錯誤：找不到符號

Question

感謝您抽出寶貴的時間來查看此內容，到目前為止，我已經嘗試了我所知道的所有內容，並且在main（類Test）的第7、10、13和16行繼續遇到相同的錯誤。

public class Test
{
    public static void main (String[] args)
    {
        int res;

        res = new Calculadora.doAdd();
        System.out.println("The addition is: "+ res);

        res = new Calculadora.doMul ();
        System.out.println("\n The multiplication is: "+ res);

        res = new Calculadora.doDiv ();
        System.out.println("\n The division is:  "+ res);

        res = new Calculadora.doSub ();
        System.out.println("The substraction is: "+ res);

        Calculadora obj1 = new Calculadora ();
        Calculadora obj2 = new Calculadora ();
        Calculadora.contar();
        Calculadora.contar();
        System.out.println("Obj1: "+obj1.cont + " \nObj2: "+ obj2.cont);
    }
}//fin del main

第二個程序：

public class Calculadora
{
    public Addition add;
    public Substraction sub;
    public Multiplication mul;
    public Division div;

    static int cont = 0;

    static void contar()
    {
        cont++;
    }

    public Calculadora ()
    {
        add = new Addition();
        sub = new Substraction();
        mul = new Multiplication();
        div = new Division();
    }

    public int doAdd ()
    {
        return add.doAdd ();
    }

    public int doSub ()
    {
        return sub.doSub ();
    }

    public int doMul ()
    {
        return mul.doMul ();
    }

    public int doDiv ()
    {
        return div.doDiv ();
    }
}

具有操作屬性的操作程序：

public class Opperation 
{
    public int a, b;

    public Opperation ()
    {
        a = 1;
        b = 2;
    }
}

最后，操作相當簡單。

public class Substraction extends Opperation //Substraction
{
    public int doSub ()
    {
        return a-b;
    }
}//substraction

public class Multiplication extends Opperation //Multiplication
{   
    public int doMul ()
    {
        return a*b;
    }
}//Multiplication

public class Division extends Opperation //Division
{
    public int doDiv ()
    {
        return a/b;
    }
}//Division

public class Addition extends Opperation//Addition
{
    public int doAdd ()
    {
        return a+b;
    }
}//Addition

我知道有一種簡單的計算器制作方法，但是老師在7節課中要求使用它，而在新版本中，我仍然遇到相同的錯誤，指向點

Answer 1

您實例化Calculadora是錯誤的

res = new Calculadora.doAdd();  // wrong.

應該改為

res = new Calculadora().doAdd();  //correct

要么

Calculadora cal = new Calculadora();
res = cal.doAdd();