Chapter 1 : Chapter-wise Java Multiple Choice Questions and Answers Interview MCQs Java Programming questions and answers with explanation for interview, competitive examination and entrance test. Fully solved examples with detailed answer description, explanation are given and it would be easy to understand. What is the range of data type short in Java? What is the range of data type byte in Java? An expression involving byte, int, and literal numbers is promoted to which of these? Which of these literals can be contained in a data type float variable? Which data type value is returned by all transcendental math functions? Which of the following can be operands of arithmetic operators? Decrement operator, â, decreases value of variable by what number? Which of these statements are incorrect? Applets Questions and Answers 1. Which of these functions is called to display the output of an applet? Applets Questions and Answers 2. Which of these methods can be used to output a sting in an applet? Applets Questions and Answers 3. What does AWT stands for? Applets Questions and Answers 4. Applets Questions and Answers 5. Which of these modifiers can be used for a variable so that it can be accessed from any thread or parts of a program? Arrays Questions and Answers 1. Which of these operators is used to allocate memory to array variable in Java? Arrays Questions and Answers 2. Which of these is an incorrect array declaration? Arrays Questions and Answers 3. What will this code print? Which of these is an incorrect Statement? Arrays Questions and Answers 5. Which of these is necessary to specify at time of array initialization? Collections Questions and Answers 1. Which of these packages contain all the collection classes? Collections Questions and Answers 2. Collections Questions and Answers 3. Collections Questions and Answers 4. Which of these methods deletes all the elements from invoking collection? Collections Questions and Answers 5. What is Collection in Java? When does Exceptions in Java arises in code sequence? Which of these keywords is not a part of exception handling? Which of these keywords must be used to monitor for exceptions? Which of these keywords must be used to handle the exception thrown by try block in some rational manner? Which of these keywords is used to manually throw an exception? Input Output Streams Questions and Answers 1. Input Output Streams Questions and Answers 2. Input Output Streams Questions and Answers 3. Which of these is a type of stream in Java? Input Output Streams Questions and Answers 4. Which of these classes are used by Byte streams for input and output operation? Input Output Streams Questions and Answers 5. Which of these classes are used by character streams for input and output operations? Which of these keywords is used to define interfaces in Java? Which of these can be used to fully abstract a class from its implementation? Which of these access specifiers can be used for an interface? Which of these keywords is used by a class to use an interface defined previously? Which of the following is correct way of implementing an interface salary by class manager? Which of these class is not a member class of java. Which of these interface is not a member of java. Which of these class is not related to input and output stream in terms of functioning? Which of these is specified by a File object? Which of these classes is not included in java. Which of these is a process of converting a simple data type into a class? Which of these is wrapper for simple data type float? Which of the following is method of wrapper Float for converting the value of an object into byte? Which of these standard collection classes implements a dynamic array? Which of these class can generate an array which can increase and decrease in size automatically? Which of these method can be used to increase the capacity of ArrayList object manually? Which of these method of ArrayList class is used to obtain present size of an object? Which of these methods can be used to obtain a static array from an ArrayList object? Packages Questions and Answers 1. Which of these keywords is used to define packages in Java? Packages Questions and Answers 2. Which of these is a mechanism for naming and visibility control of a class and its content? Packages Questions and Answers 3. Which of this access specifies can be used for a class so that its members can be accessed by a different class in the same package? Packages Questions and Answers 4. Packages Questions and Answers 5. Serialization Questions and Answers 1. Which of these is a process of writing the state of an object to a byte stream? Serialization Questions and Answers 2. Which of these process occur automatically by java run time system? Serialization Questions and Answers 3. Which of these is an interface for control over serialization and deserialization? Serialization Questions and Answers 4. Which of these interface extends DataOutput Page 1
interface? Serialization Questions and Answers 5. Which of these is a method of ObjectOutput interface used to finalize the output state so that any buffers are cleared? Strings Questions and Answers 1. Which of these class is superclass of String and StringBuffer class? Strings Questions and Answers 2. Which of these operators can be used to concatenate two or more String objects? Strings Questions and Answers 3. Which of these method of class String is used to obtain length of String object? Strings Questions and Answers 4. Which of these method of class String is used to extract a single character from a String object? Strings Questions and Answers 5. Which of these constructors is used to create an empty String object? Which of these method can be used to make the main thread to be executed last among all the threads? Which of these method is used to find out that a thread is still running or not? Which of these method waits for the thread to treminate? Which of these method is used to explicitly set the priority of a thread? Fully solved examples with detailed answer description, explanation are given and it would be easy to understand. This page provides a great collection of Java Questions on a single page along with their correct answers and explanations. Page 2
