I'm having trouble calling move.m_north from another function.

It is asking me to make the class move and the function m_north static, but if I do i can't reference y unless I make it static too.

I found that if y is static then any dot object I make will have the same value for y, and I need multiple dots

public class dot {
     int y=0; //<-- 3. but if I make this static then it will stay the same for every object
     public void step(int direction) {
          switch (direction){
               case 0:
                    move.m_north(); //<-- 1. is asking to make move.m_north static
          }

     }
     public class move {
          public int m_north() {
               if (y > 0) {
                    y -= 1; //<-- 2. but I need to modify and read non static variables
                    return -1;
               } else return -2;
          }
     }
}

I am able to call m_north if it is not in the move class but there are many similar functions which I believe need to be split up so I can use same names and it becomes easier to find different functions.

I would much appreciate any assistance.

CodePudding user response：

You can make this work by declaring an instance of the move class. For example (with captialization changed to match Java naming conventions):

public class Dot {
     int y=0;
     Move move = new Move();

     public void step(int direction) {
          switch (direction){
               case 0:
                    move.m_north();
          }

     }
     public class Move {
          public int m_north() {
               if (y > 0) {
                    y -= 1;
                    return -1;
               } else return -2;
          }
     }
}

Note that Move with an uppercase M is the class name, and move with a lowercase m is the name of an instance variable in the class Dot.

The reason this is required is that m_north requires an enclosing instance of Dot in order to access its y field. To put it another way, you need to call m_north on a specific dot's move instance. Making the method static doesn't provide an enclosing dot in scope.