Plus Shape Star Pattern

Java 8 has no String.repeat, so we use a small helper method. In Java 11 and newer you can write "*".repeat(count).

/*
 * Problem : Plus shape of stars.
 * Input   : One odd integer n (side length of the square).
 * Output  : n lines.
 * Approach: Find the middle row and the middle column.
 * Time    : O(n^2)
 * Space   : O(1)
 * Java    : 8 or newer.
 */
import java.util.Scanner;

public class Main {
    // This method returns the text repeated "count" times. Java 11 has String.repeat for this.
static String repeat(String text, int count) {
    StringBuilder result = new StringBuilder();
    for (int i = 0; i < count; i++) {
        result.append(text);
    }
    return result.toString();
}

    public static void main(String[] args) {
        int size = new Scanner(System.in).nextInt();

        // Step 1: Find the middle index. Example: size 5 -> indexes 0..4 -> middle is 2.
        int middle = size / 2;

        // Step 2: Repeat once for each row. Row numbers start at 0.
        for (int row = 0; row < size; row++) {
            if (row == middle) {
                // Step 3: The middle row is full of stars.
                System.out.println(repeat("*", size));
            } else {
                // Step 4: Other rows have spaces and then one star in the middle column.
                System.out.println(repeat(" ", middle) + "*");
            }
        }
    }
}