Chapter 11: Inheritance & Polymorphism

A final class can have instances. a. true b. false

A

Encapsulation means ______________. A. that data fields should be declared private B. that a class can extend another class C. that a variable of supertype can refer to a subtype object D. that a class can contain another class

A

Every class has a toString() method and an equals() method. a. true b. false

A

Given two reference variables t1 and t2, if t1 == t2 is true, t1.equals(t2) must be ___________. A. true B. false

A

If a method is declared private in the superclass, you may declare the method public in the subclass. a. true b. false

A

If a method is declared protected in the superclass, you may declare the method public in the subclass. a. true b. false

A

If a parameter is of the java.lang.Object type, you can pass any object to it. This is known as generic programming. a. true b. false

A

If an object is an instance of class A, and class A is a subclass of class B, then the object is also an instance of class B. a. true b. false

A

In OOP, you declare a data fields to be private. This is called_____. a. encapsulation b. inheritance c. polymorphism d. abstraction

A

Normally you depend on the JVM to perform garbage collectionautomatically. However, you can explicitly use ____ to request garbage collection. a. System.gc() b. System.exit() c. System.exit(0) d. System.gc(0)

A

The UML uses _______ before a member name to indicate that the member is public. a. + b. - c. # d. ?

A

The instanceof operator is used to determine whether an object is an instance of a certain class. a. true b. false

A

The set of all instances of a subclass is a subset of the instances of its superclass. a. true b. false

A

You can always successfully cast a subclass to a superclass. a. true b. false

A

You can use the operator == to check whether two variables refer to the same object, and use the equals() method to check the equality of contents of the two objects. a. true b. false

A

____________ can search in an unsorted list. a. Linear search b. Binary search

A

An interface can be a separate unit and can be compiled into a bytecode file. a. true b. false

A Explanation: An interface can be a separate unit and can be compiled into a bytecode file. In Java, an interface is a type that defines a set of abstract methods that a class must implement in order to fulfill a certain contract. An interface can be declared in its own file, just like a class, and can be compiled into a separate bytecode file. In object-oriented programming, interfaces are an important tool for achieving abstraction and modularity, as they allow developers to define a common set of behaviors that can be implemented by multiple classes. By separating the interface from the implementation, developers can work independently on different parts of the system without worrying about the details of each other's code.

The order in which modifiers appear before a class or a method is important. a. true b. false

A Explanation: However, it is recommended to follow a standard order for better readability and consistency in your code. The order in which modifiers appear before a class or a method can affect the accessibility and behavior of the class or method. For example, the order of the "public" and "static" modifiers can change the way the method can be accessed or called. Therefore, it is important to pay attention to the order of modifiers when defining classes and methods.The order of modifiers (such as public, private, static, etc.) before a class or a method is not important. Java allows any order for these modifiers, and they will not affect the functionality or behavior of the class or method.

Which of the following is incorrect? A. A constructor may be static. B. A constructor may be private. C. A constructor may invoke a static method. D. A constructor may invoke an overloaded constructor. E. A constructor invokes its superclass no-arg constructor by default if a constructor does not invoke an overloaded constructor or its superclass?s constructor.

A Explanation: A constructor cannot be static, because you use a constructor to create a specific instance. A constructor may be private. In this case, the use cannot create an instance using this constructor. For example, the constructor in the Math class is private. A constructor may invoke a static method just like any method can invoke a static method. A constructor can invoke an overloaded constructor using the this keyword. So, the correct answer is A.

Analyze the following code. // Program 1 public class Test { public static void main(String[] args) { Object a1 = new A(); Object a2 = new A(); System.out.println(((A)a1).equals((A)a2)); } } class A { int x; public boolean equals(A a) { return this.x == a.x; } } // Program 2 public class Test { public static void main(String[] args) { A a1 = new A(); A a2 = new A(); System.out.println(a1.equals(a2)); } } class A { int x; public boolean equals(A a) { return this.x == a.x; } } A. Program 1 displays true and Program 2 displays true B. Program 1 displays false and Program 2 displays true C. Program 1 displays true and Program 2 displays false D. Program 1 displays false and Program 2 displays false

A Explanation: In Program 1, ((A)a1).equals((A)a2) matches the equals(A a) method in the class A.

