|Hypertext Markup LanguageCascading Style SheetsExtensible Markup LanguageJava ScriptjQueryAngularJSOracle SQLOracle PL/SQLOracle D2K FormsOracle D2K ReportsOracle DatabaseJavaJava Database ConnectivityJava ServletJava Server PagesHibernateApache TomcatCC++PHPMy-SqlUnix/LinuxMS-DOSHR Interviews|
|What is Overriding?|
|When a class defines a method using the same name, return type, and arguments as a method in its superclass, the method in the class overrides the method in the superclass. When the method is invoked for an object of the class, it is the new definition of the method that is called, and not the method definition from superclass. Methods may be overridden to be more public, not more private.|
|What are different types of inner classes?|
Nested top-level classes, Member classes, Local classes, Anonymous classes
Nested top-level classes- If you declare a class within a class and specify the static modifier, the compiler treats the class just like any other top-level class.
Member classes - Member inner classes are just like other member methods and member variables and access to the member class is restricted, just like methods and variables. This means a public member class acts similarly to a nested top-level class. The primary difference between member classes and nested top-level classes is that member classes have access to the specific instance of the enclosing class.
Local classes - Local classes are like local variables, specific to a block of code. Their visibility is only within the block of their declaration. In order for the class to be useful beyond the declaration block, it would need to implement a more publicly available interface.Because local classes are not members, the modifiers public, protected, private, and static are not usable.
Anonymous classes - Anonymous inner classes extend local inner classes one level further. As anonymous classes have no name, you cannot provide a constructor
|Are the imports checked for validity at compile time? e.g. will the code containing an import such as java.lang.ABCD compile?|
|Yes the imports are checked for the semantic validity at compile time. The code containing above line of import will not compile. It will throw an error saying,can not resolve symbol symbol: class ABCD location: package io import java.io.ABCD;|
|Does importing a package imports the subpackages as well? e.g. Does importing com.MyTest.* also import com.MyTest.UnitTests.*?|
|No you will have to import the subpackages explicitly. Importing com.MyTest.* will import classes in the package MyTest only. It will not import any class in any of it's subpackage.|
|What is the difference between declaring a variable and defining a variable?|
|In declaration we just mention the type of the variable and it's name. We do not initialize it. But defining means declaration + initialization. e.g String s; is just a declaration while String s = new String ('abcd'); Or String s = 'abcd'; are both definitions.|
|What is the default value of an object reference declared as an instance variable?|
|null unless we define it explicitly.|
|Can a level class be private or protected?|
|No. A level class can not be private or protected. It can have either 'public' or no modifier. If it does not have a modifier it is supposed to have a default access.If a level class is declared as private the compiler will complain that the 'modifier private is not allowed here'. This means that a level class can not be private. Same is the case with protected.|
|What type of parameter passing does Java support?|
|In Java the arguments are always passed by value .|
|Primitive data types are passed by reference or pass by value?|
|Primitive data types are passed by value.|
|Objects are passed by value or by reference?|
|Java only supports pass by value. With objects, the object reference itself is passed by value and so both the original reference and parameter copy both refer to the same object .|
|What is serialization?|
|Serialization is a mechanism by which you can save the state of an object by converting it to a byte stream.|
|How do I serialize an object to a file?|
|The class whose instances are to be serialized should implement an interface Serializable. Then you pass the instance to the ObjectOutputStream which is connected to a fileoutputstream. This will save the object to a file.|
|Which methods of Serializable interface should I implement?|
|The serializable interface is an empty interface, it does not contain any methods. So we do not implement any methods.|
|How can I customize the seralization process? i.e. how can one have a control over the serialization process?|
|Yes it is possible to have control over serialization process. The class should implement Externalizable interface. This interface contains two methods namely readExternal and writeExternal. You should implement these methods and write the logic for customizing the serialization process.|
|What is the common usage of serialization?|
|Whenever an object is to be sent over the network, objects need to be serialized. Moreover if the state of an object is to be saved, objects need to be serilazed.|
|What is Externalizable interface?|
|Externalizable is an interface which contains two methods readExternal and writeExternal. These methods give you a control over the serialization mechanism. Thus if your class implements this interface, you can customize the serialization process by implementing these methods.|
|When you serialize an object, what happens to the object references included in the object?|
|The serialization mechanism generates an object graph for serialization. Thus it determines whether the included object references are serializable or not. This is a recursive process. Thus when an object is serialized, all the included objects are also serialized alongwith the original obect.|
|What one should take care of while serializing the object?|
|One should make sure that all the included objects are also serializable. If any of the objects is not serializable then it throws a NotSerializableException.|
|What happens to the static fields of a class during serialization?|
|There are three exceptions in which serialization doesnot necessarily read and write to the stream. These are 1. Serialization ignores static fields, because they are not part of ay particular state state. 2. Base class fields are only hendled if the base class itself is serializable. 3. Transient fields.|
|Does Java provide any construct to find out the size of an object?|
|No there is not sizeof operator in Java. So there is not direct way to determine the size of an object directly in Java.|
|Give a simplest way to find out the time a method takes for execution without using any profiling tool?|
|Read the system time just before the method is invoked and immediately after method returns. Take the time difference, which will give you the time taken by a method for execution. To put it in code... long start = System.currentTimeMillis (); method (); long end = System.currentTimeMillis (); System.out.println ('Time taken for execution is ' + (end - start)); Remember that if the time taken for execution is too small, it might show that it is taking zero milliseconds for execution. Try it on a method which is big enough, in the sense the one which is doing considerable amout of processing.|
|What are wrapper classes?|
|Java provides specialized classes corresponding to each of the primitive data types. These are called wrapper classes. They are e.g. Integer, Character, Double etc.|
|Why do we need wrapper classes?|
|It is sometimes easier to deal with primitives as objects. Moreover most of the collection classes store objects and not primitive data types. And also the wrapper classes provide many utility methods also. Because of these resons we need wrapper classes. And since we create instances of these classes we can store them in any of the collection classes and pass them around as a collection. Also we can pass them around as method parameters where a method expects an object.|
|What are checked exceptions?|
|Checked exception are those which the Java compiler forces you to catch. e.g. IOException are checked Exceptions.|
|What are runtime exceptions?|
|Runtime exceptions are those exceptions that are thrown at runtime because of either wrong input data or because of wrong business logic etc. These are not checked by the compiler at compile time.|
|Pipes and Cistern|
Two pipes A and B can fill a tank in 6 hours and 4 hours respectively. If they are opened on alternate hours and if pipe A s opened first, in how many hours, the tank shall be full?
