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| Core java - Interview Questions and Answers for 'Time' - 17 question(s) found - Order By Newest | |||||||||||
 Very frequently asked. Among first few questions in almost all interviews. Among Top 5 frequently asked questions. Frequently asked in Indian service companies (HCL,TCS,Infosys,Capgemini etc based on multiple feedback ) and Epam Systems | |||||||||||
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| Ans. "equals" is the method of object class which is supposed to be overridden to check object equality, whereas "==" operator evaluate to see if the object handlers on the left and right are pointing to the same object in memory. x.equals(y) means the references x and y are holding objects that are equal. x==y means that the references x and y have same object. Sample code: String x = new String("str"); String y = new String("str"); System.out.println(x == y); // prints false System.out.println(x.equals(y)); // prints true | |||||||||||
 Sample Code for equals | |||||||||||
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 Discuss Correct / Improve  java string comparison string object class == equals object equality operator == vs equals equals vs ==  Asked in 294 Companies  basic  frequent | |||||||||||
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| Ans. OOPs or Object Oriented Programming is a Programming model which is organized around Objects instead of processes. Instead of a process calling series of processes, this model stresses on communication between objects. Objects that all self sustained, provide security by encapsulating it's members and providing abstracted interfaces over the functions it performs. OOP's facilitate the following features 1. Inheritance for Code Reuse 2. Abstraction for modularity, maintenance and agility 3. Encapsulation for security and protection 4. Polymorphism for flexibility and interfacing | |||||||||||
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| Discuss Correct / Improve oops oops features Asked in 260 Companies basic frequent | |||||||||||
| Basic and Very Frequently asked. | |||||||||||
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| Ans. Polymorphism means the condition of occurring in several different forms. Polymorphism in Java is achieved in two manners 1. Static polymorphism is the polymorphic resolution identified at compile time and is achieved through function overloading whereas 2. Dynamic polymorphism is the polymorphic resolution identified at runtime and is achieved through method overriding. | |||||||||||
| Sample Code for overloading Sample Code for overriding | |||||||||||
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| Discuss Correct / Improve polymorphism object oriented programming (oops) oops concepts oops concepts Asked in 108 Companies Basic frequent | |||||||||||
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| Ans. 1. Overriding method can not be more restrictive than the overridden method. reason : in case of polymorphism , at object creation jvm look for actual runtime object. jvm does not look for reference type and while calling methods it look for overridden method. If by means subclass were allowed to change the access modifier on the overriding method, then suddenly at runtime when the JVM invokes the true objects version of the method rather than the reference types version then it will be problematic 2. In case of subclass and superclass define in different package, we can override only those method which have public or protected access. 3. We can not override any private method because private methods can not be inherited and if method can not be inherited then method can not be overridden. | |||||||||||
| Sample Code for Overriding | |||||||||||
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| Discuss Correct / Improve java overriding access specifier inheritence oops polymorphism object oriented programming (oops) oops concepts runtime polymorphism object oriented programming (oops) oops concepts Asked in 4 Companies | |||||||||||
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| Ans. Java uses Just-In-Time compiler to enable high performance. Just-In-Time compiler is a program that turns Java bytecode into instructions that can be sent directly to the processor. | |||||||||||
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| Discuss Correct / Improve java compiler jvm bytecode justintime compiler architecture | |||||||||||
| Usually asked to entry level software developers. | |||||||||||
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| Ans. public static void main(String[] args) { int num1 = 1; int num2 = 2; num1 = num1^num2; num2 = num1^num2; num1 = num1^num2; System.out.print("num1 = " + num1 +", num2 = "+num2); } | |||||||||||
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| Discuss Correct / Improve code coding Asked in 37 Companies basic frequent | |||||||||||
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| Ans. Yes, we can do that. Compiler wont complain. But using object reference we can only access methods which have been defined for object class i.e clone(), equals(), hashCode(), toString() etc. We cannot access methods defined in String class or in any class in hierarchy between String and Object. For example - we cannot do obj.append("abc") as it will now give compile time error. | |||||||||||
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| Discuss Correct / Improve object initialization object declaration runtime polymorphism object oriented programming (oops) oops concepts | |||||||||||
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| Ans. The Exception class has two main subclasses : IOException class and RuntimeException Class. | |||||||||||
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| Discuss Correct / Improve java exceptions exception class ioexception runtimeexception | |||||||||||
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| Ans. To avoid ClassCastException. Though the following code will compile fine but will result in ClassCastException during runtime. Fruit fruit = new Apple(); Banana banana = Banana(fruit); // ClassCastException This code will not give compile time error as Banana and Fruit are related as Banana either extends or implement Fruit, So downcasting is acceptable. With this code we assume that the Fruit handler will have the Apple object at that point, violating which the code will throw the exception. This exception can be avoided by following code. Fruit fruit = new Apple(); if(fruit instanceOf Banana){ Banana banana = Banana(fruit); // ClassCastException } | |||||||||||
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| Discuss Correct / Improve java instanceof classcastexception runtime exceptions instanceOf operator | |||||||||||
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| Ans. hh= hours in 1-12 format HH= hours in 0-23 format kk = Hours in 1-24 format KK= hours in 0-11 format | |||||||||||
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| Discuss Correct / Improve Date Date Time Format Date Time | |||||||||||
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| Ans. dynamic method dispatch is a process in which a call to an overridden method is resolved at runtime rather than at compile-time. This is used to achieve runtime polymorphism in java. | |||||||||||
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| Discuss Correct / Improve overriding runtime polymorphism object oriented programming (oops) oops concepts | |||||||||||
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| Ans. Dynamic dispatch in java is also known as runtime polymorphism.It is a process in which a call to an overriden method is resolved at runtime. | |||||||||||
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| Discuss Correct / Improve dynamic dispatch runtime polymorphism object oriented programming (oops) oops concepts | |||||||||||
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| This question was recently asked at 'Intime Tec'.This question is still unanswered. Can you please provide an answer. | |||||||||||
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| Ans. Yes, Runtime Polymprohism requires either Class inheritance or Interface implementation. | |||||||||||
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| Discuss Correct / Improve runtime polymorphism object oriented programming (oops) oops concepts method overriding inheritance object oriented programming (oops) oops concepts | |||||||||||
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| Discuss Correct / Improve vtable virtual method table method overriding runtime polymorphism object oriented programming (oops) oops concepts | |||||||||||
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| Discuss Correct / Improve virtual method table method overriding runtime polymorphism object oriented programming (oops) oops concepts expert rare | |||||||||||
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| Ans. There is one VTable for each class. | |||||||||||
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| Discuss Correct / Improve virtual table method vtable runtime polymorphism object oriented programming (oops) oops concepts method overriding intermediate rare | |||||||||||
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Which of the following statement is not true ?