What is the output of the following code? public class Test { public static void main(String[] args) { new Person().printPerson(); new Student().printPerson(); } } class Student extends Person { private String getInfo() { return "Student"; } } class Person { private String getInfo() { return "Person"; } public void printPerson() { System.out.println(getInfo()); } } A. Person Person B. Person Student C. Stduent Student D. Student Person

A Explanation: Note that the getInfo method is private in Person. It is not known to the outside of the class. This is the method invoked from the printPerson() method.

Which statements are most accurate regarding the following classes? class A { private int i; protected int j; } class B extends A { private int k; protected int m; } A. An object of B contains data fields i, j, k, m. B. An object of B contains data fields j, k, m. C. An object of B contains data fields j, m. D. An object of B contains data fields k, m.

A Explanation: The data fields in a superclass are contained in a subclass. Whether the data fields in a superclass can be accessed in a subclass is a visibility issue. A private data field in a superclass cannot be directly accessed in a subclass, but the data field may have the getter or setter methods, which can be used to get or set a data field value.

Assume Cylinder is a subtype of Circle. Analyze the following code: Circle c = new Circle (5); Cylinder c = cy; A. The code has a compile error. B. The code has a runtime error. C. The code is fine.

A Explanation: You cannot assign a variable of a supertype to a subtype without explicit casting.

What is the output of the following code: public class Test { public static void main(String[] args) { Object o1 = new Object(); Object o2 = new Object(); System.out.print((o1 == o2) + " " + (o1.equals(o2))); } } A. false false B. true true C. false true D. true false

A Explanation: o1 == o2 is false, since o1 and o2 are two different objects. o1.equals(o2) is false since the equals method returns o1 == o2 in the Object class.

If a method is declared private in the superclass, you may declare the method protected in the subclass. a. true b. false

A The method in superclass cannot be accessed directly from the subclass

Which of the following statements are true? A. Override the methods equals and toString defined in the Object class whenever possible. B. Override the hashCode method whenever the equals method is overridden. By contract, two equal objects must have the same hash code. C. A public default no-arg constructor is assumed if no constructors are defined explicitly. D. You should follow standard Java programming style and naming conventions. Choose informative names for classes, data fields, and methods.

A, B, C, D hashCode() returns an integer representing the current instance of the class. We should calculate this value consistent with the definition of equality for the class. Thus, if we override the equals() method, we also have to override hashCode(). Whenever it(hashcode) is invoked on the same object more than once during an execution of a Java application, the hashCode method must consistently return the same integer, provided no information used in equals comparisons on the object is modified. This integer need not remain consistent from one execution of an application to another execution of the same application. If two objects are equal according to the equals(Object) method, then calling the hashCode method on each of the two objects must produce the same integer result. It is not required that if two objects are unequal according to the equals(java.lang.Object) method, then calling the hashCode method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hashtables.

Which of the following statements is true? A. You can always pass an instance of a subclass to a parameter of its superclass type. This feature is known as polymorphism. B. The compiler finds a matching method according to parameter type, number of parameters, and order of the parameters at compile time. C. A method may be implemented in several subclasses. The Java Virtual Machine dynamically binds the implementation of the method at runtime. D. Dynamic binding can apply to static methods. E. Dynamic binding can apply to instance methods.

A, B, C, E Explanation: Dynamic binding is applied to instance methods, not static methods. Static methods are bound in the compile time.

Suppose ArrayList x contains two strings [Beijing, Singapore]. Which of the following method will cause the list to become [Beijing]? A. x.remove("Singapore") B. x.remove(0) C. x.remove(1) D. x.remove(2)

A, C

Analyze the following code: ArrayList<String> list = new ArrayList<String(); list.add("Beijing"); list.add("Tokyo"); list.add("Shanghai"); list.set(3, "Hong Kong"); A. The last line in the code causes a runtime error because there is no element at index 3 in the array list. B. The last line in the code has a compile error because there is no element at index 3 in the array list. C. If you replace the last line by list.add(3, "Hong Kong"), the code will compile and run fine. D. If you replace the last line by list.add(4, "Hong Kong"), the code will compile and run fine.

A, C Explanation: There is no element at index 3.

Which of the following statements are true? A. A method can be overloaded in the same class. B. A method can be overridden in the same class. C. If a method overloads another method, these two methods must have the same signature. D. If a method overrides another method, these two methods must have the same signature. E. A method in a subclass can overload a method in the superclass.

