The document discusses 20 important Java programming interview questions. It covers topics such as the differences between interfaces and abstract classes, when to use abstract classes versus interfaces, what the Serializable interface does, how to force garbage collection, the differences between StringBuffer and StringBuilder, checked and unchecked exceptions, how Java allocates stack and heap memory, Java reflection, the Java Virtual Machine, the differences between JDK and JRE, and more.
Basic java important interview questions and answers to secure a jobGaruda Trainings
P2Cinfotech is one of the leading, Online IT Training facilities and Job Consultant, spread all over the world. We have successfully conducted online classes on various Software Technologies that are currently in Demand. To name a few, we provide quality online training for QA, QTP, Manual Testing, HP LoadRunner, BA, Java Technologies, SEO, Web Technologies, .NET, Oracle DBA etc.
TOPS Technologies Leading IT Training Institute offer training in Php, .Net, Java, iPhone, Android, Software testing and SEO. By TOPS Technologies. http://www.tops-int.com
Top 30 Java Phone Interview Questions Answers for Freshers, 1 to 2 Years Expe...SynergisticMedia
In this Java interview questions blog, you will find the most asked questions and answers for Java interviews. Practicing these questions will help crack the interview. So, let's get started.
Core Java Tutorial. In case you want to get trained in Spring Framework you can refer here:
<a href="https://www.emexotechnologies.com/courses/java-development-training/core-java-training/">Java Training</a>
Basic java important interview questions and answers to secure a jobGaruda Trainings
P2Cinfotech is one of the leading, Online IT Training facilities and Job Consultant, spread all over the world. We have successfully conducted online classes on various Software Technologies that are currently in Demand. To name a few, we provide quality online training for QA, QTP, Manual Testing, HP LoadRunner, BA, Java Technologies, SEO, Web Technologies, .NET, Oracle DBA etc.
TOPS Technologies Leading IT Training Institute offer training in Php, .Net, Java, iPhone, Android, Software testing and SEO. By TOPS Technologies. http://www.tops-int.com
Top 30 Java Phone Interview Questions Answers for Freshers, 1 to 2 Years Expe...SynergisticMedia
In this Java interview questions blog, you will find the most asked questions and answers for Java interviews. Practicing these questions will help crack the interview. So, let's get started.
Core Java Tutorial. In case you want to get trained in Spring Framework you can refer here:
<a href="https://www.emexotechnologies.com/courses/java-development-training/core-java-training/">Java Training</a>
Java Tutorial For Beginners - Step By Step | Java Basics | Java Certification...Edureka!
** Java Certification Training: https://www.edureka.co/java-j2ee-soa-... **
This Edureka PPT on “Java Tutorial For Beginners” will give you a brief insight about Java and its various fundamental concepts along with their practical implementation. Through this tutorial, you will learn the following topics:
1. Introduction to Java
2. JVM vs JRE vs JDK
3. Java Fundamentals
4. Objects & Classes
5. Methods & Access Modifiers
6. Flow Of Control
7. Java Arrays
In this core java training session, you will learn Elements of Java programming. Topics covered in this session are:
• Quick review of some important concepts from last class
• History of Java
• JDK and JRE
• Byte Code and JVM (Java Virtual Machine)
• Platform Independence
• Principles of Object Oriented Programming
• Writing your first Java Application
• Elements of Java programming language
• Built in Data Types
• Conditional Statements
• Loops
For more information about this course visit on this link: https://www.mindsmapped.com/courses/software-development/learn-java-fundamentals-hands-on-training-on-core-java-concepts/
This keyword is a reference variable that refer the current object in java.
This keyword can be used for call current class constructor.
http://www.tutorial4us.com/java/java-this-keyword
Gives You the brief idea about packages in JAVA
By N.V.Raja Sekhar Reddy
www.technolamp.co.in
Want more interesting...
Watch and Like us @ https://www.facebook.com/Technolamp.co.in
subscribe videos @ http://www.youtube.com/user/nvrajasekhar
Introduction to Java Programming, Basic Structure, variables Data type, input...Mr. Akaash
This is First Lecture of java Programming which cover all basic points (ie. History and feature of java, Introduction to java, about variables data type and compilation....
Java Tutorial For Beginners - Step By Step | Java Basics | Java Certification...Edureka!
