Java Classes Questions And Answers

41⟩ When a member is declared static, it CANNOT be accessed before any objects of its class are created, and without reference to any objectA) TrueB) False

Explanation: When a member is declared static, it can be accessed before any objects of its class are created, and without reference to any object. You can declare both methods and variables to be static.

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42⟩ In the Call-by-value methods of passing an argument to a Subroutine, the value of an argument is copied into the formal parameter of the subroutineA) TrueB) False

True

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43⟩ Obtaining objects of a class is a ____ -step processA) oneB) TwoC) ThreeD) Four

Explanation: Obtaining objects of a class is a two-step process. First, you must declare a variable of the class type. This variable does not define an object. Instead, it is simply a variable that can refer to an object. Second, you must acquire an actual, physical copy of the object and assign it to that variable.

two step process

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44⟩ What is singleton class and how can we get it from a general class,explain with examples(program)?

In computer science, the singleton design pattern is designed to restrict instantiation of a class to one (or a few) objects. This is useful when exactly one object is needed to coordinate actions across the system. Sometimes it is generalized to systems that operate more efficiently when only one or a few objects exist.

The singleton pattern is implemented by creating a class with a method that creates a new instance of the object if one does not exist. If one does exist it returns a reference to the object that already exists. To make sure that the object cannot be instantiated any other way the constructor is made either private or protected.

The singleton pattern must be carefully constructed in multi-threaded applications. If two threads are to execute the creation method at the same time when a singleton does not yet exist, they both must check for an instance of the singleton and then only one should create the new one.

The classic solution to this problem is to use mutual exclusion on the class that indicates that the object is being instantiated.

A Java programming language solution is as follows. It is based on the Q&A link found below, modified for multi-threading, however, it is still vulnerable to the double-checked locking anti-pattern, also found below:

public class Singleton {

private static Singleton INSTANCE = null;

// Private constructor suppresses

// default public constructor

private Singleton() {}

//synchronized creator to defend against multi-threading issues

//another if check here to avoid multiple instantiation

private synchronized static void createInstance() {

if (INSTANCE == null) {

INSTANCE = new Singleton();

}

public static Singleton getInstance() {

if (INSTANCE == null) createInstance();

return INSTANCE;

}

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45⟩ In this example type name(parameter-list) { // body of method}type specifies the type of data returned by the methodA) TrueB) False

True

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46⟩ What is the significance of wait() method with respect to Object class, not in Thread class?

the wait() method is defined in the java.lang.OBject() class and not in the java.lang.Thread()class. it's signature is public static void wait(). we do have some overloaded versions of the wait() method. when an wait method is called by an thread on a object it release the lock on the object and goes to an WAIT/BLOCKED state inorder to let the other threads to enter the RUNNING state. However it regains the Lock on the object after sometime when it moves from the WAIT/BLOCKED state to RUNNABLE state . that can happen due to the call of notify(),notifyAll() methods by other threads holding of the respective objects Lock.

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47⟩ How to create console or how i can take result with the help of console?

we can create console by using system.in class.

and also readline().

for example

BufferedInputStream br=new BuffereInputStream(new InputstreamReader(System.in));

br.readLine();//reading the values from console.

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48⟩ Recursion is the process of defining something in terms of itself.A) TrueB) False

Ans : true.

Recursion is the process which calls itself.

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49⟩ J2SE 5 has added a new feature that simplifies the creation of methods that need to take a variable number of arguments. This feature is called _______A) varargs

Explanation: varargs - It is short for variable-length arguments.

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50⟩ Method overloading is one of the ways that Java supports ____________A) EncapsulationB) ClassC) InheritanceD) Polymorphism

With method overloading Java supports polymorphism.

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51⟩ finalize( ) is only called just prior to _________A) InitialisationB) RuntimeC) Garbage CollectionD) None of the above

Ans is : Garbage Collection

b'coz the finalize() method is called by the garbage collector when it determines no more references to the object exist.

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52⟩ Sometimes a method will need to refer to the object that invoked it. To allow this, Java defines the_____ keywordA) thisB) thatC) theD) and

Ans : this.

B'coz 'this' keyword is used to point to the current object.

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53⟩ When an overloaded method is invoked, Java uses the type and/or number of arguments as its guide to determine which version of the overloaded method to actually callA) TrueB) False

a) true

the type and number of args is together known as the signature of a method

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54⟩ In general, there are _________ ways that a computer language can pass an argument to a subroutineA) OneB) TwoC) ThreeD) Four

Explanation: In general, there are two ways that a computer language can pass an argument to a subroutine. The first way is call-by-value. The second way an argument can be passed is call-by-reference.

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55⟩ Through _________ , you can control what parts of a program can access the members of a classA) EncapsulationB) ClassC) InheritanceD) Polymorphism

a)Encapsulation

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56⟩ What is Class Loader?

Class loaders are one of the cornerstones of the Java virtual machine (JVM) architecture. They enable the JVM to load classes without knowing anything about the underlying file system semantics, and they allow applications to dynamically load Java classes as extension modules.A class loader is an object that is responsible for loading classes. The class ClassLoader is an abstract class. Given the name of a class, a class loader should attempt to locate or generate data that constitutes a definition for the class. A typical strategy is to transform the name into a file name and then read a "class file" of that name from a file system.