A, D, E

If a method is declared proctected in the superclass, you may declare the method private in the subclass. a. true b. false

B

If a method is declared public in the superclass, you may declare the method private in the subclass. a. true b. false

B

In OOP, you declare a class that extends another class. This is called _____. a. encapsulation b. inheritance c. polymorphism d. abstraction

B

Inheritance means ______________. A. that data fields should be declared private B. that a class can extend another class C. that a variable of supertype can refer to a subtype object D. that a class can contain another class

B

Invoking _________ returns the first element in an ArrayList x. A. x.first() B. x.get(0) C. x.get(1) D. x.get()

B

Object-oriented programming allows you to derive new classes from existing classes. This is called ____________. A. encapsulation B. inheritance C. abstraction D. generalization

B

Superclasses contain more features than their subclasses. a. true b. false

B

Suppose an ArrayList list contains {"red", "green", "red", "green"}. What is the list after the following code?list.remove("red"); A. {"red", "green", "red", "green"} B. {"green", "red", "green"} C. {"green", "green"} D. {"red", "green", "green"}

B

The UML uses _______ before a member name to indicate that the member is private. a. + b. - c. # d. ?

B

The equals method is defined in the Object class. Which of the following is correct to override it in the String class? A. public boolean equals(String other) B. public boolean equals(Object other) C. public static boolean equals(String other) D. public static boolean equals(Object other)

B

The getValue() method is overridden in two ways. Which one is correct? I: public class Test { public static void main(String[] args) { A a = new A(); System.out.println(a.getValue()); } } class B { public String getValue() { return "Any object"; } } class A extends B { public Object getValue() { return "A string"; } } II: public class Test { public static void main(String[] args) { A a = new A(); System.out.println(a.getValue()); } } class B { public Object getValue() { return "Any object"; } } class A extends B { public String getValue() { return "A string"; } } A. I B. II C. Both I and II D. Neither

B

The size of ____________ can grow and shrink at runtime. a. an array b. an ArrayList

B

The visibility of these modifiers increases in this order: A. private, protected, none (if no modifier is used), and public. B. private, none (if no modifier is used), protected, and public. C. none (if no modifier is used), private, protected, and public. D. none (if no modifier is used), protected, private, and public.

B

What is the output of the following code? public class Test { public static void main(String[] args) { new Person().printPerson(); new Student().printPerson(); } } class Student extends Person { @Override public String getInfo() { return "Student"; } } class Person { public String getInfo() { return "Person"; } public void printPerson() { System.out.println(getInfo()); } } A. Person Person B. Person Student C. Stduent Student D. Student Person

B

Which statements are most accurate regarding the following classes? class A { private int i; protected int j; } class B extends A { private int k; protected int m; // some methods omitted } A. In the class B, an instance method can only access i, j, k, m. B. In the class B, an instance method can only access j, k, m. C. In the class B, an instance method can only access j, m. D. In the class B, an instance method can only access k, m.

B

You can always successfully cast a superclass to a subclass. a. true b. false

B

Which of the following are Java keywords? A. instanceOf B. instanceof C. cast D. casting

B Explanation: A simple rule: the keywords are all in lowercase.

Suppose an ArrayList list contains {"red", "red", "green"}. What is the list after the following code? String element = "red"; for (int i = 0; i < list.size(); i++) if (list.get(i).equals(element)) list.remove(element); A. {"red", "red", "green"} B. {"red", "green"} C. {"green"} D. {}

B Explanation: After the first loop, the list = {"red", "green"} i = 1 -> get(i) = "green" and checking this with "red" Then, out of the loop since i = 2 < list.size (at this time is 2)

Given the following classes and their objects: class C1 { }; class C2 extends C1 { }; class C3 extends C1 { }; C2 c2 = new C2(); C3 c3 = new C3(); Analyze the following statement: c2 = (C2)((C1)c3); A. c3 is cast into c2 successfully. B. You will get a runtime error because you cannot cast objects from sibling classes. C. You will get a runtime error because the Java runtime system cannot perform multiple casting in nested form. D. The statement is correct.

