OOP Interview Questions 1. What is OOPS? OOPS is abbreviated as Object Oriented Programming system in which programs are considered as a collection of objects. Each object is nothing but an instance of a class. 2. Write basic concepts of OOPS? Following are the concepts of OOPS and are as follows:. 1. Abstraction. 2. Encapsulation. 3. Inheritance. 4. Polymorphism. 3. What is a class? A class is simply a representation of a type of object. It is the blueprint/ plan/ template that describe the details of an object. 4. What is an object? Object is termed as an instance of a class, and it has its own state, behavior and identity. 5. What is Encapsulation? Encapsulation is an attribute of an object, and it contains all data which is hidden. That hidden data can be restricted to the members of that class. Levels are Public,Protected, Private, Internal and Protected Internal. 6. What is Polymorphism? Polymorphism is nothing butassigning behavior or value in a subclass to something that was already declared in the main class. Simply, polymorphism takes more than one form. 7. What is Inheritance? Inheritance is a concept where one class shares the structure and behavior defined in another class. Ifinheritance applied on one class is called Single Inheritance, and if it depends on multiple classes, then it is called multiple Inheritance. 8. What are manipulators? Manipulators are the functions which can be used in conjunction with the insertion (<<) and extraction (>>) operators on an object. Examples are endl and setw. 9. Define a constructor? Constructor is a method used to initialize the state of an object, and it gets invoked at the time of object creation. Rules forconstructor are:. Constructor Name should be same asclass name. Constructor must have no return type. 10. Define Destructor? Destructor is a method which is automatically called when the object ismade ofscope or destroyed. Destructor name is also same asclass name but with the tilde symbol before the name. 11. What is Inline function? Inline function is a technique used by the compilers and instructs to insert complete body of the function wherever that function is used in the program source code. 12. What is avirtual function?
Virtual function is a member function ofclass and its functionality can be overridden in its derived class. This function can be implemented by using a keyword called virtual, and it can be given during function declaration. Virtual function can be achieved in C++, and it can be achieved in C Languageby using function pointers or pointers to function. 13. What isfriend function? Friend function is a friend of a class that is allowed to access to Public, private or protected data in that same class. If the function is defined outside the class cannot access such information. Friend can be declared anywhere in the class declaration, and it cannot be affected by access control keywords like private, public or protected. 14. What is function overloading? Function overloading is defined as a normal function, but it has the ability to perform different tasks. It allowscreation of several methods with the same name which differ from each other by type of input and output of the function. Example void add(int& a, int& b); void add(double& a, double& b); void add(struct bob& a, struct bob& b); 15. What is operator overloading? Operator overloading is a function where different operators are applied and depends on the arguments. Operator,-,* can be used to pass through the function, and it has their own precedence to execute. Example: 1 class complex { 2 double real, 3 imag; public: complex(double r, double i) : real(r), 4 imag(i) {} complex operator+(complex a, complex b); 5 complex operator*(complex a, complex b); 6 complex& operator=(complex a, complex b); 7 } a=1.2, b=6 16. What is an abstract class? An abstract class is a class which cannot be instantiated. Creation of an object is not possible with abstract class, but it can be inherited. An abstract class can contain only Abstract method. Java allows only abstract method in abstract class while for other language it allows non-abstract method as well. 17. What is a ternary operator? Ternary operator is said to be an operator which takes three arguments. Arguments and results are of different data types, and it is depends on the function. Ternary operator is also called asconditional operator. 18. What is the use of finalize method?
Finalize method helps to perform cleanup operations on the resources which are not currently used. Finalize method is protected, and it is accessible only through this class or by a derived class. 19. What are different types of arguments? A parameter is a variable used during the declaration of the function or subroutine and arguments are passed to the function, and it should match with the parameter defined. There are two types of Arguments. Call by Value Value passed will get modified only inside the function, and it returns the same value whatever it is passed it into the function. Call by Reference Value passed will get modified in both inside and outside the functions and it returns the same or different value. 20. What is super keyword? Super keyword is used to invoke overridden method which overrides one of its superclass methods. This keyword allows to access overridden methods and also to access hidden members of the superclass. It also forwards a call from a constructor to a constructor in the superclass. 21. What is method overriding? Method overriding is a feature that allows sub class to provide implementation of a method that is already defined in the main class. This will overrides the implementation in the superclass by providing the same method name, same parameter and same return type. 22. What is an interface? An interface is a collection of abstract method. If the class implements an inheritance, and then thereby inherits all the abstract methods of an interface. 23. What is exception handling? Exception is an event that occurs during the execution of a program. Exceptions can be of any type Run time exception, Error exceptions. Those exceptions are handled properly through exception handling mechanism like try, catch and throw keywords. 24. What are tokens? Token is recognized by a compiler and it cannot be broken down into component elements. Keywords, identifiers, constants, string literals and operators are examples of tokens. Even punctuation characters are also considered as tokens Brackets, Commas, Braces and Parentheses. 25. Difference between overloading and overriding? Overloading is static binding whereas Overriding is dynamic binding. Overloading is nothing but the same method with different arguments, and it may or may not return the same value in the same class itself. Overriding is the same method names with same arguments and return types associates with the class and its child class. 26. Difference between class and an object? An object is an instance of a class. Objects hold any information, but classes don t have any information. Definition of properties and functions can be done at class and can be used by the object. Class can have sub-classes, and an object doesn t have sub-objects. 27. What is an abstraction?