** Java Certification Training: https://www.edureka.co/java-j2ee-soa-... **
This Edureka PPT on “Java Tutorial For Beginners” will give you a brief insight about Java and its various fundamental concepts along with their practical implementation. Through this tutorial, you will learn the following topics:
1. Introduction to Java
2. JVM vs JRE vs JDK
3. Java Fundamentals
4. Objects & Classes
5. Methods & Access Modifiers
6. Flow Of Control
7. Java Arrays
In this core java training session, you will learn Elements of Java programming. Topics covered in this session are:
• Quick review of some important concepts from last class
• History of Java
• JDK and JRE
• Byte Code and JVM (Java Virtual Machine)
• Platform Independence
• Principles of Object Oriented Programming
• Writing your first Java Application
• Elements of Java programming language
• Built in Data Types
• Conditional Statements
• Loops
For more information about this course visit on this link: https://www.mindsmapped.com/courses/software-development/learn-java-fundamentals-hands-on-training-on-core-java-concepts/
This keyword is a reference variable that refer the current object in java.
This keyword can be used for call current class constructor.
http://www.tutorial4us.com/java/java-this-keyword
Gives You the brief idea about packages in JAVA
By N.V.Raja Sekhar Reddy
www.technolamp.co.in
Want more interesting...
Watch and Like us @ https://www.facebook.com/Technolamp.co.in
subscribe videos @ http://www.youtube.com/user/nvrajasekhar
Introduction to Java Programming, Basic Structure, variables Data type, input...Mr. Akaash
This is First Lecture of java Programming which cover all basic points (ie. History and feature of java, Introduction to java, about variables data type and compilation....
Лекция для сотрудников фирмы Soft-logic, проведенная 13.11.2014. В ходе лекции рассматривались следующие ключевые моменты:
1. Назначение lambda-выражений
2. Синтаксис lambda-выражений
3. Функциональные интерфейсы
4. Default и статические методы в интерфейсах
5. Ссылки на методы
6. Область действия переменных
7. Трансляция lambda-выражений
8. Сериализация lambda-выражений
JDK.IO 2016 (http://jdk.io)
Java EE 7 introduced a new batch processing API. This session will go over how to use the batch processing API introduced with Java EE 7. This API is makes it easy to implement long running data/compute intensive jobs which need to be scheduled or initiated on-demand. Basics of the API will be demonstrated via code samples. The API will also be compared to Spring Batching and Hadoop to provide context and guidance on when these technologies are appropriate.
These questions are prepared by Classical Programming Experts and are asked during job interviews.The Solution to the given programs are prepared by Programming Experts and are often asked in job interviews. Knowing solution to these problems will help you clear your concepts.
Top 50 java ee 7 best practices [con5669]Ryan Cuprak
JavaOne 2016
This session provides 50 best practices for Java EE 7, with examples. The best practices covered focus primarily on JPA, CDI, JAX-WS, and JAX-RS. In addition, topics involving testing and deployment are covered. This presentation points out where best practices have changed, common misconceptions, and antipatterns that should be avoided. This is a fast-paced presentation with many code samples.
Do you want to crack android interview?
These are the most frequently asked Android Interview questions for experienced and entry level android programmers.
These question are the basic questions for Interview based on Java language. These questions are able to crack the interview based on java language
Learn more at blog : --
https://solutionbyexpert.blogspot.com/2020/08/become-expert-secret-of-success-ii.html
#coding
#coding development skill program
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Some of the common interview questions asked during a Java Interview. These may apply to Java Interviews. Be prepared with answers for the interview questions below when you prepare for an interview. Also have an example to explain how you worked on various interview questions asked below. Java Developers are expected to have references and be able to explain from their past experiences. All the Best for a successful career as a Java Developer!
Some of the common interview questions asked during a Java Interview. These may apply to Java Interviews. Be prepared with answers for the interview questions below when you prepare for an interview. Also have an example to explain how you worked on various interview questions asked below. Java Developers are expected to have references and be able to explain from their past experiences. All the Best for a successful career as a Java Developer!
Read| The latest issue of The Challenger is here! We are thrilled to announce that our school paper has qualified for the NATIONAL SCHOOLS PRESS CONFERENCE (NSPC) 2024. Thank you for your unwavering support and trust. Dive into the stories that made us stand out!
