Java类实例化错误解析：理解构造器与“实际与形式参数列表长度不同”问题

public class Calculator
{
    private double num1;
    private double num2;
    private double result;
    private char operator;

    // 自定义构造器，需要四个参数
    public Calculator (double a, double b, double r, char op)
    {
        this.num1 = a;
        this.num2 = b;
        this.result = r;
        this.operator = op;
    }
    // ... 其他方法（getter/setter, showcalculator, toString等） ...
}

public class CalculatorTest
{
    public static void main (String args[])
    {
        // 尝试调用无参数构造器
        Calculator C1 = new Calculator(); // 错误发生在此行
        // ...
    }
}

import java.util.Scanner;

public class CalculatorTest
{
    public static void main (String args[])
    {
        Scanner input = new Scanner (System.in);
        double a, b;
        char m;

        // 在创建对象时，直接传入构造器所需的参数
        // 这里的0.0和'+'是示例默认值，实际应用中可能需要根据业务逻辑确定
        Calculator C1 = new Calculator(0.0, 0.0, 0.0, '+'); // 传入默认参数以成功创建对象
        C1.showcalculator();

        System.out.println("Enter your first variable: ");
        a = input.nextDouble();
        System.out.println("Input your second variable: ");
        b = input.nextDouble();
        System.out.println("Input the operator: ");
        m = input.next().charAt(0);

        C1.setnum1(a);
        C1.setnum2(b);
        C1.setoperator(m);
        // ... 后续计算逻辑 ...
        input.close(); // 关闭Scanner
    }
}

public class Calculator
{
    private double num1;
    private double num2;
    private double result;
    private char operator;

    // 自定义带参数构造器
    public Calculator (double a, double b, double r, char op)
    {
        this.num1 = a;
        this.num2 = b;
        this.result = r;
        this.operator = op;
    }

    // 新增的无参数构造器
    public Calculator()
    {
        // 可以在这里设置成员变量的默认初始值，确保对象处于有效状态
        this.num1 = 0.0;
        this.num2 = 0.0;
        this.result = 0.0;
        this.operator = '+'; // 例如，设置一个默认操作符
    }

    // 以下是Calculator类的其他方法
    public void setnum1(double a) { this.num1 = a; }
    public double getnum1() { return num1; }
    public void setnum2(double b) { this.num2 = b; }
    public double getnum2() { return num2; }
    public void setoperator(char op) { this.operator = op; }
    public char getoperator() { return operator; }

    public void showcalculator()
    {
        System.out.println("Welcome!");
        System.out.println("1   2   3   +");
        System.out.println("4   5   6   -");
        System.out.println("7   8   9   *");
        System.out.println("0   00  .    /");
    }

    @Override
    public String toString()
    {
        return ("First variable:" + num1 + "\n Second variable:" + num2 + "\n Result of" + num1 + operator + num2 + "=" + result);
    }
}

import java.util.Scanner;

public class CalculatorTest
{
    public static void main (String args[])
    {
        Scanner input = new Scanner (System.in);
        double a,b;
        char m;

        // 现在可以成功调用无参数构造器
        Calculator C1 = new Calculator();
        C1.showcalculator();

        System.out.println("Enter your first variable: ");
        a = input.nextDouble();
        System.out.println("Input your second variable: ");
        b= input.nextDouble();
        System.out.println("Input the operator: ");
        m = input.next().charAt(0);

        C1.setnum1(a);
        C1.setnum2(b);
        C1.setoperator(m);
        // ... 后续计算逻辑 ...
        input.close(); // 关闭Scanner
    }
}