Abstraction is a good feature of OOPS, and it shows only the necessary details to the client of an object. Means, it shows only necessary details for an object, not the inner details of an object. Example When you want to switch On television, it not necessary to show all the functions of TV. Whatever is required to switch on TV will be showed by using abstract class. 28. What are access modifiers? Access modifiers determine the scope of the method or variables that can be accessed from other various objects or classes. There are 5 types of access modifiers, and they are as follows:. Private. Protected. Public. Friend. Protected Friend. 29. What is sealed modifiers? Sealed modifiers are the access modifiers where it cannot be inherited by the methods. Sealed modifiers can also be applied to properties, events and methods. This modifier cannot be applied to static members. 30. How can we call the base method without creating an instance? Yes, it is possible to call the base method without creating an instance. And that method should be,static method. Doing inheritance from that class.-use Base Keyword from derived class. 31. What is the difference between new and override? The new modifier instructs the compiler to use the new implementation instead of the base class function. Whereas, Override modifier helps to override the base class function. 32. What are the various types of constructors? There are three various types of constructors, and they are as follows:. Default Constructor With no parameters. Parametric Constructor With Parameters. Create a new instance of a class and also passing arguments simultaneously. Copy Constructor Which creates a new object as a copy of an existing object. 33. What is early and late binding? Early binding refers to assignment of values to variables during design time whereas late binding refers to assignment of values to variables during run time. 34. What is this pointer? THIS pointer refers to the current object of a class. THIS keyword is used as a pointer which differentiates between the current object with the global object. Basically, it refers to the current object. 35. What is the difference betweenstructure and a class? Structure default access type is public, but class access type is private. A structure is used for grouping data whereas class can be used for grouping data and methods. Structures are exclusively used for dataand it doesn t require strict validation, but classes are used to encapsulates and inherit data which requires strict validation.
36. What is the default access modifier in a class? The default access modifier of a class is Private by default. 37. What is pure virtual function? A pure virtual function is a function which can be overridden in the derived classbut cannot be defined. A virtual function can be declared as Pure by using the operator =0. Example -. 1 Virtual void function1() // Virtual, Not pure 2 3 Virtual void function2() = 0 //Pure virtual 38. What are all the operators that cannot be overloaded? Following are the operators that cannot be overloaded -. 1. Scope Resolution (:: ) 2. Member Selection (.) 3. Member selection through a pointer to function (.*) 39. What is dynamic or run time polymorphism? Dynamic or Run time polymorphism is also known as method overriding in which call to an overridden function is resolved during run time, not at the compile time. It means having two or more methods with the same name,same signature but with different implementation. 40. Do we require parameter for constructors? No, we do not require parameter for constructors. 41. What is a copy constructor? This is a special constructor for creating a new object as a copy of an existing object. There will be always only on copy constructor that can be either defined by the user or the system. 42. What does the keyword virtual represented in the method definition? It means, we can override the method. 43. Whether static method can use non static members? False. 44. What arebase class, sub class and super class? Base class is the most generalized class, and it is said to be a root class. Sub class is a class that inherits from one or more base classes. Super class is the parent class from which another class inherits. 45. What is static and dynamic binding? Binding is nothing but the association of a name with the class. Static binding is a binding in which name can be associated with the class during compilation time, and it is also called as early Binding. Dynamic binding is a binding in which name can be associated with the class during execution time, and it is also called as Late Binding. 46. How many instances can be created for an abstract class? Zero instances will be created for an abstract class. 47. Which keyword can be used for overloading? Operator keyword is used for overloading.
