如何将更新的全局类变量从一种方法传递到另一种方法？

Question

I update a variable (which is global in the class) in one method and I cannot seem to be able to then pass that updated variable into another method. Any help would be appreciated, thank you. Here's my shortened code:

public class Game{

    private int randomIndexX;

    protected String spawn(){
        randomIndexX = randomGenerator.nextInt(10);
        return null;
    }

    protected String test(){
        System.out.println(this.randomIndexX);
        return null;
    }
}


public class Player extends Game{
    protected String getNextAction(String command) {
        switch(command){
            case "test":
                test();
                break;
        }
    }
}


public static void main(String[] args) {
    Game game = new Game();
    Player player = new Player();

    game.spawn();
    player.getInputFromConsole();
}

EDIT: so when i call test() from the Player class i want it to print out randomIndexX but it still doesn't seem to be working even with this.randomIndexX in the method test()

Answer 1

The first problem I can see is that you don't have a constructor.(Optional) (If you don't make one the compiler makes what is called a "Default" constructor which is a constructor without any parameters. Its usually good practice to explicitly create a class constructor.

The second problem I can see is that you missing the end bracket. Fix shown below.

public class Game

{

private int randomIndexX;

protected String spawn()
{
    randomIndexX = 0;
    return null;
}

protected String test()
{
    System.out.println(randomIndexX);
    return null;
}

}

You can construct it and trigger any methods you wish:

Game game = new Game();
game.spawn();
game.test()

Answer 2

EDIT: so when i call test() from the Player class i want it to print out randomIndexX but it still doesn't seem to be working even with this.randomIndexX in the method test().

So test() is instance method, which means you'll have to make an instance of Class Game in order to call that method, your randomIndexX is instance member so you need to think well what you want to do, IF randomIndexX is common for all the objects of Game class, you should declare it static as in:

private static in randomIndexX;

As it's value won't change depending on an object instance.

So in order to access that variable from outside of the class since it's private you declare a public method to retrieve that value (getter or also known as accessor):

public static int getRandomIndex(){
    return randomIndexX;
}

So when in main, you don't even have to make an instance of the Game class to access value that's being held in randomIndexX, you just call the getter method like this:

System.out.println(Game.getRandomIndex());

The line above will print 0 to the console as 0 is default value for members of type int, now if you want to be able to change it, you just make a setter or mutator method in Game class as well:

public static void setRandomIndex(int n){
   randomIndexX = n;
}

And there you go, you can now set and retrieve "randomIndexX" field from outside of the Game class.

For example, the code below will set value of randomIndexX to 5 and then print it in the console:

Game.setRandomIndex(5);
System.out.println(Game.getRandomIndex());