Reversi (Two Players) Java Program

This program does not contain AI code, I'll be adding it later. This is just a two-player Reversi game.

Reversi Tutorial (How to Play)

I found this link useful -

http://www.samsoft.org.uk/reversi/strategy.htm

It is about some general Reversi Techniques and facts and gives some idea about making a Reversi player AI.

1. Game Board is a 2D char array.
2. Point class stores cell coordinates.
3. 'W' = White, 'B' = Black
4. Black moves first.
5. gameResult() returns 1 if White wins, -1 is Black wins and 0 if it is a draw. -2 otherwise (ignored).
6. updateScores() updates WScore, BScore and remaining. (WScore = number of whites, BScore = number of blacks, remaining = unoccupied cell count).
7. getPlaceableLocations(char player, char opponent) returns a HashSet<Point> which contains the available locations for the next move for "player".
8. showPlaceableLocations(HashSet<Point> locations, char player, char opponent) displays '*' for next available moves.
9. placeMove(Point p, char player, char opponent) actually places the move on the board for "player".
10. displayBoard() just displays the board.
11. static functions twoPlayers() is for starting the game.
12. twoPlayers() handles the situation when move needs to be passed or when no more move can be made while there are empty cells remaining.

Source:

import java.util.HashSet;
import java.util.Scanner;  
import java.util.Set;

class Board{ 
    
    public class Point{
        int x, y;
        Point(int x, int y){
            this.x = x;
            this.y = y;
        }
        
        @Override
        public String toString(){
            return "["+x+", "+y+"]";
        }
        
        @Override
        public boolean equals(Object o){
            return o.hashCode()==this.hashCode();
        }

        @Override
        public int hashCode() {
            return Integer.parseInt(x+""+y);
        }
    }
    
    private final char[][] board;
    int WScore, BScore, remaining;
    private final char boardX[] = new char[]{'A','B','C','D','E','F','G','H'};
    
    public Board(){ 
        board = new char[][]{
            {'_','_','_','_','_','_','_','_',},
            {'_','_','_','_','_','_','_','_',},
            {'_','_','_','_','_','_','_','_',},
            {'_','_','_','W','B','_','_','_',},
            {'_','_','_','B','W','_','_','_',},
            {'_','_','_','_','_','_','_','_',},
            {'_','_','_','_','_','_','_','_',},
            {'_','_','_','_','_','_','_','_',},
        };  
    }
    
    private void findPlaceableLocations(char player, char opponent, HashSet<Point> placeablePositions){ 
        for(int i=0;i<8;++i){
            for(int j=0;j<8;++j){
                if(board[i][j] == opponent){
                    int I = i, J = j;  
                    if(i-1>=0 && j-1>=0 && board[i-1][j-1] == '_'){ 
                        i = i+1; j = j+1;
                        while(i<7 && j<7 && board[i][j] == opponent){i++;j++;}
                        if(i<=7 && j<=7 && board[i][j] == player) placeablePositions.add(new Point(I-1, J-1));
                    } 
                    i=I;j=J;
                    if(i-1>=0 && board[i-1][j] == '_'){
                        i = i+1;
                        while(i<7 && board[i][j] == opponent) i++;
                        if(i<=7 && board[i][j] == player) placeablePositions.add(new Point(I-1, J));
                    } 
                    i=I;
                    if(i-1>=0 && j+1<=7 && board[i-1][j+1] == '_'){
                        i = i+1; j = j-1;
                        while(i<7 && j>0 && board[i][j] == opponent){i++;j--;}
                        if(i<=7 && j>=0 && board[i][j] == player) placeablePositions.add(new Point(I-1, J+1));
                    }  
                    i=I;j=J;
                    if(j-1>=0 && board[i][j-1] == '_'){
                        j = j+1;
                        while(j<7 && board[i][j] == opponent)j++;
                        if(j<=7 && board[i][j] == player) placeablePositions.add(new Point(I, J-1));
                    }
                    j=J;
                    if(j+1<=7 && board[i][j+1] == '_'){
                        j=j-1;
                        while(j>0 && board[i][j] == opponent)j--;
                        if(j>=0 && board[i][j] == player) placeablePositions.add(new Point(I, J+1));
                    }
                    j=J;
                    if(i+1<=7 && j-1>=0 && board[i+1][j-1] == '_'){
                        i=i-1;j=j+1;
                        while(i>0 && j<7 && board[i][j] == opponent){i--;j++;}
                        if(i>=0 && j<=7 && board[i][j] == player) placeablePositions.add(new Point(I+1, J-1));
                    }
                    i=I;j=J;
                    if(i+1 <= 7 && board[i+1][j] == '_'){
                        i=i-1;
                        while(i>0 && board[i][j] == opponent) i--;
                        if(i>=0 && board[i][j] == player) placeablePositions.add(new Point(I+1, J));
                    }
                    i=I;
                    if(i+1 <= 7 && j+1 <=7 && board[i+1][j+1] == '_'){
                        i=i-1;j=j-1;
                        while(i>0 && j>0 && board[i][j] == opponent){i--;j--;}
                        if(i>=0 && j>=0 && board[i][j] == player)placeablePositions.add(new Point(I+1, J+1));
                    }
                    i=I;j=J;
                    }
                } 
        } 
    } 
    
