | ||||
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Like Discuss Correct / Improve  aws ec2  aws computing  amazon cloud computing  amazon ec2  aws s3  aws storage  amazon cloud storage  amazon s3  aws cloudfront  amazon cloudfront  aws ebs | ||||
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Ans. Simple Weighted Latency Failover GeoLocation Multivalue | ||||
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Ans. A VPC is devided into multiple subnets. Subnet in a particular VPC could be public or private. For Example - A particular account may have multiple vpc's for each of the business type. For each Business or VPC , One can have different subnets to cater to each department so that access across departments could be restricted. But still there could be identities that have control over different subnets. Moreover we could have multiple subnets for each department so as to have distinguished public and private networks having different types of applications ( public facing or internal consumption ) | ||||
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Like Discuss Correct / Improve  aws vpc  aws subnet  subnet  vpc  Amazon Web Services (AWS) | ||||
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Ans. Simple Inner Class, Local Inner Class, Anonymous Inner Class, Static Nested Inner Class. | ||||
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Like Discuss Correct / Improve  java   inner classes   classes Asked in 6 Companies basic   frequent | ||||
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Frequently asked in Indian Service Companies. Tech Mahindra ( Based on 3 inputs ) and Infosys ( 3 inputs ) | ||||
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Ans. List - Members are stored in sequence in memory and can be accessed through index. Set - There is no relevance of sequence and index. Sets doesn't contain duplicates whereas multiset can have duplicates. Map - Contains Key , Value pairs. | ||||
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Like Discuss Correct / Improve  java   collections   list   set   map   list vs set vs map Asked in 8 Companies basic   frequent | ||||
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Ans. Java doesn't support multiple inheritance. Interfaces does't facilitate inheritance and hence implementation of multiple interfaces doesn't make multiple inheritance. | ||||
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Like Discuss Correct / Improve  java   oop   oop concepts   inheritence   multiple inheritence   basic interview question Asked in 10 Companies basic   frequent | ||||
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Frequently asked at HCL Technologies ( Based on 3 feedback ) | ||||
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Ans. Checked exceptions are the exceptions for which compiler throws an errors if they are not checked whereas unchecked exceptions are caught during run time only and hence can't be checked. | ||||
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Like Discuss Correct / Improve  java   exceptions   checked exceptions   unchecked exceptions   exception handling   checked vs unchecked exceptions Asked in 39 Companies basic   frequent | ||||
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Very frequently asked. Favorite question in Walk in Drive of many Indian service companies. | ||||
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Ans. Final variable is a variable constant that cannot be changed after initialization. | ||||
Sample Code for final variable | ||||
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Like Discuss Correct / Improve  oops   java   final   final variable   basic interview question Asked in 12 Companies basic   frequent | ||||
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Ans. They are loaded at runtime when the respective Class is loaded. | ||||
Sample Code for static variable | ||||
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Ans. No. Only Object and its members are serialized. Static variables are shared variables and doesn't correspond to a specific object. | ||||
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Like Discuss Correct / Improve  serialization   java   oops   static   static variables Asked in 1 Companies intermediate   rare | ||||
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Ans. Yes , for HashMap. HashMap implements Map interface. HashMap allows one null key and any number of null values. | ||||
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Usually asked only to fresh graduates. | ||||
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Ans. In preemptive scheduling, highest priority task continues execution till it enters a not running state or a higher priority task comes into existence. In time slicing, the task continues its execution for a predefined period of time and reenters the pool of ready tasks. | ||||
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Like Discuss Correct / Improve  operating system   scheduling   threads   multi threading   rare | ||||
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Ans. One should make sure that all the included objects are also serializable. If any of the objects is not serializable then it throws a NotSerializable Exception. | ||||
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Like Discuss Correct / Improve  serialization   java   oops   object expert | ||||
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Ans. Unicode requires 16 bits and ASCII require 7 bits. Although the ASCII character set uses only 7 bits, it is usually represented as 8 bits. UTF-8 represents characters using 8, 16, and 18 bit patterns. UTF-16 uses 16-bit and larger bit patterns. | ||||
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Ans. You cannot inherit a constructor. That is, you cannot create a instance of a subclass using a constructor of one of it's superclasses. One of the main reasons is because you probably don't want to override the superclasses constructor, which would be possible if they were inherited. By giving the developer the ability to override a superclasses constructor you would erode the encapsulation abilities of the language. | ||||
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Ans. Web server. | ||||
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Ans. Abstract classes are only meant to be sub classed and not meant to be instantiated whereas concrete classes are meant to be instantiated. | ||||
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Ans. Vectors are synchronized whereas Array lists are not. | ||||
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Ans. It in Java is used to indicate that a field should not be serialized. | ||||
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Like Discuss Correct / Improve  java   oops   serialization   transient   java keywords Asked in 39 Companies intermediate   frequent | ||||
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Very Frequently asked. Usually asked along with String Class related questions. | ||||
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Ans. Class using which only immutable (objects that cannot be changed after initialization) objects can be created. | ||||
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Ans. Though It's often confused with each other, Object Creation ( Instantiation ) and Initialization ( Construction ) are different things in Java. Construction follows object creation. Object Creation is the process to create the object in memory and returning its handler. Java provides New keyword for object creation. Initialization is the process of setting the initial / default values to the members. Constructor is used for this purpose. If we don't provide any constructor, Java provides one default implementation to set the default values according to the member data types. | ||||
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Like Discuss Correct / Improve  java   oops   constructor   object instantiation | ||||