48. What is the default access specifier in a class definition? Private access specifier is used in a class definition. 49. Which OOPS concept is used as reuse mechanism? Inheritance is the OOPS concept that can be used as reuse mechanism. 50. Which OOPS concept exposes only necessary information to the calling functions? Data Hiding / Abstraction CPP Interview Questions 1) What is the full form of OOPS? Object Oriented Programming System. 2) What is a class? Class is a blue print which reflects the entities attributes and actions. Technically defining a class is designing an user defined data type. 3) What is an object? An instance of the class is called as object. 4) List the types of inheritance supported in C++. Single, Multilevel, Multiple, Hierarchical and Hybrid. 5) What is the role of protected access specifier? If a class member is protected then it is accessible in the inherited class. However, outside the both the private and protected members are not accessible. 6)What is encapsulation? The process of binding the data and the functions acting on the data together in an entity (class) called as encapsulation. 7) What is abstraction? Abstraction refers to hiding the internal implementation and exhibiting only the necessary details. 8) What is inheritance? Inheritance is the process of acquiring the properties of the existing class into the new class. The existing class is called as base/parent class and the inherited class is called as derived/child class. 9) Explain the purpose of the keyword volatile. Declaring a variable volatile directs the compiler that the variable can be changed externally. Hence avoiding compiler optimization on the variable reference. 10) What is an inline function? A function prefixed with the keyword inline before the function definition is called as inline function. The inline functions are faster in execution when compared to normal functions as the compiler treats inline functions as macros. 11) What is a storage class? Storage class specifies the life or scope of symbols such as variable or functions. 12) Mention the storage classes names in C++. The following are storage classes supported in C++ auto, static, extern, register and mutable
13) What is the role of mutable storage class specifier? A constant class object s member variable can be altered by declaring it using mutable storage class specifier. Applicable only for non-static and non-constant member variable of the class. 14) Distinguish between shallow copy and deep copy. Shallow copy does memory dumping bit-by-bit from one object to another. Deep copy is copy field by field from object to another. Deep copy is achieved using copy constructor and or overloading assignment operator. 15) What is a pure virtual function? A virtual function with no function body and assigned with a value zero is called as pure virtual function. 16) What is an abstract class in C++? A class with at least one pure virtual function is called as abstract class. We cannot instantiate an abstract class. 17) What is a reference variable in C++? A reference variable is an alias name for the existing variable. Which mean both the variable name and reference variable point to the same memory location. Therefore updation on the original variable can be achieved using reference variable too. 18) What is role of static keyword on class member variable? A static variable does exit though the objects for the respective class are not created. Static member variable share a common memory across all the objects created for the respective class. A static member variable can be referred using the class name itself. 19) Explain the static member function. A static member function can be invoked using the class name as it exits before class objects comes into existence. It can access only static members of the class. 20) Name the data type which can be used to store wide characters in C++. wchar_t 21) What are/is the operator/operators used to access the class members? Dot (.) and Arrow ( -> ) 22) Can we initialize a class/structure member variable as soon as the same is defined? No, Defining a class/structure is just a type definition and will not allocated memory for the same. 23) What is the data type to store the Boolean value? bool, is the new primitive data type introduced in C++ language. 24) What is function overloading? Defining several functions with the same name with unique list of parameters is called as function overloading. 25) What is operator overloading? Defining a new job for the existing operator w.r.t the class objects is called as operator overloading. 26) Do we have a String primitive data type in C++? No, it s a class from STL (Standard template library). 27) Name the default standard streams in C++. cin, cout, cerr and clog.
28) Which access specifier/s can help to achive data hiding in C++? Private & Protected. 29) When a class member is defined outside the class, which operator can be used to associate the function definition to a particular class? Scope resolution operator (::) 30) What is a destructor? Can it be overloaded? A destructor is the member function of the class which is having the same name as the class name and prefixed with tilde (~) symbol. It gets executed automatically w.r.t the object as soon as the object loses its scope. It cannot be overloaded and the only form is without the parameters. 31) What is a constructor? A constructor is the member function of the class which is having the same as the class name and gets executed automatically as soon as the object for the respective class is created. 32) What is a default constructor? Can we provide one for our class? Every class does have a constructor provided by the compiler if the programmer doesn t provides one and known as default constructor. A programmer provided constructor with no parameters is called as default constructor. In such case compiler doesn t provides the constructor. 33) Which operator can be used in C++ to allocate dynamic memory? new is the operator can be used for the same. 34) What is the purpose of delete operator? delete operator is used to release the dynamic memory which was created using new operator. 35) Can I use malloc() function of C language to allocate dynamic memory in C++? Yes, as C is the subset of C++, we can all the functions of C in C++ too. 36) Can I use delete operator to release the memory which was allocated using malloc() function of C language? No, we need to use free() of C language for the same. 37) What is a friend function? A function which is not a member of the class but still can access all the member of the class is called so. To make it happen we need to declare within the required class following the keyword friend. 38) What is a copy constructor? A copy constructor is the constructor which take same class object reference as the parameter. It gets automatically invoked as soon as the object is initialized with another object of the same class at the time of its creation. 39) Does C++ supports exception handling? If so what are the keywords involved in achieving the same. C++ does supports exception handling. try, catch & throw are keyword used for the same. 40) Explain the pointer this. This, is the pointer variable of the compiler which always holds the current active object s address. 41) What is the difference between the keywords struct and class in C++?