    public void displayBoard(Board b){  
        System.out.print("\n  ");
        for(int i=0;i<8;++i)System.out.print(boardX[i]+" ");
        System.out.println();
        for(int i=0;i<8;++i){
            System.out.print((i+1)+" ");
            for(int j=0;j<8;++j)
                System.out.print(b.board[i][j]+" ");
            System.out.println();
        }
        System.out.println(); 
    }
    
    public int gameResult(Set<Point> whitePlaceableLocations, Set<Point> blackPlaceableLocations){ 
        updateScores();
        if(remaining == 0){
            if(WScore > BScore) return 1;
            else if(BScore > WScore) return -1;
            else return 0; //Draw
        }
        if(WScore==0 || BScore == 0){
            if(WScore > 0) return 1;
            else if(BScore > 0) return -1; 
        }  
        if(whitePlaceableLocations.isEmpty() && blackPlaceableLocations.isEmpty()){
            if(WScore > BScore) return 1;
            else if(BScore > WScore) return -1;
            else return 0; //Draw
        } 
        return -2;
    } 
    
    public HashSet<Point> getPlaceableLocations(char player, char opponent){ 
        HashSet<Point> placeablePositions = new HashSet<>();
        findPlaceableLocations(player, opponent, placeablePositions);
        return placeablePositions;
    }
     
    public void showPlaceableLocations(HashSet<Point> locations, char player, char opponent){
        for(Point p:locations)
            board[p.x][p.y]='*';
        displayBoard(this);
        for(Point p:locations)
            board[p.x][p.y]='_';
    }
    
    //Although we know that if W is player, O will be the opponent but still...
    public void placeMove(Point p, char player, char opponent){
        int i = p.x, j = p.y;
        board[i][j] = player; 
        int I = i, J = j;  
        
        if(i-1>=0 && j-1>=0 && board[i-1][j-1] == opponent){ 
            i = i-1; j = j-1;
            while(i>0 && j>0 && board[i][j] == opponent){i--;j--;}
            if(i>=0 && j>=0 && board[i][j] == player) {while(i!=I-1 && j!=J-1)board[++i][++j]=player;}
        } 
        i=I;j=J; 
        if(i-1>=0 && board[i-1][j] == opponent){
            i = i-1;
            while(i>0 && board[i][j] == opponent) i--;
            if(i>=0 && board[i][j] == player) {while(i!=I-1)board[++i][j]=player;}
        } 
        i=I; 
        if(i-1>=0 && j+1<=7 && board[i-1][j+1] == opponent){
            i = i-1; j = j+1;
            while(i>0 && j<7 && board[i][j] == opponent){i--;j++;}
            if(i>=0 && j<=7 && board[i][j] == player) {while(i!=I-1 && j!=J+1)board[++i][--j] = player;}
        }   
        i=I;j=J;
        if(j-1>=0 && board[i][j-1] == opponent){
            j = j-1;
            while(j>0 && board[i][j] == opponent)j--;
            if(j>=0 && board[i][j] == player) {while(j!=J-1)board[i][++j] = player;}
        }
        j=J; 
        if(j+1<=7 && board[i][j+1] == opponent){
            j=j+1;
            while(j<7 && board[i][j] == opponent)j++;
            if(j<=7 && board[i][j] == player) {while(j!=J+1)board[i][--j] = player;}
        }
        j=J; 
        if(i+1<=7 && j-1>=0 && board[i+1][j-1] == opponent){ 
            i=i+1;j=j-1;
            while(i<7 && j>0 && board[i][j] == opponent){i++;j--;}
            if(i<=7 && j>=0 && board[i][j] == player) {while(i!=I+1 && j!=J-1)board[--i][++j] = player;}
        }
        i=I;j=J; 
        if(i+1 <= 7 && board[i+1][j] == opponent){ 
            i=i+1;
            while(i<7 && board[i][j] == opponent) i++;
            if(i<=7 && board[i][j] == player) {while(i!=I+1)board[--i][j] = player;}
        }
        i=I;

        if(i+1 <= 7 && j+1 <=7 && board[i+1][j+1] == opponent){
            i=i+1;j=j+1;
            while(i<7 && j<7 && board[i][j] == opponent){i++;j++;}
            if(i<=7 && j<=7 && board[i][j] == player)while(i!=I+1 && j!=J+1)board[--i][--j] = player;}
    }  
    
    public void updateScores(){
        WScore = 0; BScore = 0; remaining = 0;
        for(int i=0;i<8;++i){
            for(int j=0;j<8;++j){
                if(board[i][j]=='W')WScore++;
                else if(board[i][j]=='B')BScore++;
                else remaining++;
            }
        }
    }
    
    public int coordinateX(char x){
        for(int i=0;i<8;++i)if(boardX[i]==Character.toLowerCase(x)||boardX[i]==Character.toUpperCase(x))return i;
        return -1; // Illegal move received
    }
} 

public class Reversi{
    public static void twoPlayers(Board b){  
        Scanner scan = new Scanner(System.in);
        Board.Point move = b.new Point(-1, -1); 
        System.out.println("Black Moves first"); 
        
        int result;
        Boolean skip;
        String input;
        
        while(true){ 
            skip = false;
            
