For some reason I am not so fond of counters, so I did it this way (It works for boards with different sizes).
public boolean areFourConnected(int player){
// horizontalCheck
for (int j = 0; j<getHeight()-3 ; j++ ){
for (int i = 0; i<getWidth(); i++){
if (this.board[i][j] == player && this.board[i][j+1] == player && this.board[i][j+2] == player && this.board[i][j+3] == player){
return true;
}
}
}
// verticalCheck
for (int i = 0; i<getWidth()-3 ; i++ ){
for (int j = 0; j<this.getHeight(); j++){
if (this.board[i][j] == player && this.board[i+1][j] == player && this.board[i+2][j] == player && this.board[i+3][j] == player){
return true;
}
}
}
// ascendingDiagonalCheck
for (int i=3; i<getWidth(); i++){
for (int j=0; j<getHeight()-3; j++){
if (this.board[i][j] == player && this.board[i-1][j+1] == player && this.board[i-2][j+2] == player && this.board[i-3][j+3] == player)
return true;
}
}
// descendingDiagonalCheck
for (int i=3; i<getWidth(); i++){
for (int j=3; j<getHeight(); j++){
if (this.board[i][j] == player && this.board[i-1][j-1] == player && this.board[i-2][j-2] == player && this.board[i-3][j-3] == player)
return true;
}
}
return false;
}