By default the members of struct are public and by default the members of the class are private. 42) Can we implement all the concepts of OOPS using the keyword struct? Yes. 43) What is the block scope variable in C++? A variable whose scope is applicable only within a block is said so. Also a variable in C++ can be declared anywhere within the block. 44) What is the role of the file opening mode ios::trunk? If the file already exists, its content will be truncated before opening the file. 45) What is the scope resolution operator? The scope resolution operator is used to Resolve the scope of global variables. To associate function definition to a class if the function is defined outside the class. 46) What is a namespace? A namespace is the logical division of the code which can be used to resolve the name conflict of the identifiers by placing them under different name space. 47) What are command line arguments? The arguments/parameters which are sent to the main() function while executing from the command line/console are called so. All the arguments sent are the strings only. 48) What is a class template? A template class is a generic class. The keyword template can be used to define a class template. 49) How can we catch all kind of exceptions in a single catch block? The catch block with ellipses as follows catch( ) { } 50) What is keyword auto for? By default every local variable of the function is automatic (auto). In the below function both the variables i and j are automatic variables. void f() { int i; auto int j; } NOTE: A global variable can t be an automatic variable. 51) What is the purpose of extern storage specifier. Used to resolve the scope of global symbol #include <iostream> using namespace std;
main() { extern int i; cout<<i<<endl; } int i=20; 52) What is the meaning of base address of the array? The starting address of the array is called as the base address of the array. 53) When should we use the register storage specifier? If a variable is used most frequently then it should be declared using register storage specifier, then possibly the compiler gives CPU register for its storage to speed up the look up of the variable. 54) Can a program be compiled without main() function? Yes, it can be but cannot be executed, as the execution requires main() function definition. 55) Where an automatic variable is stored? Every local variable by default being an auto variable is stored in stack memory 56) What is a container class? A class containing at least one member variable of another class type in it is called so. 57) What is a token? A C++ program consists of various tokens and a token is either a keyword, an identifier, a constant, a string literal, or a symbol. 58) What is a preprocessor? Preprocessor is a directive to the compiler to perform certain things before the actual compilation process begins. 59) What are command line arguments? The arguments which we pass to the main() function while executing the program are called as command line arguments. The parameters are always strings held in the second argument (below in args) of the function which is array of character pointers. First argument represents the count of arguments (below in count) and updated automatically by operating system. main( int count, char *args[]) { } 60) What are the different ways of passing parameters to the functions? Which to use when? Call by value: We send only values to the function as parameters. We choose this if we do not want the actual parameters to be modified with formal parameters but just used. Call by address: We send address of the actual parameters instead of values. We choose this if we do want the actual parameters to be modified with formal parameters.
Call by reference: The actual parameters are received with the C++ new reference variables as formal parameters. We choose this if we do want the actual parameters to be modified with formal parameters. 61) What is reminder for 5.0 % 2? Error, It is invalid that either of the operands for the modulus operator (%) is a real number. 62) Which compiler switch to be used for compiling the programs using math library with g++ compiler? Opiton lm to be used as > g++ lm <file.cpp> 63) Can we resize the allocated memory which was allocated using new operator? No, there is no such provision available. 64) Who designed C++ programming language? Bjarne Stroustrup. 65) Which operator can be used to determine the size of a data type/class or variable/object?how can we refer to the global variable if the local and the global variable names are same? We can apply scope resolution operator (::) to the for the scope of global variable. 66) What are valid operations on pointers? The only two permitted operations on pointers are Comparision ii) Addition/Substraction (excluding void pointers) 67) What is recursion? Function calling itself is called as recursion. 68) What is the first string in the argument vector w.r.t command line arguments? Program name. 69) What is the maximum length of an identifier? Ideally it is 32 characters and also implementation dependent. 70) What is the default function call method? By default the functions are called by value. 71) What are available mode of inheritance to inherit one class from another? Public, private & protected 72) What is the difference between delete and delete[]? Delete[] is used to release the array allocated memory which was allocated using new[] and delete is used to release one chunk of memory which was allocated using new. 73) Does an abstract class in C++ need to hold all pure virtual functions? Not necessarily, a class having at least one pure virtual function is abstract class too. 74) Is it legal to assign a base class object to a derived class pointer? No, it will be error as the compiler fails to do conversion. 75) What happens if an exception is thrown outside a try block? The program shall quit abruptly. 76) Are the exceptions and error same? No, exceptions can be handled whereas program cannot resolve errors. 77) What is function overriding? Defining the functions within the base and derived class with the same signature and name where the base class s function is virtual.