Unit 8 - Information and Communication Technology (Paper I).pdfThiyagu K
This slides describes the basic concepts of ICT, basics of Email, Emerging Technology and Digital Initiatives in Education. This presentations aligns with the UGC Paper I syllabus.
Biological screening of herbal drugs: Introduction and Need for
Phyto-Pharmacological Screening, New Strategies for evaluating
Natural Products, In vitro evaluation techniques for Antioxidants, Antimicrobial and Anticancer drugs. In vivo evaluation techniques
for Anti-inflammatory, Antiulcer, Anticancer, Wound healing, Antidiabetic, Hepatoprotective, Cardio protective, Diuretics and
Antifertility, Toxicity studies as per OECD guidelines
June 3, 2024 Anti-Semitism Letter Sent to MIT President Kornbluth and MIT Cor...Levi Shapiro
Letter from the Congress of the United States regarding Anti-Semitism sent June 3rd to MIT President Sally Kornbluth, MIT Corp Chair, Mark Gorenberg
Dear Dr. Kornbluth and Mr. Gorenberg,
The US House of Representatives is deeply concerned by ongoing and pervasive acts of antisemitic
harassment and intimidation at the Massachusetts Institute of Technology (MIT). Failing to act decisively to ensure a safe learning environment for all students would be a grave dereliction of your responsibilities as President of MIT and Chair of the MIT Corporation.
This Congress will not stand idly by and allow an environment hostile to Jewish students to persist. The House believes that your institution is in violation of Title VI of the Civil Rights Act, and the inability or
unwillingness to rectify this violation through action requires accountability.
Postsecondary education is a unique opportunity for students to learn and have their ideas and beliefs challenged. However, universities receiving hundreds of millions of federal funds annually have denied
students that opportunity and have been hijacked to become venues for the promotion of terrorism, antisemitic harassment and intimidation, unlawful encampments, and in some cases, assaults and riots.
The House of Representatives will not countenance the use of federal funds to indoctrinate students into hateful, antisemitic, anti-American supporters of terrorism. Investigations into campus antisemitism by the Committee on Education and the Workforce and the Committee on Ways and Means have been expanded into a Congress-wide probe across all relevant jurisdictions to address this national crisis. The undersigned Committees will conduct oversight into the use of federal funds at MIT and its learning environment under authorities granted to each Committee.
• The Committee on Education and the Workforce has been investigating your institution since December 7, 2023. The Committee has broad jurisdiction over postsecondary education, including its compliance with Title VI of the Civil Rights Act, campus safety concerns over disruptions to the learning environment, and the awarding of federal student aid under the Higher Education Act.
• The Committee on Oversight and Accountability is investigating the sources of funding and other support flowing to groups espousing pro-Hamas propaganda and engaged in antisemitic harassment and intimidation of students. The Committee on Oversight and Accountability is the principal oversight committee of the US House of Representatives and has broad authority to investigate “any matter” at “any time” under House Rule X.
• The Committee on Ways and Means has been investigating several universities since November 15, 2023, when the Committee held a hearing entitled From Ivory Towers to Dark Corners: Investigating the Nexus Between Antisemitism, Tax-Exempt Universities, and Terror Financing. The Committee followed the hearing with letters to those institutions on January 10, 202
2024.06.01 Introducing a competency framework for languag learning materials ...Sandy Millin
http://sandymillin.wordpress.com/iateflwebinar2024
Published classroom materials form the basis of syllabuses, drive teacher professional development, and have a potentially huge influence on learners, teachers and education systems. All teachers also create their own materials, whether a few sentences on a blackboard, a highly-structured fully-realised online course, or anything in between. Despite this, the knowledge and skills needed to create effective language learning materials are rarely part of teacher training, and are mostly learnt by trial and error.
Knowledge and skills frameworks, generally called competency frameworks, for ELT teachers, trainers and managers have existed for a few years now. However, until I created one for my MA dissertation, there wasn’t one drawing together what we need to know and do to be able to effectively produce language learning materials.
This webinar will introduce you to my framework, highlighting the key competencies I identified from my research. It will also show how anybody involved in language teaching (any language, not just English!), teacher training, managing schools or developing language learning materials can benefit from using the framework.
How to Make a Field invisible in Odoo 17Celine George
It is possible to hide or invisible some fields in odoo. Commonly using “invisible” attribute in the field definition to invisible the fields. This slide will show how to make a field invisible in odoo 17.
