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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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 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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| 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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| 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. 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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| 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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| 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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| 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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Discuss Correct / Improve aws route53  Asked in 1 Companies | ||||
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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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| Discuss Correct / Improve aws vpc aws subnet subnet vpc Amazon Web Services (AWS) | ||||
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| Ans. A cookie is a small piece of text stored on a user's computer by the browser for a specific domain. Commonly used for authentication, storing site preferences, and server session identification. | ||||
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Discuss Correct / Improve cookie javascript web application session management browser j2ee Asked in 16 Companies  basic  frequent | ||||
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| Ans. Simple Inner Class, Local Inner Class, Anonymous Inner Class, Static Nested Inner Class. | ||||
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| 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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| Discuss Correct / Improve java collections list set map list vs set vs map Asked in 8 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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| 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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| 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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| Discuss Correct / Improve java oops static static variable memory intermediate | ||||
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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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| 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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| Discuss Correct / Improve java collections hashmap map hashtable yes-no Asked in 1 Companies | ||||
| 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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| 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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| 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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| Discuss Correct / Improve character coding ascii unicode utf | ||||
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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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| Discuss Correct / Improve java oops constructor inheritence Asked in 1 Companies expert rare | ||||
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| Ans. Web server. | ||||
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| Discuss Correct / Improve apache web server j2ee | ||||
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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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| Discuss Correct / Improve java oops abstract classes Abstract vs Concrete Class Asked in 1 Companies basic frequent | ||||
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| Ans. Vectors are synchronized whereas Array lists are not. | ||||
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| Discuss Correct / Improve java basic interview question vector arraylist collections synchronization vector vs arraylist Asked in 35 Companies basic frequent | ||||
| 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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| Discuss Correct / Improve java oops immutable immutability immutable immutability class string class basic interview question Asked in 18 Companies Basic frequent | ||||
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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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| Discuss Correct / Improve java oops constructor object instantiation | ||||
| Frequently asked to fresh graduates and less experienced. | ||||
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| Ans. Inheritance. | ||||
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| Discuss Correct / Improve inheritance object oriented programming (oops) oops concepts java oops composition object oriented programming (oops) oops concepts Asked in 1 Companies basic frequent | ||||
| Very frequently asked in phone and walk in interviews. | ||||
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| Ans. An interface without any method declaration is called as marker interface. there are 3 in-built interfaces in JVM i.e. serializable, clonable, remote | ||||
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| Discuss Correct / Improve java oops interfaces marker interface serializable clonable Asked in 21 Companies intermediate frequent | ||||
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| Frequently asked to fresh graduates. | ||||
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| Ans. Process is a program in execution whereas thread is a separate path of execution in a program. | ||||
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| Discuss Correct / Improve java threads multi threading operating system process vs thread Asked in 24 Companies basic frequent | ||||
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| Ans. Autoboxing is the automatic conversion that the Java compiler makes between the primitive types and their corresponding object wrapper classes | ||||
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| Discuss Correct / Improve java java5 autoboxing wrapper classes Asked in 2 Companies basic frequent | ||||
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Which of the following is not type of inner classes ?
