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 Q2251. When you will synchronize a piece of your code?
Ans. When you expect your code will be accessed by different threads and these threads may change a particular data causing data corruption.

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   Like         Discuss         Correct / Improve     java   threads   multi threading   synchronization   concurrency      basic        frequent

 Q2252. What is an applet? What is the lifecycle of an applet?
Ans. Applet is a dynamic and interactive program that runs inside a web page displayed by a java capable browser.

Lifecycle methods of Applet -

init( ) method - Can be called when an applet is first loaded
start( ) method - Can be called each time an applet is started
paint( ) method - Can be called when the applet is minimized or maximized
stop( ) method - Can be used when the browser moves off the applet's page
destroy( ) method - Can be called when the browser is finished with the applet

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   Like         Discuss         Correct / Improve     java   java ui   applet   swing   awt   lifecycle of applet   technologies

 Q2253. What is meant by controls and what are different types of controls in AWT / SWT?
Ans. Controls are components that allow a user to interact with your application and SWT / AWT supports the following types of controls:

Labels, Push Buttons, Check Boxes, Choice Lists, Lists, Scrollbars, Text Components.

These controls are subclasses of Component.

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   Like         Discuss         Correct / Improve     java   java ui   swt   awt   types of controls

 Q2254. What is a stream and what are the types of Streams and classes of the Streams?Core Java
Ans. A Stream is an abstraction that either produces or consumes information. There are two types of Streams :

Byte Streams: Provide a convenient means for handling input and output of bytes.

Character Streams: Provide a convenient means for handling input & output of characters.

Byte Streams classes: Are defined by using two abstract classes, namely InputStream and OutputStream.

Character Streams classes: Are defined by using two abstract classes, namely Reader and Writer.

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   Like         Discuss         Correct / Improve     java   file io   streams   byte stream   character stream  file handling     Asked in 3 Companies

 Q2255. What is session tracking and how do you track a user session in servlets?Java EE
Ans. Session tracking is a mechanism that servlets use to maintain state about a series requests from the same user across some period of time. The methods used for session tracking are:

User Authentication - occurs when a web server restricts access to some of its resources to only those clients that log in using a recognized username and password

Hidden form fields - fields are added to an HTML form that are not displayed in the client's browser. When the form containing the fields is submitted, the fields are sent back to the server

URL rewriting - every URL that the user clicks on is dynamically modified or rewritten to include extra information. The extra information can be in the form of extra path information, added parameters or some custom, server-specific URL change.

Cookies - a bit of information that is sent by a web server to a browser and which can later be read back from that browser.

HttpSession- places a limit on the number of sessions that can exist in memory.

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   Like         Discuss         Correct / Improve     j2ee   servlets   session   session management   web applications   cookies   httpsession   url rewriting   architecture     Asked in 1 Companies

 Q2256. What is connection pooling?Database
Ans. It's a technique to allow multiple clients to make use of a cached set of shared and reusable connection objects providing access to a database or other resource.

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  Q2257. Advantage of Collection classes over Arrays ?Core Java
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

 Q2258. What are the Disadvantages of using Collection Classes over Arrays ?Core Java
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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 Q2259. Can we call constructor explicitly ?
Ans. Yes.

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 Q2260. Does a class inherit the constructor of its super class?
Ans. No.

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 Q2261. What is the difference between float and double?
Ans. Float can represent up to 7 digits accurately after decimal point, where as double can represent up to 15 digits accurately after decimal point.

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 Q2262. What is the difference between System.out ,System.err and System.in?
Ans. System.out and System.err both represent the monitor by default and hence can be used to send data or results to the monitor. But System.out is used to display normal messages and results whereas System.err is used to display error messages and System.in represents InputStream object, which by default represents standard input device, i.e., keyboard.

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   Like         Discuss         Correct / Improve     java   io   system.out   system.err   system.in   difference between   advanced   basic interview question

 Q2263. Is it possible to compile and run a Java program without writing main( ) method?
Ans. Yes, it is possible by using a static block in the Java program.