78) Which function is used to move the stream pointer for the purpose of reading data from stream? seekg() 79) Which function is used to move the stream pointer for the purpose of writing data from stream? seekp() 80) Are class functions taken into consideration as part of the object size? No, only the class member variables determines the size of the respective class object. 81) Can we create and empty class? If so what would be the size of such object. We can create an empty class and the object size will be 1. 82) What is std? Default namespace defined by C++. 83) What is the full form of STL? Standard template library 84) What is cout? cout is the object of ostream class. The stream cout is by default connected to console output device. 85) What is cin? cin is the object of istream class. The stream cin is by default connected to console input device. 86) What is the use of the keyword using? It is used to specify the namespace being used in. 87) If a pointer declared for a class, which operator can be used to access its class members? Arrow (->) operator can be used for the same 88) What is difference between including the header file with-in angular braces < > and double quotes If a header file is included with in < > then the compiler searches for the particular header file only with in the built in include path. If a header file is included with in, then the compiler searches for the particular header file first in the current working directory, if not found then in the built in include path 89) S++ or S=S+1, which can be recommended to increment the value by 1 and why? S++, as it is single machine instruction (INC) internally. 90) What is the difference between actual and formal parameters? The parameters sent to the function at calling end are called as actual parameters while at the receiving of the function definition called as formal parameters. 91) What is the difference between variable declaration and variable definition? Declaration associates type to the variable whereas definition gives the value to the variable. 92) Which key word is used to perform unconditional branching? goto. 93) Is 068 a valid octal number? No, it contains invalid octal digits. 94) What is the purpose of #undef preprocessor? It will be used to undefine an existing macro definition.
95) Can we nest multi line comments in a C++ code? No, we cannot. 96) What is a virtual destructor? A virtual destructor ensures that the objects resources are released in the reverse order of the object being constructed w.r.t inherited object. 97) What is the order of objects destroyed in the memory? The objects are destroyed in the reverse order of their creation. 98) What is a friend class? A class members can gain accessibility over other class member by placing the class declaration prefixed with the keyword friend in the destination class. 99) What is a static variable? A static local variables retains its value between the function call and the default value is 0. The following function will print 1 2 3 if called thrice. void f() { static int i; ++i; printf( %d,i); } If a global variable is static then its visibility is limited to the same source code. Core Java - Interview Questions 1.what is a transient variable? A transient variable is a variable that may not be serialized. 2.which containers use a border Layout as their default layout? The window, Frame and Dialog classes use a border layout as their default layout. 3.Why do threads block on I/O? Threads block on i/o (that is enters the waiting state) so that other threads may execute while the i/o Operation is performed. 4. How are Observer and Observable used? Objects that subclass the Observable class maintain a list of observers. When an Observable object is updated it invokes the update() method of each of its observers to notify the observers that it has changed state. The Observer interface is implemented by objects that observe Observable objects. 5. What is synchronization and why is it important? With respect to multithreading, synchronization is the capability to control the access of multiple threads to shared resources. Without synchronization, it is possible for one thread to
modify a shared object while another thread is in the process of using or updating that object's value. This often leads to significant errors. 6. Can a lock be acquired on a class? Yes, a lock can be acquired on a class. This lock is acquired on the class's Class object. 7. What's new with the stop(), suspend() and resume() methods in JDK 1.2? The stop(), suspend() and resume() methods have been deprecated in JDK 1.2. 8. Is null a keyword? The null value is not a keyword. 9. What is the preferred size of a component? The preferred size of a component is the minimum component size that will allow the component to display normally. 10. What method is used to specify a container's layout? The setlayout() method is used to specify a container's layout. 11. Which containers use a FlowLayout as their default layout? The Panel and Applet classes use the FlowLayout as their default layout. 12. What state does a thread enter when it terminates its processing? When a thread terminates its processing, it enters the dead state. 13. What is the Collections API? The Collections API is a set of classes and interfaces that support operations on collections of objects. 14. Which characters may be used as the second character of an identifier, but not as the first character of an identifier? The digits 0 through 9 may not be used as the first character of an identifier but they may be used after the first character of an identifier. 15. What is the List interface? The List interface provides support for ordered collections of objects. 16. How does Java handle integer overflows and underflows? It uses those low order bytes of the result that can fit into the size of the type allowed by the operation. 17. What is the Vector class? The Vector class provides the capability to implement a growable array of objects 18. What modifiers may be used with an inner class that is a member of an outer class? A (non-local) inner class may be declared as public, protected, private, static, final, or abstract. 19. What is an Iterator interface? The Iterator interface is used to step through the elements of a Collection. 20. What is the difference between the >> and >>> operators? The >> operator carries the sign bit when shifting right. The >>> zero-fills bits that have been shifted out. 21. Which method of the Component class is used to set the position and size of a component? setbounds()