Instructions for Submissions thorugh G- Classroom.pptxJheel Barad
This presentation provides a briefing on how to upload submissions and documents in Google Classroom. It was prepared as part of an orientation for new Sainik School in-service teacher trainees. As a training officer, my goal is to ensure that you are comfortable and proficient with this essential tool for managing assignments and fostering student engagement.
The Roman Empire A Historical Colossus.pdfkaushalkr1407
The Roman Empire, a vast and enduring power, stands as one of history's most remarkable civilizations, leaving an indelible imprint on the world. It emerged from the Roman Republic, transitioning into an imperial powerhouse under the leadership of Augustus Caesar in 27 BCE. This transformation marked the beginning of an era defined by unprecedented territorial expansion, architectural marvels, and profound cultural influence.
The empire's roots lie in the city of Rome, founded, according to legend, by Romulus in 753 BCE. Over centuries, Rome evolved from a small settlement to a formidable republic, characterized by a complex political system with elected officials and checks on power. However, internal strife, class conflicts, and military ambitions paved the way for the end of the Republic. Julius Caesar’s dictatorship and subsequent assassination in 44 BCE created a power vacuum, leading to a civil war. Octavian, later Augustus, emerged victorious, heralding the Roman Empire’s birth.
Under Augustus, the empire experienced the Pax Romana, a 200-year period of relative peace and stability. Augustus reformed the military, established efficient administrative systems, and initiated grand construction projects. The empire's borders expanded, encompassing territories from Britain to Egypt and from Spain to the Euphrates. Roman legions, renowned for their discipline and engineering prowess, secured and maintained these vast territories, building roads, fortifications, and cities that facilitated control and integration.
The Roman Empire’s society was hierarchical, with a rigid class system. At the top were the patricians, wealthy elites who held significant political power. Below them were the plebeians, free citizens with limited political influence, and the vast numbers of slaves who formed the backbone of the economy. The family unit was central, governed by the paterfamilias, the male head who held absolute authority.
Culturally, the Romans were eclectic, absorbing and adapting elements from the civilizations they encountered, particularly the Greeks. Roman art, literature, and philosophy reflected this synthesis, creating a rich cultural tapestry. Latin, the Roman language, became the lingua franca of the Western world, influencing numerous modern languages.
Roman architecture and engineering achievements were monumental. They perfected the arch, vault, and dome, constructing enduring structures like the Colosseum, Pantheon, and aqueducts. These engineering marvels not only showcased Roman ingenuity but also served practical purposes, from public entertainment to water supply.
2. 1. What's the difference between an interface and an abstract class? An abstract class is a class that is only partially implemented by the programmer. It may contain one or more abstract methods. An abstract method is simply a function definition that serves to tell the programmer that the method must be implemented in a child class. An interface is similar to an abstract class; indeed interfaces occupy the same namespace as classes and abstract classes. For that reason, you cannot define an interface with the same name as a class. An interface is a fully abstract class; none of its methods are implemented and instead of a class sub-classing from it, it is said to implement that interface. Abstract classes can have constants, members, method stubs and defined methods, whereas interfaces can only have constants and methods stubs. Methods and members of an abstract class can be defined with any visibility, whereas all methods of an interface must be defined as public. When inheriting an abstract class, the child class must define the abstract methods, whereas an interface can extend another interface and methods don't have to be defined. A child class can only extend a single abstract (or any other) class, whereas an interface can extend or a class can implement multiple other interfaces. A child class can define abstract methods with the same or less restrictive visibility, whereas a class implementing an interface must define the methods with the exact same visibility. 2. When to use abstract class or interface? Interface is used when you only want to declare which methods and members a class MUST have. Anyone implementing the interface will have to declare and implement the methods listed by the interface. If you also want to have a default implementation, use abstract class. Any class extending the abstract class will have to implement only its abstract methods and members, and will have some default implementation of the other methods of the abstract class, which you may override or not.
