A, B, C, D, E, F, G, H in the matrix, provided that they use the letters at a maximum and a minimum of 2 times

enter image description here

like this ...

As shown in the picture, 3 letters of the same letter should be written at most and at least 2 times.

this is my pillow code part

Random r = new Random();
for (int i = 0 ; i < 4 ; i++){
    for (int j = 0 ; j < 4 ; j++){
        char c = (char)(r.nextInt(8) + 'a');
        cards[i][j] = new Card(c);
    }
}

In a 4x4 card game we were trying to find the same 2 letters written under the cards.

You don't need to use the Random class at all. As @Yunnosch mentioned in his comment, you need to create an array of letter pairs, copy the array to a java.util.List, shuffle the List, and copy the shuffled List to your matrix.

Here's the output from a test run.

[b, e, e, b]
[g, d, f, d]
[f, h, h, a]
[c, g, a, c]

Here's the code I used.

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

public class ShuffleExample {

	public static void main(String[] args) {
		char[][] cards = new char[4][4];

		char[] letters = { 'a', 'a', 'b', 'b', 'c', 'c', 'd', 'd', 
				'e', 'e', 'f', 'f', 'g', 'g', 'h', 'h' };
		List<Character> pairs = new ArrayList<>();
		
		for (int i = 0; i < letters.length; i++) {
			pairs.add(letters[i]);
		}
		
		Collections.shuffle(pairs);

		int index = 0;
		for (int i = 0; i < cards.length; i++) {
			for (int j = 0; j < cards[i].length; j++) {
				cards[i][j] = pairs.get(index++);
			}
		}

		for (int i = 0; i < cards.length; i++) {
			System.out.println(Arrays.toString(cards[i]));
		}
	}

}