Chapter 2 : Java Aptitude Questions and Answers Java Aptitude Questions and Answers Our Java Aptitude Questions and Answers focused on all topics of Java Programming Language. Here we are providing Aptitude Solutions with Programs, Examples, Multiple Choice Questions and correct answer. Specially developed for the freshers, these 30 solved Core Java questions will help you prepare for technical interviews and online selection tests during campus placement. After reading these tricky Core Java questions, you can easily attempt the objective type and multiple choice type questions on Core Java. The Polymorphism can be referred as one name many forms. It is the ability of methods to behave differently, depending upon the object who is calling it. The key features of Polymorphism are: Allows using one interface for multiple implementations. Multiple methods with same name, but different formal argument. Multiple methods have the same name, same return type, and same formal argument list. The Java uses the garbage collection to free the memory. By cleaning those objects that are no longer reference by any of the program. Step involve in cleaning up the garbage collection: First step is to collection and group all those object which are no more reference with any of the program. We can use the different methods to collect the garbage object like using runtime. To free up those object which is collected by the garbage collector java must execute the Finalize method to delete all those dynamically created object. What is an immutable object? An immutable object is one that we cannot change once it is created. Steps involved in creation of an immutable object are: How are this and super used with constructors? What are Access Specifiers available in Java? Java offers four access specifiers, described below: Public classes, methods, and fields can be accessed by every class. Protected methods and fields can only be accessed within the same class to which the methods and fields belong. When we do not set access to specific level, then such a class, method, or field will be accessible from inside the same package to which the class, method, or field belongs. Private methods and fields can only be accessed within the same class to which the methods and fields belong. Private methods and fields are not inherited by subclasses. What are the List interface and its main implementation? The List helps in collections of objects. Lists may contain duplicate elements. The main implementations of the List interface are as follows: Resizable-array implementation of the List interface. Synchronized resizable-array implementation of the List. Doubly-linked list implementation of the List interface. Better performance than the ArrayList implementation when elements are inserted or deleted timely. Explain the user defined Exceptions. User Defined Exceptions are exceptions defined by the user for specific purposed. This allows custom exceptions to be generated and caught in the same way as normal exceptions. While defining a User Defined Exception, we need to take care of the following aspects: Describe life cycle of thread. Threads follow the single flow of control. A thread is execution in a program. The life cycles of threads are listed below: After the creations of Thread instance the thread is in this state but before the start method invocation. Thread is considered not alive in this phase. A thread starts its life from Runnable state. After the invoking of start method thread enters Runnable state. A thread first enters Runnable state. A thread can enter in this state because of waiting the resources that are hold by another thread. A thread can be considered dead when its run method completes. If any thread comes on this state that means it cannot ever run again. What is an Applets? What is the Set interface? What is a HashSet and TreeSet? How do you decide when to use HashMap and when to use TreeMap and what is difference between these two? Depending upon the size of collection, adding elements to HashMap is easy. For sorted elements traversal we can convert the HashMap into TreeMap. What is the Comparable interface? The value of i returned will be negative. The value of i returned will be positive. The value of i returned will be zero. When should I use abstract classes and when should I use interfaces? Use Abstract Class, when: Explain the Polymorphism principle. It is the ability of the methods to behave differently, depending upon the object who is calling it. Method overriding through inheritance 3. Method overriding through the java interface What are the difference between throw and throws? The difference between throw and throws are: What is difference between preemptive scheduling and time slicing? Differences between preemptive and time scheduling are: The scheduler then determines which task should execute next, based on priority and other Page 3