3. Finally, you can implement as many interfaces as you want, but only extend one class (being it abstract or not). Keep that on mind before choosing. Abstract class is an incomplete implementation of some concept. This incomplete implementation may be different in different context. Derived class implements the abstract class in its context. Interface defines contract or standard. Implementation of the interface has to follow the contract or standard. Interfaces are more used to set these types of standards or contracts. 3. What does the Serializable interface do? The Serializable interface is just a marker. It means that objects can be serialized, i.e. they can be represented as a bit string and restored from that bit string. For example, both of your classes are serializable because they can be represented as a bit string (or regular string). On the other hand, a class that represents a file handle given out by the operating system cannot be serialized: As soon as the program is finished, that handle is gone, and there is no way to get it back. Reopening the file by file name is not guaranteed to work, since it may have been deleted/moved/changed permissions in the meantime. Serializing objects that don't implement the Serializable interface will result in a NotSerializableException being thrown. 4. How you can force the garbage collection? Garbage collection automatic process and can't be forced. You could request it by calling System.gc(). JVM does not guarantee that GC will be started immediately. Garbage collection is one of the most important feature of Java, Garbage collection is also called automatic memory management as JVM automatically removes the unused variables/objects (value is null) from the memory. User program can't directly free the object from memory, instead it is the job of the garbage collector to automatically free the objects that are no longer referenced by a program. Every class inherits finalize() method from java.lang.Object, the finalize() method is called by garbage collector when it determines no more references to the object exists. In Java, it is good idea to
4. explicitly assign null into a variable when no more in use. I Java on calling System.gc() and Runtime.gc(), JVM tries to recycle the unused objects, but there is no guarantee when all the objects will garbage collected. 5. What is Synchronization in Java? Synchronization is a process of controlling the access of shared resources by the multiple threads in such a manner that only one thread can access one resource at a time. In non synchronized multithreaded application, it is possible for one thread to modify a shared object while another thread is in the process of using or updating the object's value. 6. What is memory leak? A memory leak is where an unreferenced object that will never be used again still hangs around in memory and doesn‘t get garbage collected. 7. What is difference between stringbuffer and stringbuilder? The only difference between StringBuffer and StringBuilder is that StringBuilder is unsynchronized whereas StringBuffer is synchronized. So when the application needs to be run only in a single thread then it is better to use StringBuilder. StringBuilder is more efficient than StringBuffer. Criteria to choose among StringBuffer and StringBuilder If your text can change and will only be accessed from a single thread, use a StringBuilder because StringBuilder is unsynchronized. If your text can changes, and will be accessed from multiple threads, use a StringBuffer because StringBuffer is synchronous. 8. What is the difference between checked and unchecked exceptions? In general, unchecked exceptions represent defects in the program (bugs), which are normally Runtime exceptions.
5. Furthermore, checked exceptions represent invalid conditions in areas outside the immediate control of the program. 9. How does Java allocate stack and heap memory? Each time an object is created in Java it goes into the area of memory known as heap. The primitive variables like int and double are allocated in the stack, if they are local method variables and in the heap if they are member variables (i.e. fields of a class). In Java methods local variables are pushed into stack when a method is invoked and stack pointer is decremented when a method call is completed. In a multi-threaded application each thread will have its own stack but will share the same heap. This is why care should be taken in your code to avoid any concurrent access issues in the heap space. The stack is threadsafe (each thread will have its own stack) but the heap is not threadsafe unless guarded with synchronisation through your code. 10. What is Java Reflection? Reflection is commonly used by programs which require the ability to examine or modify the runtime behavior of applications running in the Java virtual machine. 11. What is JVM? Why Java is called the ‘Platform Independent Programming Language’? JVM, or the Java Virtual Machine, is an interpreter which accepts ‗Bytecode‘ and executes it. Java has been termed as a ‗Platform Independent Language‘ as it primarily works on the notion of ‗compile once, run everywhere‘. Here‘s a sequential step establishing the Platform independence feature in Java: The Java Compiler outputs Non-Executable Codes called ‗Bytecode‘. Bytecode is a highly optimized set of computer instruction which could be executed by the Java Virtual Machine (JVM). The translation into Bytecode makes a program easier to be executed across a wide range of platforms, since all we need is a JVM designed for that particular platform.
