• Traversing is accessing every value in the array
  • Can be done using a loop like a for loop or while loop
  • Below is an example - using a for loop, we can iterate through each fruit in the array of Strings and print it out
// Here is the array we will be working with
String[] myFruits = new String[] {"Apple", "Strawberry", "Watermelon", "Blueberry"};

for (int i = 0; i < myFruits.length; i++) {
    System.out.println("Fruit number " + i + " is " + myFruits[i]);
}

Fruit number 0 is Apple
Fruit number 1 is Strawberry
Fruit number 2 is Watermelon
Fruit number 3 is Blueberry
  • Can also loop through an array in reverse
for (int i = myFruits.length - 1; i >= 0 ; i--) {
    System.out.println("Fruit number " + i + " is " + myFruits[i]);
}

Fruit number 3 is Blueberry
Fruit number 2 is Watermelon
Fruit number 1 is Strawberry
Fruit number 0 is Apple
  • If we have a list of numbers, we could change each value in the array by a certain amount 
// Here is the array we will be working with
int[] myNumbers = new int[] {1, 3, 5, 7, 9};

for (int i = 0; i < myNumbers.length; i++) {
    // add 10 to each element in the array
    myNumbers[i] += 10;
    System.out.println("New element " + i + " is " + myNumbers[i]);
}

New element 0 is 11
New element 1 is 13
New element 2 is 15
New element 3 is 17
New element 4 is 19
  • We can also traverse an array using a while loop
// Here is the array we will be working with
String[] myFruits = new String[] {"Apple", "Strawberry", "Watermelon", "Blueberry"};

int i = 0; 
while (i < myFruits.length) {
    System.out.println("Fruit number " + i + " is " + myFruits[i]);
    i++;
}

Fruit number 0 is Apple
Fruit number 1 is Strawberry
Fruit number 2 is Watermelon
Fruit number 3 is Blueberry

Bound Errors

  • ArrayIndexOutOfBoundsException thrown, can happen when using loops to access array elements
  • In the example below instead of the condition being while the index is less than the length of the array, the condition is less than or equal too
  • This mean the loop will try to run when i = 4 (since the length of the list is 4). However since array index starts from 0, the last item in the array will have an index of 3. So, index of 4 will be out of bounds, resulting in the error.
int i = 0; 

while (i <= myFruits.length) {
    System.out.println("Fruit number " + i + " is " + myFruits[i]);
    i++;
}

Fruit number 0 is Apple
Fruit number 1 is Strawberry
Fruit number 2 is Watermelon
Fruit number 3 is Blueberry

---------------------------------------------------------------------------
java.lang.ArrayIndexOutOfBoundsException: Index 4 out of bounds for length 4
	at .(#17:3)

Traversing Arrays Hacks

Hack 1

  • Create a function that takes in a list of integers and returns the list with the integers in ascending order. Print every element in this list
  • Example
    • int[] myNumbers = new int[] {5, 3, 4, 1, 2};
    • arraySorter(myNumbers);
    • Expected Output
      • 1
      • 2
      • 3
      • 4
      • 5

Hack 2

  • Given the following code segment, which of the following will cause an infinite loop? Assume that temp is an int variable initialized to be greater than zero and that a is an array of integers.
for ( int k = 0; k < a.length; k++ )
{
   while ( a[ k ] < temp )
   {
      a[ k ] *= 2;
   }
}
  • A. The values don't matter this will always cause an infinite loop.
  • B. Whenever a includes a value that is less than or equal to zero.
  • C. Whenever a has values larger then temp.
  • D. When all values in a are larger than temp.
  • E. Whenever a includes a value equal to temp.