java - 错误: cannot find symbol

Question

感谢您花时间看到这个，我已经尝试了到目前为止我所知道的一切，但在主程序(测试类)的第 7、10、13 和 16 行仍然遇到相同的错误

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

第二个程序:

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 ();
    }
}

具有操作属性的操作程序:

public class Opperation 
{
    public int a, b;

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

最后，操作还是比较简单的。

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

我知道有一种更简单的方法来制作计算器，但是老师在七个类(class)中要求它，我继续收到指向新中的点的相同错误

Answer 1

您实例化Calculadora的方式是错误的

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

应该改为

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

或

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