6. JVMs for various platforms might vary in configuration, those they would all understand the same set of Bytecode, thereby making the Java Program ‗Platform Independent‘. 12. What is the Difference between JDK and JRE? When asked typical Java Interview Questions most startup Java developers get confused with JDK and JRE. And eventually, they settle for ‗anything would do man, as long as my program runs!!‘ Not quite right if you aspire to make a living and career out of Programming. The ―JDK‖ is the Java Development Kit. I.e., the JDK is bundle of software that you can use to develop Java based software. The ―JRE‖ is the Java Runtime Environment. I.e., the JRE is an implementation of the Java Virtual Machine which actually executes Java programs. Typically, each JDK contains one (or more) JRE‘s along with the various development tools like the Java source compilers, bundling and deployment tools, debuggers, development libraries, etc. 13. What does the ‘static’ keyword mean? We are sure you must be well-acquainted with the Java Basics. Now that we are settled with the initial concepts, let‘s look into the Language specific offerings. Static variable is associated with a class and not objects of that class. For example: public class ExplainStatic { public static String name = "Look I am a static variable"; }
7. We have another class where-in we intend to access this static variable just defined. public class Application { public static void main(String[] args) { System.out.println(ExplainStatic.name) } } We don‘t create object of the class ExplainStatic to access the static variable. We directly use the class name itself: ExplainStatic.name 14. What are the Data Types supported by Java? What is Autoboxing and Unboxing? This is one of the most common and fundamental Java interview questions. This is something you should have right at your finger-tips when asked. The eight Primitive Data types supported by Java are: Byte : 8-bit signed two‘s complement integer. It has a minimum value of -128 and a maximum value of 127 (inclusive) Short: 16-bit signed two‘s complement integer. It has a minimum value of -32,768 and a maximum value of 32,767 (inclusive). Int: 32-bit signed two‘s complement integer. It has a minimum value of -2,147,483,648 and a maximum value of 2,147,483,647 (inclusive) Long: 64-bit signed two‘s complement integer. It has a minimum value of -9,223,372,036,854,775,808 and a maximum value of 9,223,372,036,854,775,807 (inclusive) Float Double
8. Autoboxing: The Java compiler brings about an automatic transformation of primitive type (int, float, double etc.) into their object equivalents or wrapper type (Integer, Float, Double,etc) for the ease of compilation. Unboxing: The automatic transformation of wrapper types into their primitive equivalent is known as Unboxing. 15. What is the difference between STRINGBUFFER and STRING? String object is immutable. i.e, the value stored in the String object cannot be changed. Consider the following code snippet: String myString = ―Hello‖; myString = myString + ‖ Guest‖; When you print the contents of myString the output will be ―Hello Guest‖. Although we made use of the same object (myString), internally a new object was created in the process. That‘s a performance issue. StringBuffer/StringBuilder objects are mutable: StringBuffer/StringBuilder objects are mutable; we can make changes to the value stored in the object. What this effectively means is that string operations such as append would be more efficient if performed using StringBuffer/StringBuilder objects than String objects.
9. String str = ―Be Happy With Your Salary.'' str += ―Because Increments are a myth"; StringBuffer strbuf = new StringBuffer(); strbuf.append(str); System.out.println(strbuf); The Output of the code snippet would be: Be Happy With Your Salary. Because Increments are a myth. 16. What is Function Over-Riding and Over-Loading in Java? This is a very important concept in OOP (Object Oriented Programming) and is a must-know for every Java Programmer. Over-Riding: An override is a type of function which occurs in a class which inherits from another class. An override function ―replaces‖ a function inherited from the base class, but does so in such a way that it is called even when an instance of its class is pretending to be a different type through polymorphism. That probably was a little over the top. The code snippet below should explain things better. public class Car { public static void main (String [] args) { Car a = new Car(); Car b = new Ferrari(); //Car ref, but a Ferrari object
10. a.start(); // Runs the Car version of start() b.start(); // Runs the Ferrari version of start() } } class Car { public void start() { System.out.println("This is a Generic start to any Car"); } }class Ferrari extends Car { public void start() { System.out.println("Let‘s start the Ferrari and go out for a cool Party.");} } Over-Loading: Overloading is the action of defining multiple methods with the same name, but with different parameters. It is unrelated to either overriding or polymorphism. Functions in Java could be overloaded by two mechanisms ideally: Varying the number of arguments. Varying the Data Type. class CalculateArea{ void Area(int length){System.out.println(length*2);}
11. void Area(int length , int width){System.out.println(length*width);} public static void main(String args[]){ CalculateArea obj=new CalculateArea(); obj.Area(10); // Area of a Square obj.Area(20,20); // Area of a Rectangle } } 17. What is Constructors, Constructor Overloading in Java and Copy- Constructor? Constructors form the basics of OOPs, for starters. Constructor: The sole purpose of having Constructors is to create an instance of a class. They are invoked while creating an object of a class. Here are a few salient features of Java Constructors: Constructors can be public, private, or protected. If a constructor with arguments has been defined in a class, you can no longer use a default no-argument constructor – you have to write one. They are called only once when the class is being instantiated. They must have the same name as the class itself. They do not return a value and you do not have to specify the keyword void. If you do not create a constructor for the class, Java helps you by using a so called default no-argument constructor.
