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Java (Chapter 9)

Classes/Objects

QuestionAnswer
9.1 ____________ represents an entity in the real world that can be distinctly identified. An object
9.2 _____________ is a construct that defines objects of the same type. A class
9.3 An object is an instance of a _________ . class
9.4 The keyword ________ is required to declare a class. class
9.5 ___________ is invoked to create an object. A constructor
9.6 [True or False] A default constructor is provided automatically if no constructors are explicitly declared in the class. True
9.6 [T/F] At least one constructor must always be defined explicitly. False
9.6 [T/F] Every class has a default constructor. False
9.6 The default constructor is a no-arg constructor. True
9.7 [T/F] Multiple constructors can be defined in a class. True
9.7 [T/F] Constructors do not have a return type, not even void. True
9.7 [T/F] Constructors must have the same name as the class itself. True
9.7 [T/F] Constructors are invoked using the “new” operator when an object is created. True
9.12 The default value for data field of a “boolean” type, “numeric” type, “object” type is _______, respectively. false, 0, null
9.13 [T/F] Local variables do not have default values. True
9.13 [T/F] Data fields have default values. True
9.13 [T/F] A variable of a primitive type holds a value of the primitive type. True
9.13 [T/F] A variable of a reference type holds a reference to where an object is stored in the memory. True
9.13 [T/F] You may assign an int value to a reference variable. False
9.10 Explain the given the declaration of “Circle x = new Circle()”. “x” is the reference variable that can reference a “Circle” object or null if it does not reference any object.
9.17 [T/F] A reference variable is an object. False because a reference variable is not an object, it is a reference that points to an object.
9.17 [T/F] A reference variable references to an object. True
9.17 [T/F] A data field is a class must be a primitive type. False because a class may have a data field of an object type such as a String.
9.17 [T/F] A data field in a class can be of an object type. True
9.19 [T/F] When creating a Random object, you have to specify the seed or use of the default seed. A “seed” is a number used to initialize a random number generator. True
9.19 [T/F] If two Random objects have the same seed, the sequence of the random numbers obtained from these two objects are identical. True
9.19 [T/F] The “nextInt()” method in the Random class returns the next random int value. True
9.19 [T/F] The “nextDouble()” method in the Random class returns the next random double value. True
9.20 To obtain the distance between the points (40,50) and (5.5, 4.4), use ___________ . “new Point2D(40,50).distance(5.5,4.4)” or “new Point2D(40,50).distance(new Point2D(5.5,4.4))” “new Point2D(5.5,4.4).distance(40,50)” or “new Point2D(5.5,4.4).distance(new Point2D(40,50))”
9.21 Variables that are shared by every instance of a class are ______________ . class variables
9.23 A method that is associated with an individual object is called ____________ . an instance method
9.24 To declare a constant MAX_LENGTH as a member of the class, you write ____________ . “final static double MAX_LENGTH = 99.98” [A “constant” is known as a final variable and represents permanent data that never changes. The word “final” is a Java keyword for declaring a constant. Format: final data type CONSTANTNAME = value;]
9.29 Suppose the xMethod() is invoked in the following constructor in a class, xMethod() is ______ in the class. [public MyClass() { xMethod(); } ] A static method or an instance method.
9.30 Suppose the xMethod() is invoked from a main method in a class, xMethod() is ______ in the class. [public static void main(String[] args) { xMethod(); } ] a static method
9.31 To prevent a class from being instantiated, ____________ . use the private modifier on the constructor
Created by: Smurfette42
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