factor. Explain traversing through a collector using Iterator. We can access each element in the collection by using Iterators irrespective of how they are organized in the collector. Iterator can be implemented a different way for every Collection. To use an iterator to traverse through the contents of a collection we do: Have the loop iterate as long as hasnext returns true. What are the principle concepts of OOPS? There are four principle concepts upon which object oriented design and programming test. Abstraction refers to the act of representing essential features without including the background details or explanations. It is the ability to create a variable, a function, or an object that has more than one form. Inheritance is the process by which objects of one class acquire the properties of objects of another class. Encapsulation is a technique used for hiding the properties and behaviors of an object and allowing outside access only as appropriate. It prevents other objects from directly altering or accessing the properties or methods of the encapsulated object. What are the basic features of java? The basic features of java are given below: Page 4
Chapter 3 : Core Java - Interview Questions and Answers Technical interview questions and answers section on "Core Java" with explanation for various interview, competitive examination and entrance test. Solved examples with detailed answer description, explanation are given and it would be easy to understand. Exception is an abnormal condition which occurs during the execution of a program and disrupts normal flow of the program. This exception must be handled properly. If it is not handled, program will be terminated abruptly. Exceptions in java are handled using try, catch and finally blocks. The code or set of statements which are to be monitored for exception are kept in this block. This block catches the exceptions occurred in the try block. This block is always executed whether exception is occurred in the try block or not and occurred exception is caught in the catch block or not. Errors are mainly caused by the environment in which an application is running. Where as exceptions are mainly caused by the application itself. For example, NullPointerException occurs when an application tries to access null object. They form a one unit. No, It shows compilation error. The try block must be followed by either catch or finally block. You can remove either catch block or finally block but not both. After that there is a catch block to catch the exceptions occurred in the try block. Assume that exception has occurred in statement2. Does statement3 get executed or not? Once a try block throws an exception, remaining statements will not be executed. When you are keeping multiple catch blocks, the order of catch blocks must be from most specific to most general ones. If you keep super classes first and sub classes later, compiler will show unreachable catch block error. Click here to see the hierarchy of exceptions in java. The exceptions which occur at run time are called as run time exceptions. These exceptions are unknown to compiler. All sub classes of java. Error are run time exceptions. OutOfMemoryError is the sub class of java. Error which occurs when JVM runs out of memory. Checked exceptions are the exceptions which are known to compiler. These exceptions are checked at compile time only. Hence the name checked exceptions. These exceptions are also called compile time exceptions. Because, these exceptions will be known during compile time. Unchecked exceptions are those exceptions which are not at all known to compiler. These exceptions occur only at run time. These exceptions are also called as run time exceptions. Error are unchecked exceptions. Click here to see more about checked and unchecked exceptions. No, it gives unreachable code error. Because, control is returning from the finally block itself. Compiler will not see the statements after it. Yes, we can throw an exception manually using throw keyword. Syntax for throwing an exception manually is throw InstanceOfThrowableType; Below example shows how to use throw keyword to throw an exception manually. If it is unable to handle that exception, it can re-throw that exception using throw keyword. It is called re-throwing an exception. Click here to see the uses of throws keyword in java. Because finally block is always executed whether exceptions are raised in the try block or not and raised exceptions are caught in the catch block or not. By keeping the clean up operations in finally block, you will ensure that those operations will be always executed irrespective of whether exception is occurred or not. Click here to see the differences between final, finally and finalize in java. Click here to see about customized exceptions in java. Click here to see the differences between throw, throws and throwable in java. If a super class method is throwing an unchecked exception, then it can be overridden in the sub class with same exception or any other unchecked exceptions but can not be overridden with checked exceptions. Click here to see about chained exceptions in java. Throwable is the super class for all types of errors and exceptions in java. Page 5
