Question 1

Write code fragment to swap the two Strings stored by variables a and b.

Accepted Answer

The answer of Write code fragment to swap the two...

Question 2

Demonstrate how the following array is sorted using Selection Sort. Show the array after each pass of the outer loop.
[16, 3, 12, 13, 8, 1, 18, 9]

Accepted Answer

The answer of Demonstrate how the following array is sorted...

Question 3

So long as one is only accessing the elements of an ArrayList, its efficiency is about the same as that of an array. It's only when one begins to insert or remove elements towards the front portion of an ArrayList that its efficiency deteriorates.

Accepted Answer

ArrayLists are implemented as arrays so, as long as one is only accessing elements of an ArrayList the efficiency is about the same as for an array. But, when insertions or deletions towards the front portion of an ArrayList occur, that is when a significant amount of element copying must take place decreasing its efficiency.

Question 4

Write a method to compute the average of an int array and return the value as a double. The int array and the number of elements in the array are both passed as parameters to the method in that order.

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The answer of Write a method to compute the average...

Question 5

The length operator can be used to control a for-loop that iterates through each element of an array, as in
for (int j=0; j<list.length; j++)
However, this is not necessarily safe. Why not?

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The answer of The length operator can be used to...

Question 6

A ragged array is a multidimensional array whose initial indices don't all start at zero.

Accepted Answer

A ragged array is a multidimensional array whose lengths are not all equal. The initial index of all arrays in Java must start at zero.

Question 7

Mouse Events deal with detecting the actions of the buttons on a mouse, among other things, while Mouse Motion Events deal with the movement of the mouse with/without buttons being depressed.

Accepted Answer

Mouse Events do handle the actions of the mouse buttons. In addition, they deal with the detection of a mouse's movement onto / off of a component. Mouse Motion Events only deal with the movement of a mouse and the mouse dragging operation.

Question 8

It is possible to sort an array of int, float, double or String, but not an array of an Object class such as a CD class.

Accepted Answer

It is possible to sort any type of array as long as the type has some mechanism to compare two elements and determine their proper ordering (less than, equal, greater than). So, if the CD class has a compareTo method, then it would be possible to sort them.

Question 9

Regarding the Software Failure: In the 2003 Northeast Blackout, the backup system crashed for a different reason than the main system, which failed due to a race condition bug in the alarm system software.

Accepted Answer

Both the main system and the backup system failed for the same reason.
8.3 Free-Form Questions

Question 10

Write a method to compute and return the value of max - min where max is the largest element of an int array and min is the smallest element of an int array. The method is passed the int array and an int value that denotes the number of elements in the array. You may assume that the int array has at least 1 element in it.

Accepted Answer

The answer of Write a method to compute and return...

Question 11

Just as arrays can only have a fixed number of elements, set at the time the array is declared, a parameter list also can only have a fixed number of elements, set at the time the method is declared.

Accepted Answer

Java provides special notation for variable length parameter lists. The ellipsis (...) is used to specify a variable length parameter list.

Question 12

In Java, an array can only store one type of data. For instance, you cannot create an array that stores both double and String values.

Accepted Answer

Arrays are known as homogeneous types. This means that the type of value stored in the array must be the same for every element. The type is determined by the declaration. So, int[ ] x makes x an array of int values only. So, no array could store both doubles and Strings.

Question 13

Write a code fragment to create a two-dimensional 10x10 array and initialize every element to be the value of i * j where i and j are the two indices (for instance, element [5][3] is 5 * 3 = 15).

Accepted Answer

The answer of Write a code fragment to create a...

Question 14

An array, when instantiated, is fixed in size, but an ArrayList can dynamically change in size when new elements are added to it.

Accepted Answer

A drawback of an array is its fixed size. Once instantiated, it is fixed in size and so, if a program tries to add more elements than the size of the array, it results in an Exception being thrown. The ArrayList is a class that uses an array and automatically creates a larger array, copying the old array into the new array so that the ArrayList can be larger as needed. While this gets around the problem of a thrown Exception, it does lead to poorer performance because of having to copy from one array to another every time the ArrayList size is increased.

Question 15

The class Name consists of 4 instance data, String title, String first, String middle, String last. The class has a constructor that is passed all 4 String values and initializes the class appropriately, and has 4 methods, each returns one of the four instance data, called returnTitle( ), returnFirst( ), returnMiddle( ) and returnLast( ). Name[ ] addressBook = new Name[100]; is performed. Write a method that is passed 4 String parameters corresponding to a Name's title, first, middle, and last, and finds this Name in addressBook and returns the index of where this Name was found, or -1 if the Name was not found. Assume that addressBook stores n entries (n is an int).

Accepted Answer

The answer of The class Name consists of 4 instance...

Question 16

To swap the 3ʳᵈ and 4ᵗʰ elements in the int array values, you would do:
values[3] = values[4];
values[4] = values[3];

Accepted Answer

This code first copies values[4] into values[3] and then copies values[3] into values[4]. The result is that whatever was stored in values[4] is now stored in both values[3] and values[4]. In order to perform the swap appropriately, you would need a third variable to be used as a temporary storage location, as in
int temp = values[3];
values[3] = values[4];
values[4] = temp;

Question 17

In a two-dimensional array, both dimensions must have the same number of elements, as in[10][10].

Accepted Answer

In Java, the dimensions can have any number of positive elements, so it is possible to have a two-dimensional array with dimensions of [5] and [10].

Question 18

If the following statement is performed: CD[ ] mycollection = new CD[200]; where CD is a previously defined class, then mycollection[5] is a CD object.

Accepted Answer

The variable mycollection has been declared as an array of CD objects, so mycollection[5] is the 6ᵗʰ CD in the the array, and since a CD is an object, mycollection[5] is a CD object.

Question 19

Although methods may be declared with a variable length parameter list, class constructors cannot.

Accepted Answer

Constructors follow the same rules as normal methods do regarding how their parameter lists are declared, so they too can support variable length parameter lists.

Question 20

Demonstrate how the following array is sorted using Insertion Sort. Show the array after each pass of the outer loop.
[16, 3, 12, 13, 8, 1, 18, 9]

Accepted Answer