How can I change a variable value in the main class from a different class?

Question

I am coding a small game for my amusement and I'm having an issue with getting a variable to be changed in one class from a value in another. I have actually done this in another class that wasn't the main. The error I am getting when running is that I need main() to be main(String[] args) which I changed to main(int wgold) .

import java.io.*;


class player {
    public static void main (String[] args) throws IOException { // <<<<<<<<<<<<<<<<<<<<< Need to have this get the value sent
        String Name, cmd;
        int gold, quit, spaces, weint, randGold;

        gold = 0;
        cmd = "none";
        quit = 0;
        spaces = 0;
        weint = 0;

        /* Ideas for new commands:
        attack - Attacks monster you have run into. - 100%
        eat - Heals you. - 0%
        run - Gets you away from a battle. - 100%
        walk - Moves you one space and you can: find something (gold, food, ect...) or run into a monster. - 50%
        */

        while (quit == 0) {
            gold += wgold; // <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< This is the setting of the gold after the battle >>>>>>>>>>>>>>>>>>>>>>>
            wgold = 0;
            if (cmd.equalsIgnoreCase("none")) {
                System.out.println("-------Commands-------\n");
                System.out.println("distance - Displays the amount of spaces you have walked.");
                System.out.println("gold - Shows the amount of gold you have.");
                System.out.println("quit - Exits the program.");
                System.out.println("walk - Moves you one space.\n");
                System.out.println("--End of command list--\n");
                cmd = "wait";
                BufferedReader stdin = new BufferedReader (new InputStreamReader (System.in));
                System.out.print("Command: ");
                System.out.flush();
                cmd = stdin.readLine();
            }

            if (cmd.equalsIgnoreCase("gold")) {
                System.out.println("\nGold: " + gold + "\n");
                cmd = "none";
            }else if (cmd.equalsIgnoreCase("walk")) {
                spaces += 1;
                weint = misc.random(1000); // Sets a random number out of 1000 for a percentage.
                if ((weint >= 0) & (weint < 300)) {
                    enemies obj = new enemies();
                    obj.main();
                    cmd = "none";
                } else if ((weint >= 300) & (weint < 500)) {
                    randGold = misc.random(10); // Sets the random amount of gold found while walking.
                    if (randGold <= 0) {
                        randGold = 1;
                    }
                    System.out.println("\nYou have walked one space and found " + randGold + " gold piece(s).\n");
                    gold += randGold;
                    cmd = "none";
                } else if ((weint >= 500) & (weint <= 1000)) {
                    System.out.println("\nYou have walked one space.\n");
                    cmd = "none";
                }
            } else if (cmd.equalsIgnoreCase("distance")) {
                System.out.println("\nSpaces you have moved: " + spaces + ".\n");
                cmd = "none";
            } else if (cmd.equalsIgnoreCase("quit")) {
            System.out.println("Quitting the program...");
            quit = 1;
            } else {
                System.out.println("\nCommand not recognized.\n");
                cmd = "none";
            }
        }
    }
}

class battle {
    public static void main(String monster, int level, int mhp, int drop) throws IOException { // (String monster) gets the return value of the monster sent by the enemies class.
        int end, hp, str, smhp, exp;
        Long hit;
        String cmd;

        end = 0;
        hp = 10;
        str = 1;
        exp = 0;
        smhp = mhp;
        cmd = "none";

        System.out.println("\n\n\n-------Battle!-------\n\n\n");
        System.out.println("You've encountered a wild " + monster + " level " + level + "!\n\n");

        while(end == 0) {
            if(cmd.equalsIgnoreCase("none")) {
                System.out.println("----Commands----\n");
                System.out.println("attack - Attacks the enemy.");
                System.out.println("run - Runs from battle.\n");
                System.out.println("--End of command list--\n\n\n");
                System.out.println("-----Status----\n");
                System.out.println("HP: " + hp + "/10");
                System.out.println("Strength: " + str + "\n");
                System.out.println("---Wild " + monster + " stats---");
                System.out.println("Wild " + monster + " HP: " + mhp + "/" + smhp + "\n");
                cmd = "wait";

