MagicSquare.java

public class MagicSquare {

	/* fields */
	public int square[][];

	/* constructor */
	public MagicSquare(int size) {
		this.square = new int[size][size];
		for (int i = 0; i < square.length; i++)
			for (int j = 0; j < square.length; j++)
				this.square[i][j] = 0;
	}

	/* public methods */
	public void fillSquare() {
		int value = 1;
		int x = this.square.length / 2;
		int y = 0;

		while (this.square[x][y] == 0) {
			// System.out.println(value);

			this.square[x][y] = value;

			x = (x + 1) % this.square.length;
			y = y == 0 ? this.square.length - 1 : y - 1;

			if (this.square[x][y] != 0) {
				x = x == 0 ? this.square.length - 1 : x - 1;
				y = (y + 2) % this.square.length;
			}

			value++;
		}
	}

	public String toString() {
		String str = "";

		for (int i = 0; i < square.length; i++) {
			for (int j = 0; j < square.length; j++)
				if (square[j][i] < 10)
					str += "  " + square[j][i];
				else
					str += " " + square[j][i];
			str += "\n";
		}

		return str;
	}

}

Main.java

public class Main {

	public static void main(String args[]) {
		MagicSquare square = new MagicSquare(7);
		square.fillSquare();
		System.out.println(square.toString());
	}

}