B Explanation: Casting c3 to c1 is correct (c3 is an instance of C1). But C1 is not an instance

Analyze the following code. // Program 1: public class Test { public static void main(String[] args) { Object a1 = new A(); Object a2 = new A(); System.out.println(a1.equals(a2)); } } class A { int x; public boolean equals(Object a) { return this.x == ((A)a).x; } } // Program 2: public class Test { public static void main(String[] args) { Object a1 = new A(); Object a2 = new A(); System.out.println(a1.equals(a2)); } } class A { int x; public boolean equals(A a) { return this.x == a.x; } } A. Program 1 displays true and Program 2 displays true B. Program 1 displays false and Program 2 displays true C. Program 1 displays true and Program 2 displays false D. Program 1 displays false and Program 2 displays false

C Explanation: In Program 1, the equals method in the Object class is overridden. a1.equals(a2) invokes this method. It returns true. In Program 2, the equals method in the Object class is not overridden. a1.equals(a2) invokes the equals method defined in the Object class, which returns false in this case.

What is the output of running class C? class A { public A() { System.out.println("The default constructor of A is invoked"); } } class B extends A { public B() { System.out.println("The default constructor of B is invoked"); } } public class C { public static void main(String[] args) { B b = new B(); } } a. Nothing displayed b. "The default constructor of B is invoked" c. "The default constructor of A is invoked" followed by "The default constructor of B is invoked" d. "The default constructor of B is invoked" followed by "The default constructor of A is invoked"e. "The default constructor of A is invoked"

C Explanation: Superclass's constructor is called before executing the statements in the subclass constructor.

Given two reference variables t1 and t2, if t1.equals(t2) is true, t1 == t2 ___________. A. is always true B. is always false C. may be true or false

C Explanation: Two different objects may be equal with the same contents.

Which of the statements regarding the super keyword is incorrect? A. You can use super to invoke a super class constructor. B. You can use super to invoke a super class method. C. You can use super.super.p to invoke a method in superclass's parent class. D. You cannot invoke a method in superclass's parent class.

C Explanation: Using super.super is not allowed in Java. So, the answer to this question is C.

Assume Cylinder is a subtype of Circle. Analyze the following code: Cylinder cy = new Cylinder(1, 1); Circle c = cy; A. The code has a compile error. B. The code has a runtime error. C. The code is fine.

C Explanation: You can assign a variable of a subtype to a supertype.

The output from the following code is __________. java.util.ArrayList<String> list = new java.util.ArrayList<String>(); list.add("New York"); java.util.ArrayList<String> list1 = list; list.add("Atlanta"); list1.add("Dallas"); System.out.println(list1); A. [New York] B. [New York, Atlanta] C. [New York, Atlanta, Dallas] D. [New York, Dallas]

C Explanation: java.util.ArrayList<String> list1 = list; -> list1 and list refer to the same object

What is the output of the following code? ArrayList<java.util.Date> list = new ArrayList<java.util.Date>(); java.util.Date d = new java.util.Date(); list.add(d); list.add(d); System.out.println((list.get(0) == list.get(1)) + " " + (list.get(0)).equals(list.get(1))); A. true false B. false true C. true true D. false false

C Explanation: list.get(0) and list.get(1) point to the same object. The equals() method of Java Date class checks if two Dates are equal, based on millisecond difference.

What is the output of the following code:public class Test {public static void main(String[] args) {String s1 = new String("Java");String s2 = new String("Java");System.out.print((s1 == s2) + " " + (s1.equals(s2)));}} A. false false B. true true C. false true D. true false

C Explanation: s1 == s2 is false, since s1 and s2 are two different objects. s1.equals(s2) is true since the equals method returns true if two strings have the same content.

Given the following code, find the compile error. public class Test { public static void main(String[] args) { m(new GraduateStudent()); m(new Student());m(new Person()); m(new Object()); } public static void m(Student x) { System.out.println(x.toString()); } } class GraduateStudent extends Student { } class Student extends Person { @Override public String toString() { return "Student"; } } class Person extends Object { @Override public String toString() { return "Person"; } } A. m(new GraduateStudent()) causes an error B. m(new Student()) causes an error C. m(new Person()) causes an error D. m(new Object()) causes an error

C, D Explanation: You cannot pass a supertype variable to a subtype without explicit casting.

