private void displayMiddleBorder() {
		
		System.out.print(B_HEAD);
		boolean dec = false;
		
		for (int i=0; i < this.size; i++) {
			
			int size = this.size;
			while (size > 0) {
				System.out.print("-");
				size -= (dec ? 1 : 0);
				dec=(!dec);
			}
			
			System.out.print((i < this.size-1 ? "-+" : ""));
		}
		
		System.out.println(B_TAIL);
	}