How to fill a matrix with uppercase AND lowercase characters-CodePudding

Hello and thank you for reading this. I have written code that fills a 2d triangular array, but it only fills with lower case letters. How do I get it to also fill with uppercase letters?

Here is a small part of the code:

public static void fillSpecialMatrice(char[][] matrice) {
   Random random = new Random();
   for(int i = 0; i < matrice.length; i  ) {
      for(int j = 0; j < matrice.length-i; j  ) {
         matrice[i][j] = (char) (random.nextInt(26)   'a');
      }
   }
}

How the triangular matrix looks when printed:

CodePudding user response：

You can randomize upper and lower-cases as well. Something like this:

public static void fillSpecialMatrice(char[][] matrice) {
    Random random = new Random();
        for(int i = 0; i < matrice.length; i  ) {
            for(int j = 0; j < matrice.length-i; j  ) {
                   case_int = random.nextInt(2);
                   case_char = (case_int == 0 ) ? 'a' : 'A';
                   matrice[i][j] = (char) (random.nextInt(26)   case_char);
     }
    }
  }

CodePudding user response：

ThreadLocalRandom offers methods making it more convenient than Random.

The char type has been legacy since Java 5, essentially broken since Java 2. As a 16-bit value, char is physically incapable of representing most characters. Instead, use code point integer numbers to represent individual characters.

The Character class offers static methods toUpperCase & toLowerCase. By the way, the class also offers toTitleCase; see Difference between uppercase and titlecase.

The word “matrix” is the singular of “matrices”, in English.

Putting that all together, we get code that looks like the following.

final int origin = Character.codePointAt( "a" , 0 );
final int bound = origin   26;  // Twenty-six characters in US English alphabet, in US-ASCII subset of Unicode.
final int rows = 7, columns = 7;
final String[][] matrix = new String[ rows ][ columns ];

for ( int i = 0 ; i < matrix.length ; i   )
{
    for ( int j = 0 ; j < matrix.length - i ; j   )
    {
        int codePoint = ThreadLocalRandom.current().nextInt( origin , bound );
        // Randomly use uppercase rather than default lowercase.
        if ( ThreadLocalRandom.current().nextBoolean() )
        {
            codePoint = Character.toUpperCase( codePoint );
        }
        matrix[ i ][ j ] = Character.toString( codePoint );
    }
}

Dump to console.

System.out.println( Arrays.deepToString( matrix ) );

for ( int rowIndex = 0 ; rowIndex < matrix.length ; rowIndex   )                            // Rows.
{
    for ( int columnIndex = 0 ; columnIndex < matrix[ rowIndex ].length ; columnIndex   )   // Columns
    {
        String cell = matrix[ rowIndex ][ columnIndex ];
        String output = Objects.isNull( cell ) ? " " : cell;  // Ternary operator. Effectively a compact if-else statement. 
        System.out.print( output   " " );
    }
    System.out.println();                                 // Next line.
}

When run.

[[a, P, F, B, u, R, j], [G, o, F, H, z, L, null], [N, R, f, y, m, null, null], [U, f, F, j, null, null, null], [R, G, i, null, null, null, null], [G, b, null, null, null, null, null], [g, null, null, null, null, null, null]]
a P F B u R j 
G o F H z L   
N R f y m     
U f F j       
R G i         
G b           
g