What is the meaning of local variable hides a field?

Question

So this is just a part of my code, and the entire program compiles and works, but I keep getting "local variable hides a field" next to lines three consecutive lines starting with "GameBoard myBoard = this.getGameBoard();. I'm just curious what that actually means and if it is doing anything to my program in the long run.

public void initialze(){
    myBoard = getGameBoard();
    obstacleLocations = myBoard.getObstaclePositions();
    pastureLocations = myBoard.getPasturePositions();

GameBoard myBoard = this.getGameBoard();
    ArrayList<GameLocation> obstacleLocations = myBoard.getObstaclePositions();
    ArrayList<GameLocation> pastureLocations = myBoard.getPasturePositions();
    GameLocation closestPasture = pastureLocations.get(0);
    GameLocation closestObstacle = obstacleLocations.get(0);

Answer 1

It means you've got two different variables with the same name - myBoard. One of them is a field in your class. Another one is a local variable, that is, one that you've declared inside a method.

It's a bad idea to have two variables with the same name. It can make your code very confusing and difficult to maintain.

Answer 2

The local variable in a method is always the variable with the highest visibility. That's why in a class setter you always do something like:

void setId(String id) {
    this.id = id;
}

The this.id tells Java to assign the id (from the parameter) to the field variable. That's why this will not work:

void setId(String id) {
    id = id;
}

Since it'll assign id to itself.

You can read about scope, see: http://www.java-made-easy.com/variable-scope.html for an example.