Topics 7 & 8 - Static Methods/Variables and Null Keyword

Which of the following best describes the behavior of the code segment?

• Exactly 5 Element objects are created.

• Exactly 10 Element objects are created.

• Between 0 and 5 Element objects are created, and Element.max_value is increased only for the first object created.

• Between 1 and 5 Element objects are created, and Element.max_value is increased for every object created.

• Between 1 and 5 Element objects are created, and Element.max_value is increased for at least one object created.

Consider the following class definition.

public class WordClass

{

private final String word;

private static String max_word = "";

public WordClass (String s)

{

word = s;

if (word.length() > max_word.length())

{

max_word = word;

}

}

}

Which of the following is a true statement about the behavior of WordClass objects?

• A WordClass object can change the value of the variable word more than once.

• Every time a WordClass object is created, the max_word variable is referenced.

• Every time a WordClass object is created, the value of the max_word variable changes.

• No two WordClass objects can have their word length equal to the length of max_word.

• The value of the max_word variable cannot be changed once it has been initialized.

Consider the following class definition.

public class Something

{

private static int count = 0;

public Something()

{

count += 5;

}

public static void increment()

{

count++;

}

}

The following code segment appears in a method in a class other than Something.

Something s = new Something();

Something.increment();

Which of the following best describes the behavior of the code segment?

• The code segment does not compile because the increment method should be called on an object of the class Something, not on the class itself.

• The code segment creates a Something object s. The class Something’s static variable count is initially 0, then increased by 1.

• The code segment creates a Something object s. The class Something’s static variable count is initially 0, then increased by 5, then increased by 1.

• The code segment creates a Something object s. After executing the code segment, the object s has a count value of 1.

• The code segment creates a Something object s. After executing the code segment, the object s has a count value of 5.

Which of these should not be declared as static?

• 1. A Frog class variable that counts the number of Frog objects that have been made.

• 1. A Frog class variable that counts the number of hops a Frog object has performed.

• 1. A Frog class variable that counts the number of hops that all Frog objects have performed in total.

• A Frog class variable that counts the maximum number of total hops that any individual Frog object has performed.

A Temperature class is created that stores a double to represent a recorded temperature and another double to represent the max temperature recorded for all Temperature objects.

Identify which of the following variables and methods could be declared as static.

Variable: temperature

Variable: maxTemperature

Constructor: Temperature(double t)

Method: getTemperature()

Method: getMaxTemperature()

Method: fahrenheitToCelsius(double f)

• temperature and getTemperature

• maxTemperature and getMaxTemperature

• maxTemperature, getMaxTemperature, and fahrenheitToCelsius

• fahrenheitToCelsius

• temperature, getTemperature, and fahreheitToCelsius

The following code segment appears in a class other than Backyard. It is intended to print true if b1 and b2 have the same lengths and widths, and to print false otherwise. Assume that x, y, j, and k are properly declared and initialized variables of type int.

Backyard b1 = new Backyard(x, y);

Backyard b2 = new Backyard(j, k);

System.out.println( /* missing code */ );

Which of the following can be used as a replacement for /* missing code */ so the code segment works as intended?

Responses

• b1 == b2

• b1.equals(b2)

• equals(b1, b2)

• b1.equals(b2.getLength(), b2.getWidth())

• b1.length == b2.length && b1.width == b2.width

Which of the following can replace /* missing condition */ so that the printDetails method CANNOT cause a run-time error?

1. I. !borrower.equals(null)

2. II. borrower != null

3. III. borrower.getName() != null

• I only

• II only

• III only

• I and II

• II and III

cutFirst is intended to cut off the first letter of each element in an array of Strings, that may contain empty indexes. Which of these would fill in missing condition to ensure that no StringIndexOutOfBounds or NullPointer exceptions are thrown?

• str[i] == null || str[i].length() > 0

• str[i] != null || str[i].length() > 0

• str[i] != null && str[i].length() > 0

• str[i] == null || str[i].length() == 0