22. How many bits are used to represent Unicode, ASCII, UTF-16, and UTF-8 characters? Unicode requires 16 bits and ASCII require 7 bits. Although the ASCII character set uses only 7 bits, it is usually represented as 8 bits. UTF-8 represents characters using 8, 16, and 18 bit patterns. UTF-16 uses 16-bit and larger bit patterns. 23What is the difference between yielding and sleeping? When a task invokes its yield() method, it returns to the ready state. When a task invokes its sleep() method, it returns to the waiting state. 24. Which java.util classes and interfaces support event handling? The EventObject class and the EventListener interface support event processing. 25. Is sizeof a keyword? The sizeof operator is not a keyword. 26. What are wrapped classes? Wrapped classes are classes that allow primitive types to be accessed as objects. 27. Does garbage collection guarantee that a program will not run out of memory? Garbage collection does not guarantee that a program will not run out of memory. It is possible for programs to use up memory resources faster than they are garbage collected. It is also possible for programs to create objects that are not subject to garbage collection 28. What restrictions are placed on the location of a package statement within a source code file? A package statement must appear as the first line in a source code file (excluding blank lines and comments). 29. Can an object's finalize() method be invoked while it is reachable? An object's finalize() method cannot be invoked by the garbage collector while the object is still reachable. However, an object's finalize() method may be invoked by other objects. 30. What is the immediate superclass of the Applet class? Panel 31. What is the difference between preemptive scheduling and time slicing? Under preemptive scheduling, the highest priority task executes until it enters the waiting or dead states or a higher priority task comes into existence. Under time slicing, a task executes for a predefined slice of time and then reenters the pool of ready tasks. The scheduler then determines which task should execute next, based on priority and other factors. 32. Name three Component subclasses that support painting. The Canvas, Frame, Panel, and Applet classes support painting. 33. What value does readline() return when it has reached the end of a file? The readline() method returns null when it has reached the end of a file. 34. What is the immediate superclass of the Dialog class? Window 35. What is clipping? Clipping is the process of confining paint operations to a limited area or shape. 36. What is a native method? A native method is a method that is implemented in a language other than Java. 37. Can a for statement loop indefinitely? Yes, a for statement can loop indefinitely. For example, consider the following:
for(;;) ; 38. What are order of precedence and associativity, and how are they used? Order of precedence determines the order in which operators are evaluated in expressions. Associatity determines whether an expression is evaluated left-to-right or right-to-left 39. When a thread blocks on I/O, what state does it enter? A thread enters the waiting state when it blocks on I/O. 40. To what value is a variable of the String type automatically initialized? The default value of an String type is null. 41. What is the catch or declare rule for method declarations? If a checked exception may be thrown within the body of a method, the method must either catch the exception or declare it in its throws clause. 42. What is the difference between a MenuItem and a CheckboxMenuItem? The CheckboxMenuItem class extends the MenuItem class to support a menu item that may be checked or unchecked. 43. What is a task's priority and how is it used in scheduling? A task's priority is an integer value that identifies the relative order in which it should be executed with respect to other tasks. The scheduler attempts to schedule higher priority tasks before lower priority tasks. 44. What class is the top of the AWT event hierarchy? The java.awt.awtevent class is the highest-level class in the AWT event-class hierarchy. 45. When a thread is created and started, what is its initial state? A thread is in the ready state after it has been created and started. 46. Can an anonymous class be declared as implementing an interface and extending a class? An anonymous class may implement an interface or extend a superclass, but may not be declared to do Both. 47. What is the range of the short type? The range of the short type is -(2^15) to 2^15-1. 48. What is the range of the char type? The range of the char type is 0 to 2^16-1. 49. In which package are most of the AWT events that support the event-delegation model defined? Most of the AWT-related events of the event-delegation model are defined in the java.awt.event package. The AWTEvent class is defined in the java.awt package. 50. What is the immediate superclass of Menu? MenuItem 51. What is the purpose of finalization? The purpose of finalization is to give an unreachable object the opportunity to perform any cleanup processing before the object is garbage collected. 52. Which class is the immediate superclass of the MenuComponent class. Object 53. What invokes a thread's run() method? After a thread is started, via its start() method or that of the Thread class, the JVM invokes the thread's run() method when the thread is initially executed.