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57⟩ A variable declared as final prevents its contents from being modifiedA) TrueB) False

ans is true.

when we a final keyword to a variable the value of the variable can't change.

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58⟩ Deallocation of memory in Java is called Garbage CollectionA) TrueB) False

True, deallocation is called Garbage Collection

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59⟩ If you want to pass information into a program when you run it then command-line arguments are to main( )A) TrueB) False

True.

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60⟩ The Code in java is contained within MethodsA) TrueB) False

Source Code is normally an entire file.

In Java the actual execution (or result preparation) would be there in methods only.Method will return exact one return value / 0(void).

Methods will change the behaviour of an object (Operations).

Fields contains value or state of an object.

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Java Classes

Home Java Programing Java Classes

76 Java Classes Questions And Answers

41⟩ When a member is declared static, it CANNOT be accessed before any objects of its class are created, and without reference to any objectA) TrueB) False

42⟩ In the Call-by-value methods of passing an argument to a Subroutine, the value of an argument is copied into the formal parameter of the subroutineA) TrueB) False

43⟩ Obtaining objects of a class is a ____ -step processA) oneB) TwoC) ThreeD) Four

44⟩ What is singleton class and how can we get it from a general class,explain with examples(program)?

45⟩ In this example type name(parameter-list) { // body of method}type specifies the type of data returned by the methodA) TrueB) False

46⟩ What is the significance of wait() method with respect to Object class, not in Thread class?

47⟩ How to create console or how i can take result with the help of console?

48⟩ Recursion is the process of defining something in terms of itself.A) TrueB) False

49⟩ J2SE 5 has added a new feature that simplifies the creation of methods that need to take a variable number of arguments. This feature is called _______A) varargs

50⟩ Method overloading is one of the ways that Java supports ____________A) EncapsulationB) ClassC) InheritanceD) Polymorphism

51⟩ finalize( ) is only called just prior to _________A) InitialisationB) RuntimeC) Garbage CollectionD) None of the above

52⟩ Sometimes a method will need to refer to the object that invoked it. To allow this, Java defines the_____ keywordA) thisB) thatC) theD) and

53⟩ When an overloaded method is invoked, Java uses the type and/or number of arguments as its guide to determine which version of the overloaded method to actually callA) TrueB) False

54⟩ In general, there are _________ ways that a computer language can pass an argument to a subroutineA) OneB) TwoC) ThreeD) Four

55⟩ Through _________ , you can control what parts of a program can access the members of a classA) EncapsulationB) ClassC) InheritanceD) Polymorphism

56⟩ What is Class Loader?

57⟩ A variable declared as final prevents its contents from being modifiedA) TrueB) False

58⟩ Deallocation of memory in Java is called Garbage CollectionA) TrueB) False

59⟩ If you want to pass information into a program when you run it then command-line arguments are to main( )A) TrueB) False

60⟩ The Code in java is contained within MethodsA) TrueB) False

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Java Classes

Home Java Programing Java Classes

76 Java Classes Questions And Answers

41⟩ When a member is declared static, it CANNOT be accessed before any objects of its class are created, and without reference to any objectA) TrueB) False

42⟩ In the Call-by-value methods of passing an argument to a Subroutine, the value of an argument is copied into the formal parameter of the subroutineA) TrueB) False

43⟩ Obtaining objects of a class is a ____ -step processA) oneB) TwoC) ThreeD) Four

44⟩ What is singleton class and how can we get it from a general class,explain with examples(program)?

45⟩ In this example type name(parameter-list) { // body of method}type specifies the type of data returned by the methodA) TrueB) False

46⟩ What is the significance of wait() method with respect to Object class, not in Thread class?

47⟩ How to create console or how i can take result with the help of console?

48⟩ Recursion is the process of defining something in terms of itself.A) TrueB) False

49⟩ J2SE 5 has added a new feature that simplifies the creation of methods that need to take a variable number of arguments. This feature is called _______A) varargs

50⟩ Method overloading is one of the ways that Java supports ____________A) EncapsulationB) ClassC) InheritanceD) Polymorphism

51⟩ finalize( ) is only called just prior to _________A) InitialisationB) RuntimeC) Garbage CollectionD) None of the above

52⟩ Sometimes a method will need to refer to the object that invoked it. To allow this, Java defines the_____ keywordA) thisB) thatC) theD) and

53⟩ When an overloaded method is invoked, Java uses the type and/or number of arguments as its guide to determine which version of the overloaded method to actually callA) TrueB) False

54⟩ In general, there are _________ ways that a computer language can pass an argument to a subroutineA) OneB) TwoC) ThreeD) Four

55⟩ Through _________ , you can control what parts of a program can access the members of a classA) EncapsulationB) ClassC) InheritanceD) Polymorphism

56⟩ What is Class Loader?

57⟩ A variable declared as final prevents its contents from being modifiedA) TrueB) False

58⟩ Deallocation of memory in Java is called Garbage CollectionA) TrueB) False

59⟩ If you want to pass information into a program when you run it then command-line arguments are to main( )A) TrueB) False

60⟩ The Code in java is contained within MethodsA) TrueB) False

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