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Interview Questions and Answers - Order By Newest | ||||
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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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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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Like Discuss Correct / Improve  java   oops   abstract classes   Abstract vs Concrete Class Asked in 1 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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Like Discuss Correct / Improve  java   java5   autoboxing   wrapper classes Asked in 2 Companies basic   frequent | ||||
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Ans. Collections can only hold objects, It can't hold primitive data types. Collections have performance overheads as they deal with objects and offer dynamic memory expansion. This dynamic expansion could be a bigger overhead if the collection class needs consecutive memory location like Vectors. Collections doesn't allow modification while traversal as it may lead to concurrentModificationException. | ||||
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Like Discuss Correct / Improve  java   collections   collections classes   disadvantages of collections over arrays   collections vs arrays | ||||
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Ans. It could be worthy to move a method to util class if the method needs to be shared, doesn't require polymorphic behavior and need not be overridden in special cases. Don't belong to one group through is-a relationship ( You can share through parent class method ) Don't implement a specific interface ( java 8 default methods ) Doesn't involve complex computing as you will be loosing the benefit of object state with just static method. Doesn't require polymorphic behavior as static methods don't participate in runtime polymorphism. | ||||
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Like Discuss Correct / Improve  utility classes   util classes   static methods   application design   rare | ||||
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Ans. For top level class we can only use "public" and "default". We can use private with inner class. | ||||
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Like Discuss Correct / Improve  java   class   access specifier   inner classes basic   frequent | ||||
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Ans. boolean is a primitive type whereas Boolean is a class. | ||||
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Ans. A wrapper class is any class which "wraps" or "encapsulates" the functionality of another class or component. A Wrapper Class that wraps or encapsulates the primitive data type is called Primitive Wrapper Class. | ||||
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Ans. Adapter. | ||||
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Ans. Inner class is a type of nested class. Inner classes are non static nested classes i.e the one that are associated with the instance of outer class. | ||||
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Ans. Any interface declared inside a class or an interface. It is static by default. | ||||
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Like Discuss Correct / Improve  java   oops   nested classes | ||||
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Ans. Keep it as a Abstract Class if its a "Is a" Relationsship and should do subset/all of the functionality. Keep it as Interface if its a "Should Do" relationship. | ||||
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Like Discuss Correct / Improve  java   oops   abstract classes   interfaces   advanced Asked in 3 Companies | ||||
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Ans. Collections are re-sizable in nature. We can increase or decrease the size as per recruitment. Collections can hold both homogeneous and heterogeneous data's. Every collection follows some standard data structures. Collection provides many useful built in methods for traversing,sorting and search. | ||||
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Like Discuss Correct / Improve  java   collections   collections classes   advantages of collections over arrays   collections vs arrays   basic interview question Asked in 6 Companies basic   frequent | ||||
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Ans. 1. Entity classes should have default constructor. 2. Entity classes should be declared non final. 3. All elements to be persisted should be declared private and should have public getters and setters in the Java Bean style. 4. All classes should have an ID that maps to Primary Key for the table. | ||||
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Like Discuss Correct / Improve  hibernate   entity classes hibernate | ||||
Ans. Constructors , Classes ( Outer ) , Interfaces , Local variables , Inner Class methods and instance variables. | ||||
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Like Discuss Correct / Improve  oops   java   static   nested classes   static nested classes | ||||
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Ans. Sometime we just need classes or class objects just to be used as part of a particular class or objects. Making them non nested won't make any difference as far as functionality is concerner but making them Nested provide a level of convenience and protection fro, being used anywhere else. Moreover it helps reducing the Code. | ||||
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Ans. You can put related classes together as a single logical group. Nested classes can access all class members of the enclosing class, which might be useful in certain cases. Nested classes are sometimes useful for specific purposes. For example, anonymous inner classes are useful for writing simpler event-handling code with AWT/Swing. | ||||
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Like Discuss Correct / Improve  java   nested classes   inner classes   oops   classes | ||||
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Ans. The accessibility (public, protected, etc.) of the static nested class is defined by the outer class. A static nested class is not an inner class, it's a top-level nested class. The name of the static nested class is expressed with OuterClassName.NestedClassName syntax. When you define an inner nested class (or interface) inside an interface, the nested class is declared implicitly public and static. Static nested classes can be declared abstract or final. Static nested classes can extend another class or it can be used as a base class. Static nested classes can have static members. Static nested classes can access the members of the outer class (only static members, obviously). The outer class can also access the members (even private members) of the nested class through an object of nested class. If you don't declare an instance of the nested class, the outer class cannot access nested class elements directly. | ||||
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Like Discuss Correct / Improve  java   oops   nested classes   static nested classes   inner classes | ||||
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Ans. The accessibility (public, protected, etc.) of the inner class is defined by the outer class. Just like top-level classes, an inner class can extend a class or can implement interfaces. Similarly, an inner class can be extended by other classes, and an inner interface can be implemented or extended by other classes or interfaces. An inner class can be declared final or abstract.Inner classes can have inner classes, but you will have a hard time reading or understanding such complex nesting of classes. | ||||
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Ans. You can create a non-static local class inside a body of code. Interfaces cannot have local classes, and you cannot create local interfaces. Local classes are accessible only from the body of the code in which the class is defined. The local classes are completely inaccessible outside the body of the code in which the class is defined. You can extend a class or implement interfaces while defining a local class. A local class can access all the variables available in the body of the code in which it is defined. You can pass only final variables to a local inner class. | ||||
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Like Discuss Correct / Improve  java   oops   inner classes   local classes   classes   method local inner classes Asked in 1 Companies | ||||
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Ans. Anonymous classes are defined in the new expression itself, so you cannot create multiple objects of an anonymous class. You cannot explicitly extend a class or explicitly implement interfaces when defining an anonymous class. An anonymous inner class is always created as part of a statement; don't forget to close the statement after the class definition with a curly brace. This is a rare case in Java, a curly brace followed by a semicolon. Anonymous inner classes have no name, and their type must be either a subclass of the named type or an implementer of the named interface | ||||
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Ans. Yes for the Wrapper class Integer but not for the primitive int. | ||||
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Ans. Yes but as Hibernate creates the Proxy Classes inherited from the Entity Classes to communicate with Database for lazy initialization. Declaring entity classes as final will prohibit communication with database lazily and hence will be a performance hit. | ||||
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Ans. It will throw the ParseException as the date format doesn't abide with the format of the specified date. | ||||
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Like Discuss Correct / Improve  date   utility classes   dateformat   exception   parseexception | ||||
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Ans. Yes. Long wrapper class has overloaded constructor which takes String as input and then translate it to the long value and stored it as long. | ||||
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Ans. No. This will give a compilation error saying "Abstract methods do not specify a body". | ||||
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Ans. Yes, but there can be only 1 public class in a single file. | ||||
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Like Discuss Correct / Improve  java   classes | ||||
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Ans. Method Nested Static Inner Class | ||||
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Must know at all levels. Among Top 10 frequently asked questions in Java. Very frequently asked to fresh graduates or less experienced professionals. | ||||
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Ans. Its a facility for code reuse and independent extension wherein a derived class inherits the properties of parent class. | ||||
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Like Discuss Correct / Improve  inheritance  object oriented programming (oops)  oops concepts  oops concepts  java concepts  code reuse  code re-use   classes  derived classes Asked in 14 Companies basic   frequent | ||||
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Ans. A Java bean is a class which abides by following conventions: Core of the object is member elements and not operations ( methods ) Member Elements can be accessed by getters (and setters if those properties are not read-only). serializable. | ||||
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