54. What is the difference between the Boolean & operator and the && operator? If an expression involving the Boolean & operator is evaluated, both operands are evaluated. Then the & operator is applied to the operand. When an expression involving the && operator is evaluated, the first operand is evaluated. If the first operand returns a value of true then the second operand is evaluated. The && operator is then applied to the first and second operands. If the first operand evaluates to false, the evaluation of the second operand is skipped. 55. Name three subclasses of the Component class. Box.Filler, Button, Canvas, Checkbox, Choice, Container, Label, List, Scrollbar, or TextComponent 56. What is the GregorianCalendar class? The GregorianCalendar provides support for traditional Western calendars. 57. Which Container method is used to cause a container to be laid out and redisplayed? validate() 58. What is the purpose of the Runtime class? The purpose of the Runtime class is to provide access to the Java runtime system. 59. How many times may an object's finalize() method be invoked by the garbage collector? An object's finalize() method may only be invoked once by the garbage collector. 60. What is the purpose of the finally clause of a try-catch-finally statement? The finally clause is used to provide the capability to execute code no matter whether or not an exception is thrown or caught. 61. What is the argument type of a program's main() method? A program's main() method takes an argument of the String[] type. 62. Which Java operator is right associative? The = operator is right associative. 63. What is the Locale class? The Locale class is used to tailor program output to the conventions of a particular geographic, political, or cultural region. 64. Can a double value be cast to a byte? Yes, a double value can be cast to a byte. 65. What is the difference between a break statement and a continue statement? A break statement results in the termination of the statement to which it applies (switch, for, do, or while). A continue statement is used to end the current loop iteration and return control to the loop statement. 66. What must a class do to implement an interface? It must provide all of the methods in the interface and identify the interface in its implements clause. 67. What method is invoked to cause an object to begin executing as a separate thread? The start() method of the Thread class is invoked to cause an object to begin executing as a separate thread. 68. Name two subclasses of the TextComponent class. TextField and TextArea
69. What is the advantage of the event-delegation model over the earlier eventinheritance model? The event-delegation model has two advantages over the event-inheritance model. First, it enables event handling to be handled by objects other than the ones that generate the events (or their containers). This allows a clean separation between a component's design and its use. The other advantage of the event-delegation model is that it performs much better in applications where many events are generated. This performance improvement is due to the fact that the event-delegation model does not have to repeatedly process unhandled events, as is the case of the event-inheritance model. 70. Which containers may have a MenuBar? Frame 71. How are commas used in the initialization and iteration parts of a for statement? Commas are used to separate multiple statements within the initialization and iteration parts of a for statement. 72. What is the purpose of the wait(), notify(), and notifyall() methods? The wait(),notify(), and notifyall() methods are used to provide an efficient way for threads to wait for a shared resource. When a thread executes an object's wait() method, it enters the waiting state. It only enters the ready state after another thread invokes the object's notify() or notifyall() methods. 73. What is an abstract method? An abstract method is a method whose implementation is deferred to a subclass. 74. How are Java source code files named? A Java source code file takes the name of a public class or interface that is defined within the file. A source code file may contain at most one public class or interface. If a public class or interface is defined within a source code file, then the source code file must take the name of the public class or interface. If no public class or interface is defined within a source code file, then the file must take on a name that is different than its classes and interfaces. Source code files use the.java extension. 75. What is the relationship between the Canvas class and the Graphics class? A Canvas object provides access to a Graphics object via its paint() method. 76. What are the high-level thread states? The high-level thread states are ready, running, waiting, and dead. 77. What value does read() return when it has reached the end of a file? The read() method returns -1 when it has reached the end of a file. 78. Can a Byte object be cast to a double value? No, an object cannot be cast to a primitive value. 79. What is the difference between a static and a non-static inner class? A non-static inner class may have object instances that are associated with instances of the class's outer class. A static inner class does not have any object instances. 80. What is the difference between the String and StringBuffer classes? String objects are constants. StringBuffer objects are not. 81. If a variable is declared as private, where may the variable be accessed? A private variable may only be accessed within the class in which it is declared. 82. What is an object's lock and which object's have locks?
An object's lock is a mechanism that is used by multiple threads to obtain synchronized access to the object. A thread may execute a synchronized method of an object only after it has acquired the object's lock. All objects and classes have locks. A class's lock is acquired on the class's Class object. 83. What is the Dictionary class? The Dictionary class provides the capability to store key-value pairs. 84. How are the elements of a BorderLayout organized? The elements of a BorderLayout are organized at the borders (North, South, East, and West) and the center of a container. 85. What is the % operator? It is referred to as the modulo or remainder operator. It returns the remainder of dividing the first operand by the second operand. 86. When can an object reference be cast to an interface reference? An object reference be cast to an interface reference when the object implements the referenced interface. 87. What is the difference between a Window and a Frame? The Frame class extends Window to define a main application window that can have a menu bar. 88. Which class is extended by all other classes? The Object class is extended by all other classes. 89. Can an object be garbage collected while it is still reachable? A reachable object cannot be garbage collected. Only unreachable objects may be garbage collected.. 90. Is the ternary operator written x : y? z or x? y : z? It is written x? y : z. 91. What is the difference between the Font and FontMetrics classes? The FontMetrics class is used to define implementation-specific properties, such as ascent and descent, of a Font object. 92. How is rounding performed under integer division? The fractional part of the result is truncated. This is known as rounding toward zero. 93. What happens when a thread cannot acquire a lock on an object? If a thread attempts to execute a synchronized method or synchronized statement and is unable to acquire an object's lock, it enters the waiting state until the lock becomes available. 94. What is the difference between the Reader/Writer class hierarchy and the InputStream/ OutputStream class hierarchy? The Reader/Writer class hierarchy is character-oriented, and the InputStream/OutputStream class hierarchy is byte-oriented. 95. What classes of exceptions may be caught by a catch clause? A catch clause can catch any exception that may be assigned to the Throwable type. This includes the Error and Exception types. 96. If a class is declared without any access modifiers, where may the class be accessed?