Analyze the following code: public class Test { public static void main(String[] args) { Object a1 = new A(); Object a2 = new Object(); System.out.println(a1); System.out.println(a2); } } class A { int x; @Override public String toString() { return "A's x is " + x; } } A. The program cannot be compiled, because System.out.println(a1) is wrong and it should be replaced by System.out.println(a1.toString()); B. When executing System.out.println(a1), the toString() method in the Object class is invoked. C. When executing System.out.println(a2), the toString() method in the Object class is invoked. D. When executing System.out.println(a1), the toString() method in the A class is invoked.

C,D Explanation: Since a1 is an instance of A, the toString() method in the A class is invoked at runtime.

Analyze the following code: double[] array = {1, 2, 3}; ArrayList<Double> list = new ArrayList<>(Arrays.asList(array)); System.out.println(list); A. The code is correct and displays [1, 2, 3]. B. The code is correct and displays [1.0, 2.0, 3.0]. C. The code has a compile error because an integer such as 1 is automatically converted into an Integer object, but the array element type is Double. D. The code has a compile error because asList(array) requires that the array elements are objects.

D

Analyze the following code: public class Test { public static void main(String[] args) { B b = new B(); b.m(5); System.out.println("i is " + b.i); } } class A { int i; public void m(int i) { this.i = i; } } class B extends A { public void m(String s) { } } A. The program has a compile error, because m is overridden with a different signature in B. B. The program has a compile error, because b.m(5) cannot be invoked since the method m(int) is hidden in B. C. The program has a runtime error on b.i, because i is not accessible from b. D. The method m is not overridden in B. B inherits the method m from A and defines an overloaded method m in B.

D

Composition means ______________. A. that data fields should be declared private B. that a class extends another class C. that a variable of supertype refers to a subtype object D. that a class contains a data field that references another object

D

Given the following code: class C1 {} class C2 extends C1 { } class C3 extends C2 { } class C4 extends C1 {} C1 c1 = new C1(); C2 c2 = new C2(); C3 c3 = new C3(); C4 c4 = new C4(); Which of the following expressions evaluates to false? A. c1 instanceof C1 B. c2 instanceof C1 C. c3 instanceof C1 D. c4 instanceof C2

D

Invoking _________ returns the number of the elements in an ArrayList x. A. x.getSize() B. x.getLength(0) C. x.length(1) D. x.size()

D

The UML uses _______ before a member name to indicate that the member is private. a. + b. - c. # d. none (blank)

D

What modifier should you use on a class so that a class in the same package can access it but a class in a different package cannot access it? a. public b. private c. protected d. Use the default modifier.

D

Which of the following statements is false? A. A public class can be accessed by a class from a different package. B. A private method cannot be accessed by a class in a different package. C. A protected method can be accessed by a subclass in a different package. D. A method with no visibility modifier can be accessed by a class in a different package.

D

Analyze the following code: public class Test { public static void main(String[] args) { String s = new String("Welcome to Java"); Object o = s; String d = (String)o; } } A. When assigning s to o in Object o = s, a new object is created. B. When casting o to s in String d = (String)o, a new object is created. C. When casting o to s in String d = (String)o, the contents of o is changed. D. s, o, and d reference the same String object.

D Explanation: Casting object reference variable does not affect the contents of the object.

Analyze the following code: public class Test { public static void main(String[] args) { new B(); } } class A { int i = 7; public A() { setI(20); System.out.println("i from A is " + i); } public void setI(int i) { this.i = 2 * i; } } class B extends A { public B() { // System.out.println("i from B is " + i); } @Overridepublic void setI(int i) { this.i = 3 * i; } } A. The constructor of class A is not called. B. The constructor of class A is called and it displays "i from A is 7". C. The constructor of class A is called and it displays "i from A is 40". D. The constructor of class A is called and it displays "i from A is 60".

D Explanation: When invoking new B(), B's superclass A's constructor is invoked first. It invokes setI(20). The setI method in B is used because object created is new B(). The setI method in B assigns 3 * 20 to i. So it displays i from A is 60.

You can assign _________ to a variable of Object[] type. A. new char[100] B. new int[100] C. new double[100] D. new String[100] E. new java.util.Date[100]

D, E Explanation: Primitive data type array is not compatible with Object[].