Chapter 4 : Java Multiple Choice Questions and Answers Core Java Interview Questions Set 1 90% assurance of interview questions. There is the list of core java interview questions. If there is any core java interview question that has been asked to you, kindly post it in the ask question section. Openings for and pass outs MNC in india. What is the most Important feature of java? Java is platform independent language. What do you mean by Platform Independence? What is JIT Compiler? JIT compiles parts of the byte code that have similar functionality at the same time, 5. What if main method declare as private? No,It will compile fine but in run time it will error like main method should be in public. A platform is basically the hardware or software environment in which a program runs. There are two types of platforms software and hardware. Java provides software-based platform. What all memory areas are allocated by JVM? What is the base class of all classes? It is the intermediate representation of your source code that contains instructions. Can we mark constructors final? No, Constructor cannot be declared final. What are two different ways to call garbage collector? Can we override a static method? No, we cannot override a static method. Static means class level. Use of finalize method in java? Is it possible to overload main method of a class? Yes, we can overload main method as well. But every time public static main String[] args will be called automatically by JVM. Other methods need to call explicitly. Does Java support operator overloading? Operator overloading is not supported in Java. Can I declare a data type inside loop in java? Any Data type declaration should not be inside the loop. Its possible but not recommended. List two java ID Es? Net beans and 3. Can we inherit the constructors? No, we cannot inherit constructors. We can call super class constructors from subclass constructor by using super call. Can this keyword be assigned null value? No, this keyword cannot have null values assigned to it. Basic java interview programs for freshers Check out these basic java programs for beginners. Page 6
Chapter 5 : Core Java - Java (MCQ) questions and answers When a string is created in java, it's actually an object of blog.quintoapp.com class that gets created. After creation of this string object, all built-in methods of String class can be used on the string object. What is the difference between an Inner Class and a Sub-Class? An Inner class is a class which is nested within another class. An Inner class has access rights for the class which is nesting it and it can access all variables and methods defined in the outer class. A sub-class is a class which inherits from another class called super class. Sub-class can access all public and protected methods and fields of its super class. What are the various access specifiers for Java classes? In Java, access specifiers are the keywords used before a class name which defines the access scope. The types of access specifiers for classes are: Class,Method,Field is accessible from anywhere. Method,Field can be accessed from the same class to which they belong or from the sub-classes,and from the class of same package,but not from outside. Method,Field can be accessed from the same class to which they belong. When there is a requirement to share a method or a variable between multiple objects of a class instead of creating separate copies for each object, we use static keyword to make a method or variable shared for all objects. Encapsulation is a concept in Object Oriented Programming for combining properties and methods in a single unit. Encapsulation helps programmers to follow a modular approach for software development as each object has its own set of methods and variables and serves its functions independent of other objects. Encapsulation also serves data hiding purpose. What is a singleton class? Give a practical example of its usage. A singleton class in java can have only one instance and hence all its methods and variables belong to just one instance. Singleton class concept is useful for the situations when there is a need to limit the number of objects for a class. The best example of singleton usage scenario is when there is a limit of having only one connection to a database due to some driver limitations or because of any licensing issues. What are Loops in Java? What are three types of loops? Looping is used in programming to execute a statement or a block of statement repeatedly. There are three types of loops in Java: For loops are used when number of times to execute the statements is known to programmer. In while loops, condition is checked first before execution of statements. Hence in case of do while loop, statements are executed at least once. What is an infinite Loop? How infinite loop is declared? An infinite loop runs without any condition and runs infinitely. An infinite loop can be broken by defining any breaking logic in the body of the statement blocks. Infinite loop is declared as follows: What is the difference between continue and break statement? When a break keyword is used in a loop, loop is broken instantly while when continue keyword is used, current iteration is broken and loop continues with next iteration. In below example, Loop is broken when counter reaches 4. What is the difference between double and float variables in Java? In java, float takes 4 bytes in memory while Double takes 8 bytes in memory. Float is single precision floating point decimal number while Double is double precision decimal number. What is Final Keyword in Java? In java, a constant is declared using the keyword Final. This method are faster than any other method,because they are resolved at complied time. When a class is declares as final,it cannot be subclassed. Example String,Integer and other wrapper classes. What is ternary operator? Ternary operator, also called conditional operator is used to decide which value to assign to a variable based on a Boolean value evaluation. In the below example, if rank is 1, status is assigned a value of "Done" else "Pending". How can you generate random numbers in Java? What is default switch case? In a switch statement, default case is executed when no other switch condition matches. Default case is an optional case. It can be declared only once all other switch cases have been coded. In the below example, when score is not 1 or 2, default case is used. Can main method in Java can return any data? What are Java Packages? In Java, package is a collection of classes and interfaces which are bundled together as they are related to each other. Use of packages helps developers to modularize the code and group the code for proper re-use. Once code has been packaged in Packages, it can be imported in other classes and used. Can we declare a class as Abstract without having any abstract method? However, if a class has even one abstract method, it must be declared as abstract otherwise it will give an error. The primary difference between an abstract class and interface is that an interface can only possess declaration of public static methods with no Page 7
