SE2019 Java

A class defines only the properties for objects. True. False.

Creating an object is referred to as instantiation. True. False.

Each class in the source code is written into a .class file. True. False.

class file is compiled into .java file. True. False.

Constructors must have the same name as the class itself. True. False.

Constructors can be overloaded for making it easy to construct objects with different initial data values. True. False.

A class may be defined without constructors. True. False.

A class is essentially a built-in primitive type. True. False.

Reference data fields in class are initialized by default to the zero value. True. False.

Static variables are also known as class variables. True. False.

All objects of the class share its instance variables. True. False.

A class method cannot access instance members (i.e., instance data fields and instance methods) of the class. True. False.

Static methods can be called without creating an object of the class. True. False.

All objects of the class share constants in a class. True. False.

Static methods and static data fields can be accessed from their class name. True. False.

An instance method can invoke an instance or static method, and access an instance or static data field. True. False.

Java provides the private and protected visibility modifiers for class and class members. True. False.

If we want to prohibit the user from creating an instance of a class, we should use a private constructor. True. False.

To enable a private data field to be updated, we should provide an accessor method to set a new value in it. True. False.

The object is actually passed by value to a method. True. False.

When an array of objects is created, each element in the array is a reference variable with a default value of null. True. False.

An object whose contents cannot be changed once the object has been created is called immutable object. True. False.

A class with all private data fields and no mutators is necessarily immutable. True. False.

A variable defined inside a method is referred to as a local variable. True. False.

The scope of a class’s variables (instance and static) is the entire class, regardless of where the variables are declared. True. False.

If a local variable has the same name as a class’s variable, the class’s variable takes precedence and the local variable with the same name is hidden. True. False.

The keyword this refers to a class's data field hidden by a method or constructor local parameter, or to invoke an overloaded constructor by the calling object itself. True. False.

In OOP, class abstraction concept separates class implementation details from how the class is used. True. False.

A primitive-type value is not an object, but it can be wrapped in an object using a wrapper class in the Java API. True. False.

Converting a primitive value to a wrapper object is called boxing and the reverse conversion is called unboxing. True. False.

Wrapper classes of primitive types are imported from the java.util package. True. False.

wrapper classes do not have no-argument constructors. True. False.

The instances of all wrapper classes are immutable. True. False.

The Double wrapper class can be used to represent decimals of any size and precision. True. False.

A String object is mutable. True. False.

Inheritance is used to model the has-a relationship between classes. True. False.

Private members of a super class can be used directly in a subclass. True. False.

A Java class may inherit directly from only one superclass. True. False.

A subclass is not a subset of a superclass because it usually contains more variables and methods than its superclass. True. False.

When constructing an object of a subclass, the subclass constructor must first invoke its superclass constructor before performing its own tasks. True. False.

to override a method, the method must be defined in the subclass using the same signature and the same return type. True. False.

A private method in a superclass cannot be overridden in a subclass. True. False.

A static method in a superclass can be overridden in a subclass. True. False.

Method overloading means to provide a new implementation for a method in the subclass. True. False.

Overridden methods can be either in the same class, or in different classes related by inheritance. True. False.

Every class in Java is by default extending from the Object class. True. False.

Polymorphism means that a reference variable of a superclass can refer to a subclass object. True. False.

You can always successfully cast an instance of a superclass to a subclass reference variable. True. False.

The == operator can be used to check whether two objects have the same contents or not. True. False.

ArrayList object is used to store a dynamic list of primitive values or objects. True. False.

Subclass cannot weaken the accessibility of a method defined in the superclass. True. False.

A class with no modifier is accessible by classes from other packages. True. False.

The protected visibility modifier enable the members of the class to be accessed by the subclasses in any package or classes in the same package. True. False.

A method defined as final in a superclass cannot be overridden in the subclasses. True. False.

An abstract class can be used to create objects. True. False.

It is not possible to define an abstract class that does not contain any abstract methods. True. False.

A subclass can be abstract even if its superclass is non-abstract. True. False.

Abstract methods must not be static. True. False.

Each interface is compiled into a separate bytecode file, just like a regular class. True. False.

You cannot create a new instance from an interface. True. False.

A class cannot implement multiple interfaces. True. False.

In abstract class definition, all variables must be public static final. True. False.

An interface can inherit other multiple interfaces using the extends keyword. True. False.

Interface must not contain constructors. True. False.

Interface can be as a data type for a reference variable, as the result of casting, and so on. True. False.

The operator …….. is used to access a data field or invoke a method from an object. – (Dash). . (Dot). -> (Arrow). _ (Underscore).

A class provides method of a special type, known as ………, which is invoked to create a new instance. final. ٍstatic. abstract. constructor.

……… method does not have a return type. Static. Instance. Constructor. Abstract.

Constructors are invoked using the ……… keyword when an instance is created. new. instanceof. super. this.

A public no-argument constructor is provided automatically only if no constructors are explicitly defined in the class, and in this case it is called the ……… constructor. super. final. default. abstract.

The ……… visibility modifier allows classes, methods, and data fields to be accessible by any class in the same package only. Public. Default. Protected. Private.

the keyword ------- to enable a constructor to invoke another constructor of the same class. Super. This. New. Instanceof.

the BigInteger and BigDecimal classes are imported fro use from --------- package. java.lang. java.util. java.math. javafx.java.

If a method has the public visibility modifier in a superclass then its overridden version in the subclass must have the ……… visibility modifier. public. protected. default. private.

The ……….. can be used to represent integers of any size. int primitive type. long primitive type. Integer wrapper class. BigInteger class.

The ……… package is imported by default in any java project. java.lang. java.util. java.math. javafx.geometry.

In OOP, the ………. relationship allows you to define new classes from existing classes. association. aggregation. inheritance. composition.

When multiple methods have the same name but different signatures, this is method. overriding. overloading. encapsulation. abstraction.

To prevent a class from being extended, it should be defined as ………. abstract. static. final. private.

Constructor in an abstract class is defined as ……… because it is used only by subclasses. private. protected. default. public.

Defining data fields of a class as private is known in OOP as the concept of data ………. encapsulation. inheritance. polymorphism. abstraction.

Anonymous object is an object without a name. True. False.

It is not necessary that a Java program contain a main class. True. False.