[java] Error: Main method not found in class Calculate, please define the main method as: public static void main(String[] args)

My suggestions :

• Keep the program modular. Keep the Calculate class in a separate Calculate.java file and create a new class that calls the main method. This would make the code readable.

• For setting the values in the number, use constructors. Do not use like the methods you have used above like :

  public void setNumber(double fnum, double snum){ this.fn = fnum; this.sn = snum; }

  Constructors exists to initialize the objects.This is their job and they are pretty good at it.

• Getters for members of Calculate class seem in place. But setters are not. Getters and setters serves as one important block in the bridge of efficient programming with java. Put setters for fnum and snum as well

• In the main class, create a Calculate object using the new operator and the constructor in place.

• Call the getAnswer() method with the created Calculate object.

Rest of the code looks fine to me. Be modular. You could read your program in a much better way.

Here is my modular piece of code. Two files : Main.java & Calculate.java

Calculate.java

public class Calculate {


private double fn;
private double sn;
private char op;

    public double getFn() {
        return fn;
    }

    public void setFn(double fn) {
        this.fn = fn;
    }

    public double getSn() {
        return sn;
    }

    public void setSn(double sn) {
        this.sn = sn;
    }

    public char getOp() {
        return op;
    }

    public void setOp(char op) {
        this.op = op;
    }



    public Calculate(double fn, double sn, char op) {
        this.fn = fn;
        this.sn = sn;
        this.op = op;
    }


public void getAnswer(){
    double ans;
    switch (getOp()){
        case '+': 
            ans = add(getFn(), getSn());
            ansOutput(ans);
            break;
        case '-': 
            ans = sub (getFn(), getSn());
            ansOutput(ans);
            break;
        case '*': 
            ans = mul (getFn(), getSn());
            ansOutput(ans);
            break;
        case '/': 
            ans = div (getFn(), getSn());
            ansOutput(ans);
            break;
        default:
            System.out.println("--------------------------");
            System.out.println("Invalid choice of operator");
            System.out.println("--------------------------");
        }
    }
    public static double add(double x,double y){
        return x + y;
    }
    public static double sub(double x, double y){
        return x - y;
    }
    public static double mul(double x, double y){
        return x * y;
    }
    public static double div(double x, double y){
        return x / y;
    }

    public static void ansOutput(double x){
        System.out.println("----------- -------");
        System.out.printf("the answer is %.2f\n", x);
        System.out.println("-------------------");
    }
}

Main.java

public class Main {
    public static void main(String args[])
    {
        Calculate obj = new Calculate(1,2,'+');
        obj.getAnswer();
    }
}