            HashSet<Board.Point> blackPlaceableLocations = b.getPlaceableLocations('B', 'W');
            HashSet<Board.Point> whitePlaceableLocations = b.getPlaceableLocations('W', 'B');

            b.showPlaceableLocations(blackPlaceableLocations, 'B', 'W'); 
            result = b.gameResult(whitePlaceableLocations, blackPlaceableLocations);
            
            if(result == 0){System.out.println("It is a draw.");break;}
            else if(result==1){System.out.println("White wins: "+b.WScore+":"+b.BScore);break;}
            else if(result==-1){System.out.println("Black wins: "+b.BScore+":"+b.WScore);break;}

            if(blackPlaceableLocations.isEmpty()){ 
                    System.out.println("Black needs to skip... Passing to white");
                    skip = true; 
            }

            if(!skip){
                System.out.println("Place move (Black): ");
                input = scan.next();
                move.y = b.coordinateX(input.charAt(0));
                move.x = (Integer.parseInt(input.charAt(1)+"")-1); 
                
                while(!blackPlaceableLocations.contains(move)){
                    System.out.println("Invalid move!\n\nPlace move (Black): ");
                    input = scan.next();
                    move.y = b.coordinateX(input.charAt(0)); 
                    move.x = Integer.parseInt((input.charAt(1)+""))-1;  
                }
                b.placeMove(move, 'B', 'W');
                b.updateScores();
                System.out.println("\nBlack: "+b.BScore+" White: "+b.WScore);
            }
            skip = false;

            whitePlaceableLocations = b.getPlaceableLocations('W', 'B');
            blackPlaceableLocations = b.getPlaceableLocations('B', 'W');

            b.showPlaceableLocations(whitePlaceableLocations, 'W', 'B');
            result = b.gameResult(whitePlaceableLocations, blackPlaceableLocations);

            if(result==0){System.out.println("It is a draw.");break;} 
            else if(result==1){System.out.println("White wins: "+b.WScore+":"+b.BScore);break;}
            else if(result==-1){System.out.println("Black wins: "+b.BScore+":"+b.WScore);break;}

            if(whitePlaceableLocations.isEmpty()){  
                    System.out.println("White needs to skip... Passing to Black");
                    skip = true; 
            }

            if(!skip){ 
            System.out.println("Place move (White): ");
            input = scan.next();
            move.y = b.coordinateX(input.charAt(0));
            move.x = (Integer.parseInt(input.charAt(1)+"")-1);

            while(!whitePlaceableLocations.contains(move)){
                System.out.println("Invalid move!\n\nPlace move (White): ");
                input = scan.next();
                move.y = b.coordinateX(input.charAt(0));
                move.x = (Integer.parseInt(input.charAt(1)+"")-1);
            }  
            b.placeMove(move, 'W', 'B');   
            b.updateScores();
            System.out.println("\nWhite: "+b.WScore+" Black: "+b.BScore);
            }
        }
    }
        
    public static void main(String[] args){
        Board b = new Board(); 
        twoPlayers(b); 
    }
}
 

Output:

Black Moves first

  A B C D E F G H
1 _ _ _ _ _ _ _ _
2 _ _ _ _ _ _ _ _
3 _ _ _ * _ _ _ _
4 _ _ * W B _ _ _
5 _ _ _ B W * _ _
6 _ _ _ _ * _ _ _
7 _ _ _ _ _ _ _ _
8 _ _ _ _ _ _ _ _

Place move (Black):
d3

Black: 4 White: 1

  A B C D E F G H
1 _ _ _ _ _ _ _ _
2 _ _ _ _ _ _ _ _
3 _ _ * B * _ _ _
4 _ _ _ B B _ _ _
5 _ _ * B W _ _ _
6 _ _ _ _ _ _ _ _
7 _ _ _ _ _ _ _ _
8 _ _ _ _ _ _ _ _

Place move (White):
e3

White: 3 Black: 3

  A B C D E F G H
1 _ _ _ _ _ _ _ _
2 _ _ _ _ _ * _ _
3 _ _ _ B W * _ _
4 _ _ _ B W * _ _
5 _ _ _ B W * _ _
6 _ _ _ _ _ * _ _
7 _ _ _ _ _ _ _ _
8 _ _ _ _ _ _ _ _

Place move (Black):

Skipping some output...

Place move (White):
e8

White: 14 Black: 49

  A B C D E F G H
1 B B B B B B B B
2 B B B B B B B B
3 B B B B B B B B
4 B B B B B W W B
5 B B W B B W B B
6 B B W B B W W B
7 B B W W W W B B
8 B B W * W W B B

Place move (Black):
d8

Black: 57 White: 7

  A B C D E F G H
1 B B B B B B B B
2 B B B B B B B B
3 B B B B B B B B
4 B B B B B W W B
5 B B W B B W B B
6 B B W B B B W B
7 B B B B B W B B
8 B B B B B B B B

Black wins: 57:7