Not so smart Tic Tac Toe implementation in Java. Has a pretty flawed AI (which also happens to rely on bruteforce.)

SmartTTT.java

import java.util.Scanner;

public class SmartTTT {
	private static int[][] t;
	private static int lx, ly;

	public static final int INFINITY = 2; // this is sad.
	
	private static char ti(int i) {
		char ret;
		switch (i) {
			case 1:
				ret = 'x';
				break;
			case -1:
				ret = 'o';
				break;
			default:
				ret = ' ';
				break;
		}

		return ret;
	}
	public static void print() {
		System.out.println(String.format(" %c | %c | %c ", ti(t[0][0]), ti(t[1][0]), ti(t[2][0])));
		System.out.println("---+---+---");
		System.out.println(String.format(" %c | %c | %c ", ti(t[0][1]), ti(t[1][1]), ti(t[2][1])));
		System.out.println("---+---+---");
		System.out.println(String.format(" %c | %c | %c ", ti(t[0][2]), ti(t[1][2]), ti(t[2][2])));
	}

	private static void printerror(int error) {
		switch (error) {
			case 1:
				System.out.println("Erro: Formato de entrada errado.");
				break;
			case 2:
				System.out.println("Erro: Casa já ocupada.");
				break;
			case 3:
				System.out.println("Erro: Casa inválida.");
				break;
			default:
				break;
		}
	}

	public static int winner(int mx, int my) {
		int i;
		
		for (i=0; i<3; i++) {
			if (t[mx][i] == 0) break;
			if (t[mx][i] != t[mx][my]) break;
			if (i == 2) return t[mx][my];
		}
		for (i=0; i<3; i++) {
			if (t[i][my] == 0) break;
			if (t[i][my] != t[mx][my]) break;
			if (i == 2) return t[mx][my];
		}
		if (mx == my) {
			for (i=0; i<3; i++) {
				if (t[i][i] == 0) break;
				if (t[i][i] != t[mx][my]) break;
				if (i == 2) return t[mx][my];
			}
		}
		else if (mx + my == 2) {
			for (i=0; i<3; i++) {
				if (t[i][2-i] == 0) break;
				if (t[i][2-i] != t[mx][my]) break;
				if (i == 2) return t[mx][my];
			}
		}

		return 0;
	}
	
	public static void FindBestMove() {
		int i, j, k, l;
		for (i=0; i<3; i++) {
			for (j=0; j<3; j++) {
				if (t[i][j] == 0) {
					t[i][j] = -1;
					if (winner(i, j) == -1) { lx = i; ly = j; return; }
					t[i][j] = 0;
				}
			}
		}
		
		for (i=0; i<3; i++) {
			for (j=0; j<3; j++) {
				if (t[i][j] == 0) {
					t[i][j] = 1;
					if (winner(i, j) == 1) { t[i][j] = -1; return; }
					t[i][j] = 0;
				}
			}
		}

		for (i=0; i<3; i++) {
			for (j=0; j<3; j++) {
				if (t[i][j] == 0) {
					t[i][j] = -1;
					
					int c = 0;
					int fk = 0;
					for (k=0; k<3; k++) {
						for (l=0; l<3; l++) {
							if (t[k][l] == -1) c++;
						}
						if (c == 2) fk++;
						c = 0;
					}
					if (fk >= 2) return;

					for (k=0; k<3; k++) {
						for (l=0; l<3; l++) {
							if (t[l][k] == -1) c++;
						}
						if (c == 2) fk++;
						c = 0;
					}
					if (fk >= 2) return;
					
					for (k=0; k<3; k++) {
						if (t[k][k] == -1) c++;
						if (c == 2) fk++;
						c = 0;
					}
					if (fk >= 2) return;

					for (k=0; k<3; k++) {
						if (t[k][2-k] == -1) c++;
						if (c == 2) fk++;
						c = 0;
					}
					if (fk >= 2) return;

					t[i][j] = 0;
				}
			}
		}
		
		// This is most likely not perfect, but it's worth the cost.
		int c = 0;
		for (i=0; i<2; i++) {
			for (j=0; j<2; j++) {
				if (t[i==1?2:0][j==1?2:0] == 1) c++;
			}
		}
		if (c >= 2) {
			if (t[1][1] == 0) { t[1][1] = -1; return; }
			else {
				for (i=0; i<2; i++) {
					for (j=0; j<2; j++) {
						if (t[i==1?2:0][j==1?2:0] == 0) {
							t[i==1?2:0][j==1?2:0] = -1;
							return;
						}
					}
				}
			}
		}

		if (t[1][1] == 0) {
			t[1][1] = -1;
			return;
		}

		for (i=0; i<2; i++) {
			for (j=0; j<2; j++) {
				if (t[i==1?2:0][j==1?2:0] == 1) {
					if (t[i==1?0:2][j==1?0:2] == 0) {
						t[i==1?0:2][j==1?0:2] = -1;
						return;
					}
				}
			}
		}

		for (i=0; i<2; i++) {
			for (j=0; j<2; j++) {
				if (t[i==1?2:0][j==1?2:0] == 0) {
					t[i==1?2:0][j==1?2:0] = -1;
					return;
				}
			}
		}

		for (i=0; i<3; i++) {
			for (j=0; j<3; j++) {
				if (t[i][j] == 0) {
					t[i][j] = -1;
					return;
				}
			}
		}
	}

	public static void main(String args[]) {
		int i, j;
		t = new int[3][3];

		for (i=0; i<3; i++) {
			for (j=0; j<3; j++) {
				t[i][j] = 0;
			}
		}

		print();
		
		int jg = 1;
		for (i=0; i<9; i++)
			System.out.println("Vez do jogador " + jg);
			
			if (/*args[1].equals("-m") || */jg == 1) {
				Scanner sc_ = new Scanner(System.in);
				String line = sc_.nextLine();
				
				int x, y;
				Scanner sc = new Scanner(line);
				if (!sc.hasNextInt()) { printerror(1); continue; }
				x = sc.nextInt();
				if (!sc.hasNextInt()) { printerror(1); continue; }
				y = sc.nextInt();
				if (sc.hasNext()) { printerror(1); continue; }

				if (x < 0 || x > 2 || y < 0 || y > 2) { printerror(3); continue; }
				if (t[x][y] != 0) { printerror(2); continue; }

				t[x][y] = jg==1 ? 1 : -1;
				lx = x; ly = y;
			}
			else {
				FindBestMove();
			}

			if (winner(lx, ly) != 0) {
				System.out.println("Vencedor: " + jg + "!");
				print();
				break;
			}
			
			jg = jg==1 ? 2 : 1;
			print();
		}
	}
}