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Frequently asked in Infosys and HCL Technologies ( Based on 2 feedback )
 Q2264. What are different ways of object creation in Java ?Core Java
Ans. Using new operator - new xyzClass()

Using factory methods - xyzFactory.getInstance( )

Using newInstance( ) method - (Class.forName(xyzClass))emp.newInstance( )

By cloning an already available object - (xyzClass)obj1.clone( )

  Sample Code for object initialization using clone

  Sample Code for object initialization using getInstance

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 Q2265. What is Generalization and Specialization in terms of casting ?Core Java
Ans. Generalization or UpCasting is a phenomenon where a sub class is prompted to a super class, and hence becomes more general. Generalization needs widening or up-casting. Specialization or DownCasting is a phenomenon where a super class is narrowed down to a sub class. Specialization needs narrowing or down-casting.

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 Q2266. Can we call the garbage collector explicitly ?Core Java
Ans. Yes, We can call garbage collector directly but it doesn't guarantees that the gc will start executing immediately. This gc( ) method appears in both Runtime and System classes of java.lang package.

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Advanced level question usually asked to senior developers , leads and architects.
 Q2267. How does volatile affect code optimization by compiler?Core Java
Ans. Volatile is an instruction that the variables can be accessed by multiple threads and hence shouldn't be cached. As volatile variables are never cached and hence their retrieval cannot be optimized.

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 Q2268. Do you think that Java should have had pointers ?Core Java
Ans. Open ended Questions.

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 Q2269. How would you go about debugging a NullPointerException?Core Java
Ans. Open ended Questions.

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 Q2270. Should good code be self-documenting, or is it the responsibility of the developer to document it?Process
Ans. Open ended Questions.

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   Like         Discuss         Correct / Improve     java   open questions   code review   documentation   clean code

 Q2271. What are points to consider in terms of access modifier when we are overriding any method?Core Java
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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 Q2272. what is covariant return type? Core Java
Ans. co-variant return type states that return type of overriding method can be subtype of the return type declared in method of superclass. it has been introduced since jdk 1.5

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 Q2273. How compiler handles the exceptions in overriding ?Core Java
Ans. 1)The overriding methods can throw any runtime Exception , here in the case of runtime exception overriding method (subclass method) should not worry about exception being thrown by superclass method.

2)If superclass method does not throw any exception then while overriding, the subclass method can not throw any new checked exception but it can throw any runtime exception

3) Different exceptions in java follow some hierarchy tree(inheritance). In this case , if superclass method throws any checked exception , then while overriding the method in subclass we can not throw any new checked exception or any checked exception which are higher in hierarchy than the exception thrown in superclass method

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 Q2274. Why is Java considered Portable Language ?Core Java
Ans. Java is a portable-language because without any modification we can use Java byte-code in any platform(which supports Java). So this byte-code is portable and we can use in any other major platforms.

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 Q2275. Tell something about history of Java ?Core Java
Ans. Java was initially found in 1991 by James Gosling, Sun Micro Systems. At first it was called as "Oak". In 1995 then it was later renamed to "Java". java is a originally a platform independent language. Currently Oracle, America owns Java.

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 Q2276. How to find if JVM is 32 or 64 bit from Java program. ?
Core Java
Ans. You can find JVM - 32 bit or 64 bit by using System.getProperty() from Java program.

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 Q2277. Does every class needs to have one non parameterized constructor ?Core Java
Ans. No. Every Class only needs to have one constructor - With parameters or without parameters. Compiler provides a default non parameterized constructor if no constructors is defined.

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   Like         Discuss         Correct / Improve     java   oops   constructor   default constructor   yes no      intermediate
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 Q2278. Difference between throw and throws ?Core Java
Ans. throw is used to explicitly throw an exception especially custom exceptions, whereas throws is used to declare that the method can throw an exception.

We cannot throw multiple exceptions using throw statement but we can declare that a method can throw multiple exceptions using throws and comma separator.

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 Q2279. Can we use "this" within static method ? Why ?Core Java
Ans. No. Even though "this" would mean a reference to current object id the method gets called using object reference but "this" would mean an ambiguity if the same static method gets called using Class name.

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 Q2280. Similarity and Difference between static block and static method ?Core Java
Ans. Both belong to the class as a whole and not to the individual objects. Static methods are explicitly called for execution whereas Static block gets executed when the Class gets loaded by the JVM.

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