A large tanker can be filled by two pipes A and B in 60 min and 40 min respectively. How many minutes will it take to fill the tanker from empty state if B is used for first half of the time, and A and B fill it together for the other half?
A tank is filled by 3 pipes with uniform flow. The first two pipes operating simultaneously fill the tank in the same time during which the tank is filled by the third pipe alone. The 2nd pipe fills the tank 5 hours faster than first pipe and 4 hours slower than third pipe. The time required by first pipe is?
Two pipes A and B together can fill a cistern in 4 hours. Had they been opened separately, then B would have taken 6 hours more than A to fill the cistern. How much time will be taken by A to fill the cistern separately?
Two pipes A and B can fill a tank in 24 min and 32 min respectively. If both the pipes are opened simultaneously, after how much time B should be closed so that the tank is full in 18 min?
Two pipes A and B can fill a tank in 36 min and 45 min respectively. A water pipe C can empty the tank in 30 min. First A and B are opened. after 7 min, C is also opened. In how much time, the tank is full?
Two pipes can fill a cistern in 14 hours and 16 hours respectively. The pipes are opened simultaneously and it is found that due to leakage in the bottom it took 32 min more to fill the cistern. When the cistern is full, in what time will the leak empty it?
Bucket P has thrice the capacity as Bucket Q. It takes 60 turns for Bucket P to fill the empty drum. How many turns it will take for both the buckets P and Q, having each turn together to fill the empty drum?
In a class , 30 % of the students offered English, 20 % offered Hindi and 10 % offered Both.If a student is offered at random, what is the probability that he has offered English or Hindi?
In a lottery ,there are 10 prizes and 25 blanks.A lottery is drawn at random. what is the probability of getting a prize ?
Two dice are thrown simultaneously .what is the probability of getting two numbers whose product is even?
Two diced are tossed the probability that the total score is a prime number?
Two cards are drawn at random from a pack of 52 cards What is the probability that either both are black or both are queens?
Two dice are thrown together .What is the probability that the sum of the number on the two faces is divisible by 4 or 6?
A bag contains 6 white and 4 black balls .Two balls are drawn at random .Find the probability that they are of the same colour?
In a simultaneous throw of a pair of dice,find the probability of getting a total more than 7?
An unbiased die is tossed.Find the probability of getting a multiple of 3?
|Problems on Ages|
My brother is 3 years elder to me. My father was 28 years of age when my sister was born while my mother was 26 years of age when i was born. If my sister was 4 years of age when my brother was born,then what was the age my father and mother respectively when my brother was born?
बैंकिंग कार्मिक चयन संस्थान Institute of Banking Personnel Selection(IBPS) - 7855 पद - 29/07/2022 अंतिम तिथि
कर्मचारी चयन आयोग (एसएससी) Staff Selection Commission (SSC) - 1411 पद - 29/07/2022 अंतिम तिथि
|Jobs in Rajasthan|
राजस्थान अधीनस्थ और मंत्रिस्तरीय सेवा चयन बोर्ड Rajasthan Subordinate and Ministerial Services Selection Board (RSMSSB) - 5546 पद - 22-Jul-2022 अंतिम तिथि
उत्तर मध्य रेलवे भर्ती प्रकोष्ठ Railway Recruitment Cell(NCR) - 1659 पद - 01/08/2022 अंतिम तिथि
|Jobs in West Bengal|
इंडियन पोस्ट सर्विस Indian Post Service - 2357 पद - 19/08/2021 अंतिम तिथि - पश्चिम बंगाल पोस्टल सर्कल
भारतीय स्टेट बैंक State Bank of India(SBI) - 6100 पद - 26/07/2021 अंतिम तिथि - CRPD/APPR/2021-22/10
कर्मचारी चयन आयोग Staff Selection Commission(SSC) - 25271 पद - 31/08/2021 अंतिम तिथि
|Jobs in Madhya Pradesh|
राष्ट्रीय स्वास्थ्य मिशन मध्य प्रदेश National Health Mission MP(NRHM) - 5215 पद - 22/06/2021 अंतिम तिथि
|Jobs in Punjab|
पंजाब स्टेट पावर कॉर्पोरेशन लिमिटेड Punjab State Power Corporation Limited (PSPCL) - 2632 पद - 20/06/2021 अंतिम तिथि
|Jobs in Chhattisgarh|
स्वास्थ्य सेवा निदेशालय, छत्तीसगढ़ Department of Health & Family Welfare, Chhattisgarh - 267 पद - 26/06/2021 अंतिम तिथि