Traversing 2D Arrays

Traversing 2D Arrays

Traversing Defined

• Traversing is the process of examining every element in an array, typically to perform a specific task or operation on each of them.

Why Traverse?

• Traversing a 2D array is important for a variety of tasks, such as searching for a specific value or modifying each value.

Nested Loop Traversal

• Nested loops are the most common way to traverse a 2D array, with an outer loop iterating over rows and an inner loop iterating over each column in a given row.
• Remember – in Java, a 2D array is essentially an array of arrays, so double iteration makes sense.

Sample Traversal Code

• A basic example might look like this:

  for(int i = 0; i < array.length; i++){
      for(int j = 0; j < array[i].length; j++){
          // Perform tasks with array[i][j] here
      }
  }
  

  This code example will iterate over every element in the 2D array.

Row-Major Versus Column-Major

• The order in which you traverse a 2D array – rows first (as above), or columns first – can matter, depending on what you need to do with the array.
• If you need to traverse column by column instead of row by row, reverse the order of your loops:

  for(int j = 0; j < array[0].length; j++){
      for(int i = 0; i < array.length; i++){
          // Perform tasks with array[i][j] here
      }
  }
  

  This will iterate over each column first before moving to the next row.

Traversal Pitfalls

• Be aware that attempting to access an element outside the bounds of a 2D array will result in an ArrayIndexOutOfBoundsException error in your code.
• Keep careful track of your index variables to ensure you do not try to access a row or column that does not exist.
• Always use array.length or array[row].length when looping over your array to avoid indexing errors.