从另一个类调用函数

Question

I'm writing a little program for a school project. The theme is "objective Coding" so there's the "main Tab" where the draw method and setup method is. In other tabs, I wrote other classes and functions.

So in the my "main Tab" there's the function void draw and it looks like this:

void draw() {               
  background();            
  h1.displayH();
  steuerungH();
  t1.displayT();
}                           

The three methods background(); , h1.displayH(); and t1.displayT(); worked without a problem. I tried writing the code like:

...
...
h1.streuerungH();
...

h1 is an object, a rectangle I try to move with the function void steuerungH(); , but there's always an error saying:

The function steuerungH() does not exist.

Im not sure what the problem exactly is, because the class in which I wrote the function void steuerungH(); looks exacltly like the others

float gravity = 0.1;
float speed = 0;

class Steuerung {

  void steuerungH(){
    if (key == UP|| key == 'w') {
      playerYPosition = playerYPosition +speed;
      speed = speed + gravity;
        if (playerYPosition >= 30); {
          speed = speed *-1;
        }
    } else if (key == DOWN ||key == 's') {
      /*Duck methode muss noch geschrieben werden*/
    } else if (key == RIGHT || key == 'd') {
      playerXPosition = playerXPosition +10;
    } else if (key == LEFT ||key == 'a') {
      playerXPosition = playerXPosition -10;
    }
  }
}

Answer 1

First of all you should think about playerXPosition and playerYPosition . Wouldn't it be better to create a class Player with the attributes playerXPosition and playerYPosition and a method streuerungH ?

class Player {

    float gravity = 0.1;
    float speed = 0;
    float playerXPosition;
    float playerYPosition;

    // [...]

    void steuerungH(){
        if (key == UP|| key == 'w') {
            playerYPosition = playerYPosition +speed;
            speed = speed + gravity;
            if (playerYPosition >= 30); {
                speed = speed *-1;
            }
        } else if (key == DOWN ||key == 's') {
            /*Duck methode muss noch geschrieben werden*/
        } else if (key == RIGHT || key == 'd') {
            playerXPosition = playerXPosition +10;
        } else if (key == LEFT ||key == 'a') {
            playerXPosition = playerXPosition -10;
        }
    }
}

---

Anyway, if you want to keep your current designe, then you have to options to solve the issue:

Create an instance of Steuerung . eg

Steuerung s = new Steuerung();

void draw() {
    // [...]

    s.streuerungH();

    // [...]
}

---

The other option is:

Since Processing provides functions in global namespace, you can turn steuerungH to a function:

float gravity = 0.1;
float speed = 0;

void steuerungH(){
    // [...]
}

void draw() {
    // [...]

    streuerungH();

    // [...]
}

Answer 2

You have to create a new Steuerung object like this

Steuerung steuerung = new Steuerung();

Then you can call the method with

steuerung.steuerungH();

When you simply do

steuerungH();

Java will be looking for a steuerungH() method in your Main class which doesn't exist and therefor throws an error.