Invoking _________ removes all elements in an ArrayList x. A. x.remove() B. x.clean() C. x.delete() D. x.empty() E. x.clear()

E

Which of the following statements are true? A. To override a method, the method must be defined in the subclass using the same signature and compatible return type as in its superclass. B. Overloading a method is to provide more than one method with the same name but with different signatures to distinguish them. C. It is a compile error if two methods differ only in return type in the same class. D. A private method cannot be overridden. If a method defined in a subclass is private in its superclass, the two methods are completely unrelated. E. A static method cannot be overridden. If a static method defined in the superclass is redefined in a subclass, the method defined in the superclass is hidden. F. All above

F

Analyze the following code. // Program 1: public class Test { public static void main(String[] args) { Object a1 = new A(); Object a2 = new A(); System.out.println(a1.equals(a2)); } } class A { int x; public boolean equals(A a) { return this.x == a.x; } } // Program 2: public class Test { public static void main(String[] args) { A a1 = new A(); A a2 = new A(); System.out.println(a1.equals(a2)); } } class A { int x; public boolean equals(A a) { return this.x == a.x; } } A. Program 1 displays true and Program 2 displays true B. Program 1 displays false and Program 2 displays true C. Program 1 displays true and Program 2 displays false D. Program 1 displays false and Program 2 displays false

B Explanation: In Program 1, the equals method in the Object class is invoked. In Program 2, the equals method in the class A is invoked. There are now two overloaded methods available in the class A. i.e. public boolean equals(Object a) and public boolean equals(A a). Which of the two is used by a1.equals(a2) is determined at compile time. a1.equals(a2) in Program 1 matches the equals method defined in Object and a1.equals(a2) in Program 2 matches the equals method defined in the class A.

Analyze the following code: public class Test { public static void main(String[] args) { new B(); } } class A { int i = 7; public A() { System.out.println("i from A is " + i); } public void setI(int i) { this.i = 2 * i; } } class B extends A { public B() { setI(20); // System.out.println("i from B is " + i); } @Overridepublic void setI(int i) { this.i = 3 * i; } } A. The constructor of class A is not called. B. The constructor of class A is called and it displays "i from A is 7". C. The constructor of class A is called and it displays "i from A is 40". D. The constructor of class A is called and it displays "i from A is 60".

B Explanation: When invoking new B(), B's superclass A's constructor is invoked first. So it displays i from A is 7.

Suppose you create a class Square to be a subclass of GeometricObject. Analyze the following code: class Square extends GeometricObject { double length; Square(double length) { GeometricObject(length); } } A. The program compiles fine, but you cannot create an instance of Square because the constructor does not specify the length of the Square. B. The program has a compile error because you attempted to invoke the GeometricObject class's constructor illegally. C. The program compiles fine, but it has a runtime error because of invoking the Square class's constructor illegally.

B Explanation: You have use super() or super(withapproriatearguments) to invoke a super class constructor explicitly.

What is the output of the following code? ArrayList<String> list = new ArrayList<String>(); String s1 = new String("Java"); String s2 = new String("Java"); list.add(s1); list.add(s2); System.out.println((list.get(0) == list.get(1)) + " " + (list.get(0)).equals(list.get(1))); A. true false B. false true C. true true D. false false

B Explanation: list.get(0) and list.get(1) point to two different objects with the same string contents.

Analyze the following code: public class Test extends A { public static void main(String[] args) { Test t = new Test(); t.print(); } } class A { String s; A(String s) { this.s = s; } public void print() { System.out.println(s); } } a. The program does not compile because Test does not have a default constructor Test(). b. The program has an implicit default constructor Test(), but it cannot be compiled, because its superclass does not have a default constructor. The program would compile if the constructor in the class A were removed. c. The program would compile if a default constructor A(){ } is added to class A explicitly. d. The program compiles, but it has a runtime error due to the conflict on the method name print.

B ,C

Consider the following declaration for a class A. class A { private int x; private int y; public A(int x, int y) { this.x = x; this.y = y; } } Class B is a subclass of A. Which of the following can be constructors in B? I:public B() { } II:public B(int x, int y) { super(x, y); } III:public B() { super(0, 0); } IV:public B(int x, int y) { this.x = x; this.y = y; } a. I b. II c. III d. IV

B, C

Which of the following statements are true? A. A subclass is a subset of a superclass. B. A subclass is usually extended to contain more functions and more detailed information than its superclass. C. "class A extends B" means A is a subclass of B. D. "class A extends B" means B is a subclass of A.

