7-6 What are the scope of variables?

A. Introduction

A method can "return" a value to the caller. Can the caller access other variables in the methods it called?

The answer is: no. This is because each variable has a scope.

B. Notes:

1. The scope of a variable is the section of a program in which the variable can be accessed (also called visible or in scope)

2. There are two types of scopes in Java

• class scope, where a variable defined in a class but not in any method

• block scope, where a variable defined in a block {} of a method; it is also called a local variable

Scoping Rules:

• local variables can be accessed ONLY in the enclosing block;

• formal arguments are valid within their methods

C. Try:

Analyze the scope of the boolean variable "win" in the main() and the checkWinner() methods below. Are they the same local variable?

import java.util.*;
class TicTacToe {
  public static void drawBoard(String board){
    System.out.println("- - - - - - -");
    System.out.println("| " + board.charAt(0) + " | " + board.charAt(1) + " | " + board.charAt(2) + " |");
    System.out.println("- - - - - - -");
    System.out.println("| " + board.charAt(3) + " | " + board.charAt(4) + " | " + board.charAt(5) + " |");
    System.out.println("- - - - - - -");
    System.out.println("| " + board.charAt(6) + " | " + board.charAt(7) + " | " + board.charAt(8) + " |");
    System.out.println("- - - - - - -");
  }
  public static String updateBoard(String board, int move, char player){
    return board.substring(0,move-1) + player + board.substring(move);
  }
  
   public static String checkWinner(String board){
    if (board.charAt(0) == board.charAt(1) && board.charAt(1) == board.charAt(2) ||
        board.charAt(3) == board.charAt(4) && board.charAt(4) == board.charAt(5) ||
        board.charAt(6) == board.charAt(7) && board.charAt(7) == board.charAt(8) || 
        board.charAt(1) == board.charAt(4) && board.charAt(4) == board.charAt(7) || 
        board.charAt(2) == board.charAt(5) && board.charAt(5) == board.charAt(8) || 
        board.charAt(0) == board.charAt(3) && board.charAt(3) == board.charAt(6) ||
        board.charAt(0) == board.charAt(4) && board.charAt(4) == board.charAt(8) || 
        board.charAt(2) == board.charAt(4) && board.charAt(4) == board.charAt(7)   ){
      boolean win = true;
      return "WIN!!";
    }
    else {
      boolean win = false;
      return "";
    }
  }
  public static String checkTie(boolean win){
    if (win == false){
      return "Sorry, this is a tie";
    }
    return "";
  }
  public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    boolean win = false;
    String board = "123456789";
    drawBoard(board);
    for (int a = 0; a < 4; a++){
      System.out.print("Player 1, enter your move (you are X): ");
      int move = in.nextInt();
      board = updateBoard(board, move, 'X');
      drawBoard(board);
      System.out.println(checkWinner(board));
      if (win == true){
        break;
      }
      System.out.println("");
      System.out.print("Player 2, enter your move (you are O): ");
      move = in.nextInt();
      board = updateBoard(board, move, 'O');
      drawBoard(board);
      System.out.println(checkWinner(board));
      if (win == true){
        break;
      }
      System.out.println("");
    }
    System.out.print("Player 2, enter your move (you are O): ");
    int move = in.nextInt();
    board = updateBoard(board, move, 'O');
    drawBoard(board);
    System.out.println(checkWinner(board));
    if (win == false){
    System.out.println(checkTie(win));
    }
  }
}