如何根据用户输入设置静态最终变量？

Question

I am trying to model the classic water jug problem in AI. I have made a class "JugsState" that stores the current state of two jugs, ie how many liter of water is in jug1 and how many liter of water in jug2. In addition, I want to store the maximum amount of water each jug can hold, which I will take from the user as input. Since this(capacity of the two jugs) will be constant throughout , I am declaring them as static final variables. But I am unable to initialize them inside the constructor. Is there any other alternative to this, which maintains the encapsulation of max_jug variables inside the class JugsState?

class JugsState
{
    private static final int max_jug1,max_jug2;
    private int jug1,jug2; //stores the current amount of water in the jugs.

    JugsState(int a1,int a2)
    {
        max_jug1 = a1;
        max_jug2 = a2;
    }
}

error: "cannot assign a value to final variable max_jug1" error: "cannot assign a value to final variable max_jug2"

Answer 1

If your class represents a jug, it should not hold information about two jugs. maxAmount or volume should be a non-static member of the class:

public class Jug {
    public final double volume;
    private double currentAmount = 0;
    public Jug(double vol) { volume = vol; }
    ...
}

Answer 2

You can't change a final variable because it is final . However, you can set it to anything you want when it is declared. You can create a static function that gets the maximum for a jar. It could be something like this, if you want to get it from System.in:

private static int getMax(){
    System.out.println("Enter the maximum for a jar:");
    Scanner in=new Scanner(System.in);
    return in.nextInt();
}

Then use

private static final int max_jug1=getMax();
private static final int max_jug2=getMax();

in place of

private static final int max_jug1, max_jug2;

That will set those variables for the rest of the time that the program runs.

Answer 3

If a variable is static , then it would be re-initialized every time the constructor is called. If it is final it can be set only once. Something close to what you described could be the following (notice the static method setMaxJug1 )

   class jug
    {
        private static int max_jug1,max_jug2;
        private int jug1,jug2; //stores the current amount of water in the jugs.
        jug(){
          // Your constructor stuff
        }
        public static void setMaxJug1(int m){
           max_jug1 = m;
        }
    }

Then in the main you can call

 jug.setMaxJug1(m);

Probably there are other ways of doing what you ask, but I tried not to change too much of your code.

Just to mention, one alternative is to have those variables not static, as in:

class jug
        {
            private final int max_jug1,max_jug2;
            private int jug1,jug2; //stores the current amount of water in the jugs.
            jug(int a1,int a2)
             {
               max_jug1 = a1;
               max_jug2 = a2;
             }   
        }

Then you could use your original constructor. However, every jug Object will have (in general) a different value for max_jug1 and max_jug2 , depending on the values ( a1,a2 ) you pass in the constructor.

The right choice depends on how you want to use jug objects.