B, C

Suppose ArrayList x contains two strings [Beijing, Singapore]. Which of the following method will cause runtime errors? A. x.get(1) B. x.set(2, "New York"); C. x.get(2) D. x.remove(2) E. x.size()

B, C, D Explanation: There is no element at index 2.

Analyze the following code: public class A extends B { } class B { public B(String s) { } } a. The program has a compilation error because A does not have a default constructor. b. The program has a compilation error because the default constructor of A invokes the default constructor of B, but B does not have a default constructor. c. The program would compile fine if you add the following constructor into A: A(String s) { } d. The program would compile fine if you add the following constructor into A: A(String s) { super(s); }

B, D

A final class can be extended. a. true b. false

B. False

A class design requires that a particular member variable must be accessible by any subclasses of this class, but otherwise not by classes which are not members of the same package. What should be done to achieve this? A. The variable should be marked public. B. The variable should be marked private. C. The variable should be marked protected. D. The variable should have no special access modifier. E. The variable should be marked private and an accessor method provided.

C

Analyze the following code: Double[] array = {1, 2, 3}; ArrayList<Double> list = new ArrayList<>(Arrays.asList(array)); System.out.println(list); A. The code is correct and displays [1, 2, 3]. B. The code is correct and displays [1.0, 2.0, 3.0]. C. The code has a compile error because an integer such as 1 is automatically converted into an Integer object, but the array element type is Double. D. The code has a compile error because asList(array) requires that the array elements are objects.

C

Analyze the following code: double[] c = {1, 2, 3}; System.out.println(java.util.Collections.max(c)); A. The code is correct and displays 3. B. The code is correct and displays 3.0. C. The code has a compile error on Collections.max(c). c cannot be an array. D. The code has a compile error on Integer[] c = {1, 2, 3}.

C

Analyze the following code:Integer[] c = {3, 5};java.util.Collections.shuffle(c);System.out.println(java.util.Arrays.toString(c)); A. The code is correct and displays [3, 5]. B. The code is correct and displays [5, 3]. C. The code has a compile error on Collections.shuffle(c). c cannot be an array. D. The code has a compile error on Integer[] c = {3, 5}.

C

Polymorphism means ______________. a. that data fields should be declared private. b. that a class can extend another class. c. that a variable of supertype can refer to a subtype object. d. that a class can contain another class.

C

Show the output of the following code: String[] array = {"red", "green", "blue"}; ArrayList<String> list = new ArrayList<>(Arrays.asList(array)); list.add(0, "red"); System.out.println(list); A. ["red", "green", "blue", "red"] B. ["red", "green", "blue"] C. ["red", "red", "green", "blue"] D. ["red", "green", "red", "blue"]

C

Suppose ArrayList x contains two strings [Beijing, Singapore]. Which of the following methods will cause the list to become [Beijing, Chicago, Singapore]? a. x.add("Chicago") b. x.add(0, "Chicago") c. x.add(1, "Chicago") d. x.add(2, "Chicago")

C

Suppose an ArrayList list contains {"red", "red", "green"}. What is the list after the following code? String element = "red"; for (int i = list.size() - 1; i >= 0; i--) if (list.get(i).equals(element)) list.remove(element); A. {"red", "red", "green"} B. {"red", "green"} C. {"green"} D. {}

C

Suppose an ArrayList list contains {"red", "red", "green"}. What is the list after the following code? String element = "red"; for (int i = 0; i < list.size(); i++) if (list.get(i).equals(element)) { list.remove(element); i--; } A. {"red", "red", "green"} B. {"red", "green"} C. {"green"} D. {}

C

The UML uses _______ before a member name to indicate that the member is protected. a. + b. - c. # d. ?

C

The class Date, Calendar, and ArrayList are in the ________ package. a. java.lang b. javax.swing c. java.util

C

What modifier should you use on the members of a class so that they are not accessible to another class in a different package, but are accessible to any subclasses in any package? A. public B. private C. protected D. Use the default modifier.

C

Which of the following classes cannot be extended? A. class A { } B. class A {&nbsp;&nbsp; private A();} C. final class A { } D. class A {&nbsp;&nbsp; protected A();}

C

Which of the following methods override the toString method in theObject class? a. public void toString(String s) b. public static String toString() c. public String toString() d. public String toString(String s)

C

You can create an ArrayList using _________. A. new ArrayList[] B. new ArrayList[100] C. new ArrayList<>() D. ArrayList()

C