Introduction to Java Programming and Data Structures, 11E, Y. Daniel Liang

Chapter 13 Check Point Questions

Section 13.2

▼13.2.1

Which of the following classes defines a legal abstract class?

(a)
class A {    
  abstract void unfinished() { 
  }
}

(b)
public class abstract A {   
  abstract void unfinished();
} 

(c) 
public class abstract A {   
  abstract void unfinished();
} 

(d)
abstract class A {   
  protected void unfinished();
} 

(e)
abstract class A {    
  abstract void unfinished();
}

(f)
abstract class A {    
  abstract int unfinished();
}

▼13.2.2

The getArea() and getPerimeter() methods may be removed from the GeometricObject class. What are the benefits of defining getArea() and getPerimeter() as abstract methods in the GeometricObject class?

▼13.2.3

True or false?
a. An abstract class can be used just like a nonabstract class except that you cannot use the new operator to create an instance from the abstract class.
b. An abstract class can be extended.
c. A subclass of a nonabstract superclass cannot be abstract.
d. A subclass cannot override a concrete method in a superclass to define it as abstract.
e. An abstract method must be nonstatic.

Section 13.3

▼13.3.1

Why do the following two lines of code compile but cause a runtime error?

Number numberRef = new Integer(0);
Double doubleRef = (Double)numberRef;

▼13.3.2

Why do the following two lines of code compile but cause a runtime error?

Number[] numberArray = new Integer[2];
numberArray[0] = new Double(1.5);

▼13.3.3

Show the output of the following code.

public class Test {
  public static void main(String[] args) {
    Number x = 3;
    System.out.println(x.intValue());
    System.out.println(x.doubleValue());
  }
}

▼13.3.4

What is wrong in the following code? (Note that the compareTo method for the Integer and Double classes was introduced in Section 10.7.)

public class Test {
  public static void main(String[] args) {
    Number x = new Integer(3);
    System.out.println(x.intValue());
    System.out.println(x.compareTo(new Integer(4)));
  }
}

▼13.3.5

What is wrong in the following code?

public class Test {
  public static void main(String[] args) {
    Number x = new Integer(3);
    System.out.println(x.intValue());
    System.out.println((Integer)x.compareTo(new Integer(4)));
  }
}

Section 13.4

▼13.4.1

Can you create a Calendar object using the Calendar class?

▼13.4.2

Which method in the Calendar class is abstract?

▼13.4.3

How do you create a Calendar object for the current time?

▼13.4.4

For a Calendar object c, how do you get its year, month, date, hour, minute, and second?

Section 13.5

▼13.5.1

Suppose A is an interface. Can you create an instance using new A()?

▼13.5.2

Suppose A is an interface. Can you declare a reference variable x with type A like this?

A x;

▼13.5.3

Which of the following is a correct interface?

(a)
interface A {    
  void print() { }
} 

(b)      
abstract interface A {    
  abstract void print() { }
}

(c)            
abstract interface A {    
  print();
} 

(d)        
interface A {   
  void print();
}

(e)
interface A {    
  default void print() {
  }
} 

(f)
interface A {    
  static int get() {
    return 0;
  }
}

▼13.5.4

Show the error in the following code:

interface A {
  void m1();
}

class B implements A {
  void m1() {
    System.out.println("m1");
  }
}

▼13.5.5

The following questions are based on the Edible interface and the classes defined in Listing 13.7 and also assume LittleChicken is a subtype of Chicken. For each question, answer if the code can compile, can run. If not, give a reason. If it runs, give the output.

a. Edible x = new Tiger(); 

b. Edible x = new Chicken(); 
   System.out.println(x.sound()); 
	
c. Edible x = new Chicken();
   System.out.println((Animal)x.sound());	

d. Edible x = new Chicken();
   System.out.println(((Animal)x).sound());
	
e. Edible x = new LittleChicken();
   System.out.println(x.howToEat());

f. LittleChicken x = new Chicken();

Section 13.6

▼13.6.1

True or false? If a class implements Comparable, the object of the class can invoke the compareTo method.

▼13.6.2

Which of the following is the correct method header for the compareTo method in the String class?

public int compareTo(String o)
public int compareTo(Object o)

▼13.6.3

Can the following code be compiled? Why?

Integer n1 = new Integer(3);
Object n2 = new Integer(4);
System.out.println(n1.compareTo(n2));

▼13.6.4

You can define the compareTo method in a class without implementing the Comparable interface. What are the benefits of implementing the Comparable interface?