12. public class Boss{ String name; Boss(String input) { //This is the constructor name = "Our Boss is also known as : " + input; } public static void main(String args[]) { Boss p1 = new Boss("Super-Man"); } } Constructor overloading: passing different number and type of variables as arguments all of which are private variables of the class. Example snippet could be as follows: public class Boss{ String name; Boss(String input) { //This is the constructor name = "Our Boss is also known as : " + input; } Boss() { name = "Our Boss is a nice man. We don‘t call him names.‖;
13. } public static void main(String args[]) { Boss p1 = new Boss("Super-Man"); Boss p2 = new Boss(); } } Copy Constructor: A copy constructor is a type of constructor which constructs the object of the class from another object of the same class. The copy constructor accepts a reference to its own class as a parameter.
18. What is Java Exception Handling? What is the difference between Errors, Unchecked Exception and Checked Exception? Anything that‘s not Normal is an exception. Exceptions are the customary way in Java to indicate to a calling method that an abnormal condition has occurred. In Java, exceptions are objects. When you throw an exception, you throw an object. You can‘t throw just any object as an exception, however — only those object whose classes descend from Throwable. Throwable serves as the base class for an entire family of classes, declared in java.lang, that your program can instantiate and throw. Here‘s a hierarchical Exception class structure: An Unchecked Exception inherits from RuntimeException (which extends from Exception). The JVM treats RuntimeException differently as there is no requirement for the application-code to deal with them explicitly. A Checked Exception inherits from the Exception-class. The client code has to handle the checked exceptions either in a try-catch
14. clause or has to be thrown for the Super class to catch the same. A Checked Exception thrown by a lower class (sub-class) enforces a contract on the invoking class (super-class) to catch or throw it. Errors (members of the Error family) are usually thrown for more serious problems, such as OutOfMemoryError (OOM), that may not be so easy to handle. Exception handling needs special attention while designing large applications. So we would suggest you to spend some time brushing up your Java skills. 19. What is the difference between Throw and Throws in Java Exception Handling? Throws: A throws clause lists the types of exceptions that a method might throw, thereby warning the invoking method – ‗Dude. You need to handle this list of exceptions I might throw.‘ Except those of type Error or RuntimeException, all other Exceptions or any of their subclasses, must be declared in the throws clause, if the method in question doesn‘t implement a try…catch block. It is therefore the onus of the next-on-top method to take care of the mess. public void myMethod() throws PRException {..} This means the super function calling the function should be equipped to handle this exception. public void Callee() { try{ myMethod();
15. }catch(PRException ex) { ...handle Exception....} } Using the Throw: If the user wants to throw an explicit Exception, often customized, we use the Throw. The Throw clause can be used in any part of code where you feel a specific exception needs to be thrown to the calling method. try{ if(age>100){throw new AgeBarException(); //Customized ExceptioN }else{ ....} } }catch(AgeBarException ex){ ...handle Exception..... } 20. What is the Difference between Byte stream and Character streams? Every Java Programmer deals with File Operations. To generate User reports, send attachments through mails and spill out data files from Java programs. And a sound knowledge on File Operation becomes even more important while dealing with Java questions.
16. Byte stream: For reading and writing binary data, byte stream is incorporated. Programs use byte streams to perform byte input and output. Performing InputStream operations or OutputStream operations means generally having a loop that reads the input stream and writes the output stream one byte at a time. You can use buffered I/O streams for an overhead reduction (overhead generated by each such request often triggers disk access, network activity, or some other operation that is relatively expensive). Character streams: Character streams work with the characters rather than the byte. In Java, characters are stored by following the Unicode (allows a unique number for every character) conventions. In such kind of storage, characters become the platform independent, program independent, language independent.
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