A class that is declared without any access modifiers is said to have package access. This means that the class can only be accessed by other classes and interfaces that are defined within the same package. 97. What is the SimpleTimeZone class? The SimpleTimeZone class provides support for a Gregorian calendar. 98. What is the Map interface? The Map interface replaces the JDK 1.1 Dictionary class and is used associate keys with values. 99. Does a class inherit the constructors of its superclass? A class does not inherit constructors from any of its superclasses. 100. For which statements does it make sense to use a label? The only statements for which it makes sense to use a label are those statements that can enclose a break or continue statement. 101. What is the purpose of the System class? The purpose of the System class is to provide access to system resources. 102. Which TextComponent method is used to set a TextComponent to the read-only state? seteditable() 103. How are the elements of a CardLayout organized? The elements of a CardLayout are stacked, one on top of the other, like a deck of cards. 104. Is &&= a valid Java operator? No, it is not. 105. Name the eight primitive Java types. The eight primitive types are byte, char, short, int, long, float, double, and boolean. 106. Which class should you use to obtain design information about an object? The Class class is used to obtain information about an object's design. 107. What is the relationship between clipping and repainting? When a window is repainted by the AWT painting thread, it sets the clipping regions to the area of the window that requires repainting. 108. Is "abc" a primitive value? The String literal "abc" is not a primitive value. It is a String object. 109. What is the relationship between an event-listener interface and an event-adapter class? An event-listener interface defines the methods that must be implemented by an event handler for a particular kind of event. An event adapter provides a default implementation of an event-listener interface. 110. What restrictions are placed on the values of each case of a switch statement? During compilation, the values of each case of a switch statement must evaluate to a value that can be promoted to an int value. 111. What modifiers may be used with an interface declaration? An interface may be declared as public or abstract. 112. Is a class a subclass of itself? A class is a subclass of itself. 113. What is the highest-level event class of the event-delegation model?
The java.util.eventobject class is the highest-level class in the event-delegation class hierarchy. 114. What event results from the clicking of a button? The ActionEvent event is generated as the result of the clicking of a button. 115. How can a GUI component handle its own events? A component can handle its own events by implementing the required event-listener interface and adding itself as its own event listener. 116. What is the difference between a while statement and a do statement? A while statement checks at the beginning of a loop to see whether the next loop iteration should occur. A do statement checks at the end of a loop to see whether the next iteration of a loop should occur. The do statement will always execute the body of a loop at least once. 117. How are the elements of a GridBagLayout organized? The elements of a GridBagLayout are organized according to a grid. However, the elements are of different sizes and may occupy more than one row or column of the grid. In addition, the rows and columns may have different sizes. 118. What advantage do Java's layout managers provide over traditional windowing systems? Java uses layout managers to lay out components in a consistent manner across all windowing platforms. Since Java's layout managers aren't tied to absolute sizing and positioning, they are able to accommodate platform-specific differences among windowing systems. 119. What is the Collection interface? The Collection interface provides support for the implementation of a mathematical bag - an unordered collection of objects that may contain duplicates. 120. What modifiers can be used with a local inner class? A local inner class may be final or abstract. 121. What is the difference between static and non-static variables? A static variable is associated with the class as a whole rather than with specific instances of a class. Non-static variables take on unique values with each object instance. 122. What is the difference between the paint() and repaint() methods? The paint() method supports painting via a Graphics object. The repaint() method is used to cause paint() to be invoked by the AWT painting thread. 123. What is the purpose of the File class? The File class is used to create objects that provide access to the files and directories of a local file system. 124. Can an exception be rethrown? Yes, an exception can be rethrown. 125. Which Math method is used to calculate the absolute value of a number? The abs() method is used to calculate absolute values. 126. How does multithreading take place on a computer with a single CPU? The operating system's task scheduler allocates execution time to multiple tasks. By quickly switching between executing tasks, it creates the impression that tasks execute sequentially. 127. When does the compiler supply a default constructor for a class?