▼13.6.5

What is wrong in the following code?

public class Test {
  public static void main(String[] args) {
    Person[] persons = {new Person(3), new Person(4), new Person(1)};
    java.util.Arrays.sort(persons);
  }
}

class Person {
  private int id;

  Person(int id) {
    this.id = id;         
  }
}

▼13.6.6

Simplify the code in lines 10-15 in Listing 13.9 using one line of code. Also override the equals method in this class.

▼13.6.7

Listing 13.5 has an error. If you add list.add(new BigInteger("3432323234344343102")); in line 11, you will see that the result is incorrect. This is due to the fact that a double value can have up to 17 significant digits. When invoking doubleValue() on a BigInteger object in line 24, precision is lost. Fix the error by converting the numbers into BigDecimal and compare them using the compareTo method in line 24.

Section 13.7

▼13.7.1

Can a class invoke super.clone() when implementing the clone() method if the class does not implement java.lang.Cloneable? Does the Date class implement Cloneable?

▼13.7.2

What would happen if the House class (defined in Listing 13.11) did not override the clone() method or if House did not implement java.lang.Cloneable?

▼13.7.3

Show the output of the following code:

java.util.Date date = new java.util.Date();
java.util.Date date1 = date;
java.util.Date date2 = (java.util.Date)(date.clone());
System.out.println(date == date1);
System.out.println(date == date2);
System.out.println(date.equals(date2));

▼13.7.4

Show the output of the following code:

ArrayList<String> list = new ArrayList<>();
list.add("New York"); 
ArrayList<String> list1 = list;
ArrayList<String> list2 = (ArrayList<String>)(list.clone());
list.add("Atlanta"); 
System.out.println(list == list1);
System.out.println(list == list2);
System.out.println("list is " + list);
System.out.println("list1 is " + list1);
System.out.println("list2.get(0) is " + list2.get(0));
System.out.println("list2.size() is " + list2.size());

▼13.7.5

What is wrong in the code in (a)? Why does the code in (b) have no compile errors?

(a)
public class Test {
  public static void main(String[] args) {
    GeometricObject x = new Circle(3);
    GeometricObject y = x.clone();
    System.out.println(x == y);
  }
}

(b)
public class Test5 {
  public static void main(String[] args) throws CloneNotSupportedException {
    Test5 x = new Test5();
    GeometricObject y = (GeometricObject)x.clone();
  }
}

▼13.7.6

Show the output of the following code.

public class Test {
  public static void main(String[] args) {
    House house1 = new House(1, 1750, 50);
    House house2 = (House)house1.clone();  
    System.out.println(house1.equals(house2);
  }
}

Section 13.8

▼13.8.1

Give an example to show why interfaces are preferred over abstract classes.

▼13.8.2

Define the terms abstract classes and interfaces. What are the similarities and differences between abstract classes and interfaces?

▼13.8.3

True or false?
a. An interface is compiled into a separate bytecode file.
b. An interface can have static methods.
c. An interface can extend one or more interfaces.
d. An interface can extend an abstract class.
e. An interface can have default methods.

Section 13.9

▼13.9.1

Show the output of the following code?

Rational r1 = new Rational(-2, 6);
System.out.println(r1.getNumerator());
System.out.println(r1.getDenominator());
System.out.println(r1.intValue());
System.out.println(r1.doubleValue());

▼13.9.2

Why is the following code wrong?

Rational r1 = new Rational(-2, 6);
Object r2 = new Rational(1, 45);
System.out.println(r2.compareTo(r1));

▼13.9.3

Why is the following code wrong?

Object r1 = new Rational(-2, 6);
Rational r2 = new Rational(1, 45);
System.out.println(r2.compareTo(r1));

▼13.9.4

Simplify the code in lines 82-85 in Listing 13.13 Rational.java using one line of code without using the if statement. Simply the code in lines 110-115 using a conditional operator.

▼13.9.5

Trace the program carefully and show the output of the following code.

Rational r1 = new Rational(1, 2);
Rational r2 = new Rational(1, -2);
System.out.println(r1.add(r2));

▼13.9.6

The preceding question shows a bug in the toString method. Revise the toString() method to fix the error.

▼13.9.7

What happens if you create a Rational using new Rational(1, 0)? Discuss the appropriate ways for handling this case.

Section 13.10

▼13.10.1

Describe class design guidelines.