concrete implementation while an abstract class can have members with any access specifiers public, private etc with or without concrete implementation. A class can implement multiple interfaces but it can extend only one abstract class. What are the performance implications of Interfaces over abstract classes? Interfaces are slower in performance as compared to abstract classes as extra indirections are required for interfaces. Another key factor for developers to take into consideration is that any class can extend only one abstract class while a class can implement many interfaces. Use of interfaces also puts an extra burden on the developers as any time an interface is implemented in a class; developer is forced to implement each and every method of interface. Does Importing a package imports its sub-packages as well in Java? For example, if a developer imports a package university. To load the classes from its sub-package say department, developer has to import it explicitly as follows: Can we declare the main method of our class as private? In java, main method must be public static in order to run any application correctly. How can we pass argument to a function by reference instead of pass by value? In java, we can pass argument to a function only by value and not by reference. How an object is serialized in java? In java, to convert an object into byte stream by serialization, an interface with the name Serializable is implemented by the class. All objects of a class implementing serializable interface get serialized and their state is saved in byte stream. When we should use serialization? Serialization is used when data needs to be transmitted over the network. The byte stream is transferred over the network and the object is re-created at destination. Try block needs to be followed by either Catch block or Finally block or both. Any exception thrown from try block needs to be either caught in the catch block or else any specific tasks to be performed before code abortion are put in the Finally block. Is there any way to skip Finally block of exception even if some exception occurs in the exception block? If an exception is raised in Try block, control passes to catch block if it exists otherwise to finally block. Finally block is always executed when an exception occurs and the only way to avoid execution of any statements in Finally block is by aborting the code forcibly by writing following line of code at the end of try block: When the constructor of a class is invoked? The constructor of a class is invoked every time an object is created with new keyword. For example, in the following class two objects are created using new keyword and hence, constructor is invoked two times. Can a class have multiple constructors? Yes, a class can have multiple constructors with different parameters. Which constructor gets used for object creation depends on the arguments passed while creating the objects. Can we override static methods of a class? We cannot override static methods. Static methods belong to a class and not to individual objects and are resolved at the time of compilation not at runtime. Even if we try to override static method,we will not get an complitaion error,nor the impact of overriding when running the code. In the below example, what will be the output? Displaying from superclass Q Is String a data type in java? String is not a primitive data type in java. String class that gets created. After creation of this string object, all built-in methods of String class can be used on the string object. Chapter 6 : Java Programming Questions and Answers The section contains questions and answers on various concepts of blog.quintoapp.com like data types, types of classes, character and byte streams, builtin exceptions, rounding functions, system class, byte, short, double and float wrappers, character and boolean wrappers and environment properties. Chapter 7 : 30 Core Java Interview Questions and Answers for Freshers These objective type Core Java questions are very important for campus placement test and job interviews. Specially developed for the Networking freshers and professionals, these model questions are asked in the online technical test and interview of many IT companies. Chapter 8 : Java Online Quiz - TutorialsPoint Java Multiple Choice Questions and Answers Java Programming questions and answers with explanation for interview, Page 8
competitive examination and entrance test. Fully solved examples with detailed answer description, explanation are given and it would be easy to understand. Chapter 9 : Online Random Test + Questions: Yes, more than questions with detailed answers covering most important areas of core java interview such as core java concepts, strings, collection framework, multi-threading, concurrency, exception handling etc. Page 9