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Q2731. Does abstract class have public constructor?

Core Java

Ans. Yes, an abstract class can have a constructor in Java.

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Q2732. What measures would you take to avoid Java threading issues in a multi-threaded environment ?

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Q2733. Can we use Param Store with AWS Lambda ?

Amazon Web Services (AWS)

Ans. Yes

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Q2734. Is HashMap Synchronized ?

Core Java

Ans. No HashMap isn't synchronized. ConcurrentHashMap and Hashtable are synchronized.

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Q2735. Is ConcurrentHashMap synchronized ?

Core Java

Ans. Yes, ConcurrentHashMap is synchronized.

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Q2736. Difference between equals and compareTo in Java ?

Core Java

Ans. "equals" is the method of object class which is supposed to be overridden to check object equality. x.equals(y) means the references x and y are holding objects that are equal.

The compareTo() method is used for comparing two objects in Java. It is usually defined for the classes whose objects needs to be ordered through Comparable interface or need to be part of an ordered collection like TreeSet or TreeMap.

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Q2737. Difference between equals and hashcode in java ?

Core Java

Ans. "equals" is the method of object class which is supposed to be overridden to check object equality. x.equals(y) means the references x and y are holding objects that are equal with the equality defined by the definition of equals method.

Hashcode is used for bucketing in Hash implementations like HashMap, HashTable, HashSet etc. The value received from hashcode() is used as bucket number for storing elements. This bucket number is the address of the element inside the set/map. when you do contains() then it will take the hashcode of the element, then look for the bucket where hashcode points to and if more than 1 element is found in the same bucket (multiple objects can have the same hashcode) then it uses the equals() method to evaluate if object are equal, and then decide if contain() is true or false, or decide if element could be added in the set or not.

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Q2738. Difference between equals and equalsignorecase in Java ?

Core Java

Ans. "equals" method is the method of object class that needs to be overridden to check object equality. This is not specific to any class like String.

equalsignorecase is the method of String class that provides a definition that ignores the case of characters during comparison.

The only difference between them in String class is that the equals() methods considers the case while equalsIgnoreCase() methods ignores the case during comparison.

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Q2739. Why is String a class in Java ?

Core Java

Ans. 1. Creating a class helps in specifying operations on the Strings like length , sub string , concatenation etc.

2. It acts as a Wrapper class for "Array of Characters" and hence facilitates it's usage in collections, assignment to null.

3. Immutability of String objects facilitates in reuse , security and caching.

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Q2740. Difference between composition and aggregation in java ?

Core Java

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Q2741. Does garbage collection affects performance of the application ?

Core Java

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Q2742. Does garbage collection happens in String pool ?

Core Java

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Q2743. Does garbage collection call dispose ?

Core Java

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Q2744. What is the difference between final and constant in java ?

Amazon Web Services (AWS)

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Q2745. What is the difference between final and static in java ?

Core Java

Ans. final keyword is used to restrict the user from modifying the variable, extending the class and overriding a method

static keyword is used for memory management which can be used for variable, class, method where in it belongs to the class not to the instance of object

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Q2746. How can we run a java program through command line ?

Core Java

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Q2747. Difference between ArrayList and Vector ?

Core Java

Ans. Vector is Synchronized one where as Arraylist is not Synchronized.

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Q2748. difference between ArrayList and array ?

Core Java

Ans. ArrayList is a variable length collection class whereas arrays are fixed length primitive structure.

We can use generics with arraylist but not with arrays.

We can store primitive data types within arrays but can't with ArrayList. In ArrayList that needs to be converted to Wrapper objects.

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Q2749. Difference between ArrayList and HashSet ?

Core Java

Ans. ArrayList is a list , i.e an implementation of List interface whereas HashSet is a Set and an implementation of Set interface.

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Q2750. Difference between TreeMap and SortedMap ?

Core Java

Ans. sortedMap is an interface ,while TreeMap is an implementation of sortMap.

We can not create an instance of sortedMap but we can create an instance of treeMap

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Q2751. Difference between HashMap and Dictionary in Java ?

Core Java

Ans. HashMap implements the Map interface while the Dictionary does not.

HashMap was introduced after HashTable and Dictionary.

Dictionary is currently obsolete in java.

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Q2752. Difference between System.getEnv and System.getProperties ?

Core Java

Ans. System.getEnv gets the environment variables where System.getProperties gets Java properties.

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Q2753. Can we load environment variables into Properties in Java ? How ?

Core Java

Ans. Yes

new Properties().putAll(System.getenv());

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Q2754. What is xssf and hssf ?

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Q2755. Can we have two interfaces having method with same name and arguments?

Core Java

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Q2756. If you are asked to test an application without any documentation, What type of testing will you do ?

Testing

Ans. White Box Testing
Unit Testing
Ad Hoc Testing

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Q2757. how hashmap work? Write a program that uses map interface ?

Core Java

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Q2758. Sort an Employee Object based on Name or Age

Database

Ans. Use Comparable or Comparator interface

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Q2759. What is cluster ?

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Q2760. What is the concept of hibernate versioning ?

Hibernate

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