Vocabulary

Array = a data structure used to implement a collection (list) of primitive or object reference data
Element = a single value in the array
Index = the position of the element in the array (starts from 0)
Array Length = the number of elements in the array
- Is public, so can be accessed in any class
- Is also final, so can’t change it after array has been created

A 2D array is an array of arrays, and can be a better way to store data
Declaring a 2D array: DataType[][] nameOf2DArray

Hack 1: Access the last element of the 2D Array list:

public class Test {

    public static void main(String[] args) {
 
      String[][] arr = {
         { "a", "f", "g" },
         { "b", "e", "h" },
         { "c", "d", "i" }
      };
 
      // Print the last element in the array!
      System.out.println("last element: "+ arr[2][2]);
       
    }
 


 }
 Test.main(null);

last element: i

Updating an element: list[r][c] = value;

Hack 2: Changing a Value:

public class Test {

    public static void main(String[] args) {
 
      String[][] arr = {
         { "Atlanta", "Baltimore", "Chicago" },
         { "Australia", "Boston", "Cincinnati" },
         { "Austin", "Beaumont", "Columbus" }
      };
 
       // Change Austin to Athens and print!
       System.out.println("Change Austin to Athens and print!");
       System.out.println(arr[arr.length - 1][arr[0].length - 3]);
       
       arr[arr.length - 1][arr[0].length - 3] = "Athens";
       System.out.println(arr[arr.length - 1][arr[0].length - 3]);


       for(int row = 0; row < arr.length; row++) {
         for(int column = 0; column < arr.length; column++) {
            System.out.print(arr[row][column] + " ");
         }
         System.out.println(" ");
      }
    }
 
 }
 Test.main(null);

Change Austin to Athens and print!
Austin
Athens
Atlanta Baltimore Chicago  
Australia Boston Cincinnati  
Athens Beaumont Columbus

You can use Nested Loops to traverse 2D Arrays

Hack 3: Unknown Dimensions:

public class Test {

   public static void main(String[] args) {
 
       String[][] arr = {
           { "Atlanta", "Baltimore", "Chicago" },
           { "Australia", "Boston", "Cincinnati" },
           { "Austin", "Beaumont", "Columbus" }
       };

       String match = "";
       String name = "Boston";
       for (String[] row : arr) {
           for (String item : row) {
               if (item.equals(name)) {
                   match = name;
               }
           }
       }

       if (match.length() == 0) {
           System.out.println("No Match!");
       } else {
           System.out.println(name);
       }
       
   }

}
Test.main(null);

Boston

Hack 4: Finding the Min/Max Value:

public class Test {

    public static void main(String[] args) {
  
        String[][] arr = {
            { "Atlanta", "Baltimore", "Chicago" },
            { "Australia", "Boston", "Cincinnati" },
            { "Austin", "Beaumont", "Columbus" }
        };

        String longest = arr[0][0];
        String shortest = arr[0][0];

        // Use nested for loops to find the longest or shortest string!
        System.out.println("Use nested for loops to find the longest or shortest string!");
        
        for(int row =0; row < arr.length; row++) {
            for(int col=0; col < arr[row].length; col++) {
                if (arr[row][col].length() > longest.length()) {
                    longest = arr[row][col];
                }
            }
        }
        
        System.out.println("Longest String: " + longest);
        
        for(int row =0; row < arr.length; row++) {
            for(int col=0; col < arr[row].length; col++) {
                if (arr[row][col].length() < shortest.length()) {
                    shortest = arr[row][col];
                }
            }
        }
        
        System.out.println("Shortest String: " + shortest);
        
    }
 
 }
Test.main(null);

Use nested for loops to find the longest or shortest string!
Longest String: Cincinnati
Shortest String: Boston

Extra submission

int height = 20;

String[][] arr = new String[height][height];

for (int col=0; col<=height; col+=2) {
    System.out.println(" ".repeat(height - col/2) +"*".repeat(col));
}

System.out.println(" ".repeat(height - 1) + "*".repeat(2));
System.out.println(" ".repeat(height - 1) + "*".repeat(2));

                    
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