                BufferedReader stdin = new BufferedReader(new InputStreamReader(System.in));
                System.out.print("Command: ");
                System.out.flush();
                cmd = stdin.readLine();
            }

            if(cmd.equalsIgnoreCase("run")) {
                System.out.println("\nYou have escaped from the battle!\n");
                end = 1;
            } else if(cmd.equalsIgnoreCase("attack")) {
                hit = Math.round(misc.random(str) * .7);

                System.out.println("You hit: " + hit);
                mhp -= hit;

                if(hit >= 1) {
                    exp += hit * 12;
                }

                cmd = "none";
                //Add HP for monsters / attack command. Not all here but you know where...
            } else {
                System.out.println("\nCommand not recognized.\n");
                cmd = "none";
            }

        if(mhp <= 0) {
            System.out.println("You have won!");
            System.out.println("You found: " + drop + " coins!");

            player obj = new player(); // <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< This is where the value is sent to the player class
            obj.main(drop);

            if(exp >= str * 80) {
                str += 1;
                System.out.println("Congradulations! You now have " + str + " strength.");
            }
            end = 1;
        }

        }
    }
}

class enemies {
    public static void main() throws IOException {
        String monster;
        int drop, level, mint, mhp;

        mint = misc.random(10);

        if (mint >= 7) {
            monster = "Goblin";
        } else {
            monster = "Wizard";
        }

        battle obj = new battle(); // calls the battle class

        level = misc.random(3); // Makes a random level for the enemy.

        mhp = level + 3;

        drop = misc.random(level);

        if(drop <= 0) {
            drop = 1;
        }

        drop = drop * 3;

        obj.main(monster, level, mhp, drop); // sends the String monster to the battle class.
    }
}

I know my code is a mess and there are probably a lot of things I could have done differently but I am just learning at the moment. Any help would be very appreciated.

This code is also available here: http://pastebin.com/kjuD3GJd

Answer 1

You need a reference to the instance to the Main class. Something along the following code scetch (will contain typos)

public class Main{
    public static void main (String[] args){
        new Main().start();
    }
    public void start(){
        new OtherClass(this).doSomething();
    }

    public void whatever(){...}
}

public class OtherClass{
    private final Main main; 
    public OtherClass(Main aMain){
        main = aMain;
    }
    public void doSomething{
        main.whatever();
    }
}

Inside the whatever method you can access all the state of the Main instance. Of course you can pass parameters as well.

Regarding your other implicit question: To start a program you have to use a static void main(String[] args) method. Anything else wont work. Of course you can have arbitrary other methods including some with the same name, although I would recommend to use unique names for starters. This avoids the compiler confusing you about which method it is complaining.

As a an add-on some advice on asking questions here: Copy(*) your code to a fresh project. Then remove everything not necessary to understand your problem. In 9 out of 10 cases you'll find the solution to your problem in the process. In the last case you have a code sample that people are actually looking at, resulting in much better answers.

(*) instead of copying the use of a version control system, eg is recommended, but I guess you are not there yet.

Answer 2

You don't need a main method for every class. You could solve the problem by renaming the method to any other thing and then calling it.

Static methods don't need an object instance:

public class MainClass {
    /* args is the array of string commands passed as arguments
       when the program is invoked */
    public static void main(String[] args) {
        MyClass objRef = new MyClass();
        System.out.println(MyClass.myStaticMethod());
        //System.out.println(MyClass.nonStaticMethod()); // Cannot access a non-static method without an instance.
        System.out.write(objRef.nonStaticMethod());
    }

}

class MyClass {
    public static int myStaticMethod() {
        return 1;
    }

    public int nonStaticMethod() {
        return 2;
    }
}

There should be only one public class per file, and this file must have the same name as the public class.