help with code

I am trying to move the O throughout the game board, then change the previously occupied space to a X. For some reason it won't add or subtract from row or col when I type in U D L or R.

Code java:

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  public static void pickMove(char[][] array){
 
    int row = 0;
    int col = 0;
 
    Scanner sc = new Scanner(System.in);
    System.out.print("Enter Move: ");
    //String letter = sc.next();
    //String letter = sc.nextLine();
 
    for(row=0; row<array.length; row++){
      for(col=0; col<array.length; col++){
 
        if (array[row][col] == 'O'){
 
          char temp = array[row][col];
 
          temp = '.';
 
          if (sc.nextLine() == "U")
            row++;
          else if (letter == "D")
            row--;
          else if (letter == "L")
            col--;
          else if( letter == "R")
            col++;
 
          array[row][col] = 'X';
 
          System.out.printf("%d %d ", row, col);
          }
 
        }
 
      }
    printBoard(array);
    }

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Quote:

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if (sc.nextLine() == "U")

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Don't use == to compare the contents of strings, use equals() instead.

Code :

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if (sc.nextLine().equals("U"))

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The thing is that == compares the values of variables or other expressions. This is fine if those variables are primitive (char, int, etc) because the value (a character, integer etc) is probably what you want to compare. But it not so good if you are comparing variables or expressions that are a reference type like String. Those variables have as their value a reference (aka pointer), and you don't mean "do these expressions point at the same object?", rather you mean "do the strings these two expressions point to consist of same sequence of characters?"

The String class - and all other classes - have an equals() method that expresses what it means for two strings to be considered "the same". String also has an equalsIgnoreCase() method that expresses an obvious variation on this theme.

== compares the references. If you want to compare the references use, == and if you want to compare the contents, use equals().