TTT help

[foxteknique]

My teacher gave me the basic layout for it and I have added some of my own style too it but the program is not 'smart' enough. It makes random moves - I know I need to put if/if else statements under computer moves but i don't know what to put. Help would be appreciated.

package tictactoe;

import java.util.Random;
import java.util.Scanner;

public class TicTacToe {
	private char[] cells = new char[9];
	public static char CELL_EMPTY = ' ';
	public static char CELL_CIRCLE = 'O';
	public static char CELL_CROSS = 'X';

	public TicTacToe() {
		for (int i = 0; i < cells.length; i++) {
			cells[i] = CELL_EMPTY;
		}
	}
	
	private void drawBoard() {
		System.out.println(cells[0] + " | " + cells[1] + " | " + cells[2]);
		System.out.println("- - - - -");
		System.out.println(cells[3] + " | " + cells[4] + " | " + cells[5]);
		System.out.println("- - - - -");
		System.out.println(cells[6] + " | " + cells[7] + " | " + cells[8]);
	}

	private boolean isWinner(char symbol) {
		boolean answer = false;
		if (checkRows(symbol) || checkColumns(symbol) || checkDiagnals(symbol)) {
			answer = true;
		} else {
			answer = false;
		}
		return answer;
	}
	
	public void computerMove() {
		System.out.println("======================================");
		System.out.println("Thinking . . .");
		try {
			Thread.sleep(2000);
		}
		catch (InterruptedException ie) {
		}
		System.out.println("Making move . . .");
		try {
			Thread.sleep(2000);
		}
		catch (InterruptedException ie) {
		}
		
		int emptyCellCount = 0;
		for (int i = 0; i < cells.length; i++) {
			if (cells[i] == CELL_EMPTY) {
				emptyCellCount++;
			}
		}
		
		int[] emptyCellIndexes = new int[emptyCellCount];
		emptyCellCount = 0;
		for (int i = 0; i < cells.length; i++) {
			if (cells[i] == CELL_EMPTY) {
				emptyCellIndexes[emptyCellCount] = i;
				emptyCellCount++;
			}
		}
		
		Random r = new Random();
		int randomNumber = r.nextInt(emptyCellCount);

		cells[emptyCellIndexes[randomNumber]] = CELL_CIRCLE;
		
		drawBoard();
		
		if (isWinner(CELL_CROSS)) {
			System.out.println("Congratulations! You won.");
		} else if (isWinner(CELL_CIRCLE)) {
			System.out.println("Sorry! You lost.");
		} else if (isFull()) {
			System.out.println("It's a tie!");
		} else {
			humanMove();
		}		
	}
	
	public void humanMove() {
		System.out.println("======================================");
		drawBoard();
		Scanner input = new Scanner(System.in);
		int rowNumber = 0, colNumber = 0, index = 0;
		try {
			Thread.sleep(1000);
		}
		catch (InterruptedException ie) {
		}
		System.out.println("You are 'X'. It's your turn. ");
		System.out.println("Tell me which cell you would like to occupy.");
		System.out.println("Which row [1 - 3]? ");
		rowNumber = input.nextInt();
		System.out.println("Which column [1 - 3]? ");
		colNumber = input.nextInt();
		index = (rowNumber - 1) * 3 + (colNumber - 1);
		while (!isInputValid(index)) {
			System.out.println("Invalid move! Tell me which cell you would like to occupy.");
			System.out.println("Which row [1 - 3]? ");
			rowNumber = input.nextInt();
			System.out.println("Which column [1 - 3]? ");
			colNumber = input.nextInt();
			index = (rowNumber - 1) * 3 + (colNumber - 1);
		}
		cells[index] = CELL_CROSS;
drawBoard();
		if (isWinner(CELL_CROSS)) {
			System.out.println("Congratulations! You won.");
			drawBoard();
		} else if (isWinner(CELL_CIRCLE)) {
			System.out.println("Sorry! You lost.");
			drawBoard();
		} else if (isFull()) {
			System.out.println("It's a tie!");
			drawBoard();
		}
		else {
			computerMove();
		}
	}
	private boolean isFull() {
		boolean answer = true;
		for (int i = 0; i < cells.length; i++) {
			if (cells[i] == CELL_EMPTY) {
				answer = false;
				break;
			}
		}
		return answer;
	}
	
	private boolean isInputValid(int index) {
		boolean answer = false;
		if (cells[index] == CELL_CIRCLE || cells[index] == CELL_CROSS) {
			answer = false;
		} else {
			answer = true;
		}
		return answer;
	}

	private boolean checkRows(char symbol) {
		boolean answer = false;
		if (cells[0] == symbol && cells[1] == symbol && cells[2] == symbol){
			answer = true;
		} else if (cells[3] == symbol && cells[4] == symbol && cells[5] == symbol) {
			answer = true;
		} else if (cells[6] == symbol && cells[7] == symbol && cells[8] == symbol) {
			answer = true;
		} else {
			answer = false;
		}
		return answer;
	}
	
	private boolean checkColumns(char symbol) {
		boolean answer = false;
		if (cells[0] == symbol && cells[3] == symbol && cells[6] == symbol){
			answer = true;
		} else if (cells[1] == symbol && cells[4] == symbol && cells[7] == symbol) {
			answer = true;
		} else if (cells[2] == symbol && cells[5] == symbol && cells[8] == symbol) {
			answer = true;
		} else {
			answer = false;
		}
		return answer;
	}
	
	private boolean checkDiagnals(char symbol) {
		boolean answer = false;
		if (cells[0] == symbol && cells[4] == symbol && cells[8] == symbol) {
			answer = true;
		} else if (cells[2] == symbol && cells[4] == symbol && cells[6] == symbol) {
			answer = true;
		} else {
			answer = false;
		}
		return answer;
	}
}

[KevinWorkman]

Well, how would you design a strategy for a human player?

[foxteknique]

you mean analyzing the input and blocking the other players 2 in a row or adding to my own 2 in a row for a win? I know what I need to do, I just don't know how to. Sorry if that was unclear in my first post.

[KevinWorkman]

That's a good place to start. So maybe write a method that detects when the player or the opponent has two in a row?

[foxteknique]

I don't know how :( That's why I'm here asking for help. I tried searching for help on this before but I couldn't find anything that gave me what I needed. Hence why I'm here.

[KevinWorkman]

Not to go in a circle, but how would a human detect two in a row?

[Fubarable]

Kevin's right: the first thing you have to do is write out the logic behind solving this without a computer. The algorithm will come from this.

[foxteknique]

I know you guys are trying to help but I'm just stuck - I have pretty basic understanding and use of Java.

[Fubarable]

I know you guys are trying to help but I'm just stuck - I have pretty basic understanding and use of Java.

We're not asking you to use Java knowledge yet. For gosh's sake, please write out the logic of the problem itself, how you'd solve it without a computer, and then post it here.