Lecture Notes: 2D Arrays in Java

Introduction to 2D Arrays

• Definition: A two-dimensional array in Java is an array where each element is itself an array.
• Use: Useful for storing a matrix of data.

One-Dimensional Arrays Example

• String Arrays:
  • Fruits: apple, orange, banana
  • Vegetables: potato, onion, carrot
  • Meats: chicken, pork, beef, fish

Creating a Two-Dimensional Array

• Declaration: Use two sets of square brackets [][].
• Example:
  • Name: groceries
  • Structure: Each element (fruits, vegetables, meats) is an array.

Displaying Elements of a 2D Array

• For Loop: Use a loop to iterate through each element.
  • Each element is a string array.
  • Print each array to show memory addresses initially (because arrays are reference types).
• Nested Loop: To access individual elements within these arrays.
  • Inner elements are strings.
  • Use println for new lines.

Modifying 2D Arrays

• Access/Modify Elements: Use two indices [row][column].
  • Example modifications:
    • Change apple to pineapple: groceries[0][0] = "pineapple"
    • Change potato to celery: groceries[1][0] = "celery"
    • Change pork to eggs: groceries[2][1] = "eggs"

Mini Project: Phone Number Pad

• 2D Array of Characters
  • Declaration: char[][] telephone
  • Structure:
    • Row 1: 1 2 3
    • Row 2: 4 5 6
    • Row 3: 7 8 9
    • Row 4: * 0 #
• Display with Nested Loops
  • Outer loop iterates through rows (arrays of characters).
  • Inner loop iterates through characters in each row.*

Conclusion

• Summary: 2D arrays are arrays where each element is an array, useful for matrix-like data.
• Usage: Even though not used frequently, understanding them is essential.