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

Chapter 7 Check Point Questions

Section 7.2

▼7.2.1

How do you declare an array reference variable and how do you create an array?

▼7.2.2

When is the memory allocated for an array?

▼7.2.3

What is the output of the following code?

int x = 30;
int[] numbers = new int[x];
x = 60;
System.out.println("x is " + x);
System.out.println("The size of numbers is " + numbers.length);

▼7.2.4

Indicate true or false for the following statements:
(a) Every element in an array has the same type.
(b) The array size is fixed after an array reference variable is declared.
(c) The array size is fixed after it is created.
(d) The elements in an array must be of a primitive data type.

▼7.2.5

Which of the following statements are valid?

int i = new int(30);
double d[] = new double[30];
char[] r = new char(1..30);
int i[] = (3, 4, 3, 2);
float f[] = {2.3, 4.5, 6.6};
char[] c = new char();

▼7.2.6

How do you access elements in an array?

▼7.2.7

What is the array index type? What is the lowest index? What is the representation of the third element in an array named a?

▼7.2.8

Write statements to do the following:
a. Create an array to hold 10 double values.
b. Assign the value 5.5 to the last element in the array.
c. Display the sum of the first two elements.
d. Write a loop that computes the sum of all elements in the array.
e. Write a loop that finds the minimum element in the array.
f. Randomly generate an index and display the element of this index in the array.
g. Use an array initializer to create another array with the initial values 3.5, 5.5, 4.52, and 5.6.

▼7.2.9

What happens when your program attempts to access an array element with an invalid index?

▼7.2.10

Identify and fix the errors in the following code:

 1  public class Test {
 2    public static void main(String[] args) {
 3      double[100] r;
 4
 5      for (int i = 0; i < r.length(); i++);
 6        r(i) = Math.random * 100;
 7    }
 8  }

▼7.2.11

What is the output of the following code?

 1  public class Test {
 2    public static void main(String[] args) {
 3      int list[] = {1, 2, 3, 4, 5, 6};
 4      for (int i = 1; i < list.length; i++)
 5        list[i] = list[i - 1];
 6
 7      for (int i = 0; i < list.length; i++)
 8        System.out.print(list[i] + " ");
 9    }
10  }

Section 7.4

▼7.4.1

Will the program pick four random cards if you replace lines 22-27 in Listing 7.2 DeckOfCards.java with the following code?

for (int i = 0; i < 4; i++) {
  int cardNumber = (int)(Math.random() * deck.length);
  String suit = suits[cardNumber / 13]; 
  String rank = ranks[cardNumber % 13]; 
  System.out.println("Card number " + cardNumber + ": " 
    + rank + " of " + suit);
}

Section 7.5

▼7.5.1

Use the arraycopy method to copy the following array to a target array t:

int[] source = {3, 4, 5};

▼7.5.2

Once an array is created, its size cannot be changed. Does the following code resize the array?

int[] myList;
myList = new int[10];
// Sometime later you want to assign a new array to myList
myList = new int[20];

Section 7.7

▼7.7.1

Suppose the following code is written to reverse the contents in an array, explain why it is wrong. How do you fix it?

int[] list = {1, 2, 3, 5, 4};

for (int i = 0, j = list.length - 1; i < list.length; i++, j--) {
  // Swap list[i] with list[j]
  int temp = list[i];
  list[i] = list[j];
  list[j] = temp;
}

Section 7.8

▼7.8.1

True or false? When an array is passed to a method, a new array is created and passed to the method.

▼7.8.2

Show the output of the following two programs:

(a)
public class Test {
  public static void main(String[] args) {
    int number = 0;
    int[] numbers = new int[1];

    m(number, numbers);

    System.out.println("number is " + number
      + " and numbers[0] is " + numbers[0]);
  }

  public static void m(int x, int[] y) {
    x = 3;
    y[0] = 3;
  }
} 

(b)
public class Test {
  public static void main(String[] args) {
    int[] list = {1, 2, 3, 4, 5};
    reverse(list);
    for (int i = 0; i < list.length; i++)
      System.out.print(list[i] + " ");
  }

  public static void reverse(int[] list) {
    int[] newList = new int[list.length];

    for (int i = 0; i < list.length; i++)
      newList[i] = list[list.length - 1 - i];

    list = newList;
  }
}

▼7.8.3

Where are the arrays stored during execution? Show the contents of the stack and heap during and after executing displayArray, countLetters, displayCounts in Listing 7.4.

Section 7.9

▼7.9.1

What is wrong with each of the following method headers?

public static void print(String... strings, double... numbers)
public static void print(double... numbers, String name)
public static double... print(double d1, double d2)

▼7.9.2

Can you invoke the printMax method in Listing 7.5 using the following statements?

printMax(1, 2, 2, 1, 4);
printMax(new double[]{1, 2, 3});
printMax(new int[]{1, 2, 3});

Section 7.10

▼7.10.1

If high is a very large integer such as the maximum int value 2147483647, (low + high) / 2 may cause overflow. How do you fix it to avoid overflow?

▼7.10.2

Use Figure 7.9 as an example to show how to apply the binary search approach to a search for key 10 and key 12 in list {2, 4, 7, 10, 11, 45, 50, 59, 60, 66, 69, 70, 79}.

▼7.10.3

If the binary search method returns -4, is the key in the list? Where should the key be inserted if you wish to insert the key into the list?

Section 7.11

▼7.11.1

Use Figure 7.11 as an example to show how to apply the selection-sort approach to sort {3.4, 5, 3, 3.5, 2.2, 1.9, 2}.

▼7.11.2

How do you modify the selectionSort method in Listing 7.8 to sort numbers in decreasing order?

Section 7.12

▼7.12.1

What types of array can be sorted using the java.util.Arrays.sort method? Does this sort method create a new array?

▼7.12.2

To apply java.util.Arrays.binarySearch(array, key), should the array be sorted in increasing order, in decreasing order, or neither?

▼7.12.3

Show the output of the following code:

int[] list1 = {2, 4, 7, 10};
java.util.Arrays.fill(list1, 7);
System.out.println(java.util.Arrays.toString(list1));

int[] list2 = {2, 4, 7, 10};
System.out.println(java.util.Arrays.toString(list2));
System.out.print(java.util.Arrays.equals(list1, list2));

Section 7.13

▼7.13.1

This book text declares the main method as

public static void main(String[] args)

Can it be replaced by one of the following lines?

public static void main(String args[])
public static void main(String[] x)
public static void main(String x[])
static void main(String x[])

▼7.13.2

Show the output of the following program when invoked using
1. java Test I have a dream
2. java Test "1 2 3"
3. java Test

public class Test {  
  public static void main(String[] args) {
    System.out.println("Number of strings is " + args.length);
    for (int i = 0; i < args.length; i++) 
      System.out.println(args[i]);
  }
}