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Core Java - Interview Questions and Answers for 'Classe' - 68 question(s) found - Order By Rating | ||||
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Ans. data under collection are actually stored in memory so that they can be retrieved when needed whereas data in streams are not stored and hence we need to construct it again when needed. | ||||
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Like Discuss Correct / Improve  collection classes  stream api  collection vs stream Asked in 1 Companies | ||||
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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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Like Discuss Correct / Improve  arraylist  arrays  collection classes  collections basic   frequent | ||||
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Like Discuss Correct / Improve  concurrent collection classes   fail fast   fail-fast  collections  collection classes expert | ||||
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Ans. Yes, With Java 8 we can use Interfaces as collection of utility methods through the use of default methods. | ||||
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Like Discuss Correct / Improve  java 8  interfaces  utility class   utility classes | ||||
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Ans. Stack Properties Vector BlockingQueue ConcurrentMap ConcurrentNavigableMap | ||||
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Like Discuss Correct / Improve  collections  concurrent classes | ||||
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Ans. Immutable objects are thread-safe so you will not have any synchronization issues.Immutable objects are good for Map keys and Set elements, since these typically do not change once created.Immutability makes it easier to write, use and reason about the code (class invariant is established once and then unchanged)Immutability makes it easier to parallelize your program as there are no conflicts among objects.The internal state of your program will be consistent even if you have exceptions.References to immutable objects can be cached as they are not going to change. | ||||
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Like Discuss Correct / Improve  immutable  immutability classes   benefits of immutable  immutability classes Asked in 1 Companies | ||||
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Ans. string and wrapper class objects | ||||
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Like Discuss Correct / Improve  immutability  immutable  immutability classes   immutable  immutability collections Asked in 3 Companies | ||||
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Ans. There is no concept of de referencing with primitive types and hence they are implicitly immutable. Having wrapper classes as mutable offers disadvantages compared to primitive types. Wrapper classes being immutable offer similar advantage as primitive types.It actually overshadows the disadvantage wrapper class could have if they are immutable. | ||||
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Like Discuss Correct / Improve  immutable  immutability classes  wrapper classes | ||||
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Ans. No, As collection classes involve use of Generics, they cannot accept primitive types. | ||||
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Like Discuss Correct / Improve  collection classes  collections | ||||
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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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Like Discuss Correct / Improve  static class  inner classes   nested classes Expert   rare | ||||
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Ans. Abstract Classes provide default implementations of methods that are inherited by the classes that extend them, which was not the case for Interfaces. This changed in Java 8, where default implementations are provided for methods. | ||||
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Ans. Yes | ||||
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Like Discuss Correct / Improve  wrapper classes  immutable  immutability | ||||
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Ans. Yes , we can have an interface that is part of a class. | ||||
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Like Discuss Correct / Improve  inner classes   inner interface  nested classes | ||||
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Ans. Yes that's legal in java | ||||
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Like Discuss Correct / Improve  inner classes  nested classes  sub class Basic | ||||
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Ans. Yes that can be done public class OuterClass { public class InnerClass extends OuterClass { } } | ||||
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Like Discuss Correct / Improve  inner classes  nested classes  sub class Basic | ||||
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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. By encapsulating it within another class and declaring it private. In such a case, it will only be accessible through parent class or parent class object. | ||||
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Like Discuss Correct / Improve  private class   private inner class  class hiding  encapsulation  object oriented programming (oops)  oops concepts  inner classes   nested classes | ||||
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Ans. We can declare an inner class as private and hence would be restricting it's access from outside. We cannot make outer class as private. | ||||
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Like Discuss Correct / Improve  private class   inner classes  nested classes | ||||
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Ans. Boxing conversion converts expressions of primitive type to corresponding expressions of reference type. For example boolean to Boolean long to Long double to Double | ||||
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Like Discuss Correct / Improve  data type  boxing  wrapper classes | ||||
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Ans. Classes having only static methods in java is called util classes. As they don't have specific object state, they are basically intend to have shared code and state through static elements and methods. They save resources by sharing code. | ||||
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Like Discuss Correct / Improve  util classes | ||||
Try 1 Question(s) Test | ||||
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Ans. OuterClass.class AND OuterClass$InnerClass.class | ||||
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Like Discuss Correct / Improve  class files  compilation  compile  inner classes   nested classes | ||||
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Ans. It depends on the type of inner class To access non static inner class method new OuterClass().new InnerClass().getMethod(); To access static method of static inner class new OuterClass.InnerClass().getMethod(); | ||||
Sample Code for inner class | ||||
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Like Discuss Correct / Improve  inner classes  nested aclasses Asked in 1 Companies Intermediate   frequent | ||||
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Ans. Abstract classes provide a mechanism of interfacing ( using abstract method ) as well as inheritance ( extending abstract class ). So they should be used in place of interfaces in case there is some code ( methods ) or object body ( member elements ) that can be reused with inheritance. | ||||
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Like Discuss Correct / Improve  abstract classes Asked in 1 Companies | ||||
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Ans. Collections in java is a framework of classes that provides an abstracted data structure to store and manipulate the group of objects. Each class is unique in the way it stores , search , sort and modify the elements. | ||||
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Like Discuss Correct / Improve  collections  collection classes Asked in 1 Companies Basic   frequent | ||||
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Ans. Yes, we can define an inner class within interface.Inside the interface, the inner class is implicitly public static. So the following is legit in Java public interface BuggyBreadInterface { void doSomething(); public class BuggyBreadClass implements BuggyBreadInterface{ void doSomething(){ System.out.println("Do something"); } } } | ||||
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Ans. The simplest way is to ignore them if Maven enforcer plugin is complaining about it but it may lead to runtime problems later. We can do the dependency:tree to see from where these duplicate ones are coming and hence can exclude the duplicate one. | ||||
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Like Discuss Correct / Improve  maven   ban duplicate classes enforcer plugin | ||||
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Ans. Yes , we have been using this plugin with our projects and its purpose is to warn and stop the Build if there are duplicates of the same package and class are being carried either directly or through transitive dependencies. the duplicate could be coming through different types of dependencies or through different versions of the same dependency. Its purpose is to make sure that there is only one copy thats being used at compile time and runtime and hence shouldnt later result in runtime problems. | ||||
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Ans. No, If both Parent and Derived are outer classes. public class Vehicle { private static String manufacturingDate = "2016"; } public class Car extends Vehicle{ public static void main(String args[]){ System.out.println(manufacturingDate); // error - The field Vehicle.manufacturingDate is not visible } } Yes, If derived is the inner class of Parent. public class Vehicle { private static String manufacturingDate = "2016"; static public class Car extends Vehicle{ public static void main(String args[]){ System.out.println(manufacturingDate); // no problem } } } | ||||
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Like Discuss Correct / Improve  private members   private methods   private variables   inheritance  object oriented programming (oops)  oops concepts   members visibility   inner classes  nexted classes basic   frequent | ||||
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Ans. In first case we are trying to initialize Inner class object using the instance of Outer Class whereas in second case we are trying to initialize the Inner class object directly using the Outer class name. In second case , Inner class is "static inner class" as we cannot access "non static inner class" using Classname alone. In first case, the inner class could be either "static inner class" or "non static inner class". | ||||
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Like Discuss Correct / Improve  inner classes  inner class   static inner class   new operator | ||||