Java多文件和文件夹层次结构

我有多个Java文件，其中一个（Demo）是大多数函数所在的位置，DemoTest1是main所在的位置。 我尝试打包演示文件并在其他文件中使用该包，但是当我使用终端（javac…）编译时，DemoTest1没有编译，因为它还有一个函数，该函数包含一个参数，返回值是演示文件的一个对象

Demo.java文件：

package xyz.mypackage;

class  Demo{
    private  double val1;
    private  double val2;

    private void  setValues(double num1, double num2){
        val1 = num1;
        val2 = num2;
    }
    private double getValue1(){
        return (this.val1);
    }
    private double getValue2(){
        return (this.val2);
    }
    private double  getAverage(){
       return((this.val1 + this.val2) / 2);
    }

    public Demo(double double1, double double2){
        this.val1 = double1;
        this.val2 = double2;
    }

    static void decrDemo(Demo obj){
        obj.setValues(obj.val1 - 1, obj.val2 - 1);
    }
}

import java.util.Scanner; 
import xyz.mypackage.Demo;

public class DemoTest1{
    static Demo addDemo(Demo obj1, Demo obj2){
        return new Demo(obj1.getValue1() + obj2.getValue1(), obj1.getValue2() + obj2.getValue2());
    }

    static void incrDemo(Demo obj){
        obj.setValues(obj.getValue1() + 5, obj.getValue2() + 5);
    }

    public static void main(){
        Demo item = Demo();

        System.out.printl("\nPlease enter 2 numbers: ");
        Scanner input = new Scanner(System.in);
        double val1 = input.nextDouble();
        double val2 = input.nextDouble();
        demo.setValues(val1, val2);

        System.out.printl("\nThe average of the two values entered is: " + item.getAverage());

        Demo obj1 = new Demo(5, 7),
             obj2 = new Demo(14, 9);

        Demo objR = addDemo(obj1, obj2);

        incrDemo(obj1);

        System.out.printl("\nobjR has the following values. val1: &d\tval2: &d", objR.getValue1(), objR.getValue2());
        System.out.printl("\nobj1 has the following values. val1: &d\tval2: &d", obj1.getValue1(), obj1.getValue2());
    }
}

demost1.java文件：

package xyz.mypackage;

class  Demo{
    private  double val1;
    private  double val2;

    private void  setValues(double num1, double num2){
        val1 = num1;
        val2 = num2;
    }
    private double getValue1(){
        return (this.val1);
    }
    private double getValue2(){
        return (this.val2);
    }
    private double  getAverage(){
       return((this.val1 + this.val2) / 2);
    }

    public Demo(double double1, double double2){
        this.val1 = double1;
        this.val2 = double2;
    }

    static void decrDemo(Demo obj){
        obj.setValues(obj.val1 - 1, obj.val2 - 1);
    }
}

import java.util.Scanner; 
import xyz.mypackage.Demo;

public class DemoTest1{
    static Demo addDemo(Demo obj1, Demo obj2){
        return new Demo(obj1.getValue1() + obj2.getValue1(), obj1.getValue2() + obj2.getValue2());
    }

    static void incrDemo(Demo obj){
        obj.setValues(obj.getValue1() + 5, obj.getValue2() + 5);
    }

    public static void main(){
        Demo item = Demo();

        System.out.printl("\nPlease enter 2 numbers: ");
        Scanner input = new Scanner(System.in);
        double val1 = input.nextDouble();
        double val2 = input.nextDouble();
        demo.setValues(val1, val2);

        System.out.printl("\nThe average of the two values entered is: " + item.getAverage());

        Demo obj1 = new Demo(5, 7),
             obj2 = new Demo(14, 9);

        Demo objR = addDemo(obj1, obj2);

        incrDemo(obj1);

        System.out.printl("\nobjR has the following values. val1: &d\tval2: &d", objR.getValue1(), objR.getValue2());
        System.out.printl("\nobj1 has the following values. val1: &d\tval2: &d", obj1.getValue1(), obj1.getValue2());
    }
}

错误输出：

Air:Project xyz$ javac Demo.java DemoTest1.java
DemoTest1.java:2: xyz.mypackage.Demo is not public in xyz.mypackage;     
cannot be accessed from outside package
import xyz.mypackage.Demo;
                    ^
./Demo.java:3: duplicate class: xyz.mypackage.Demo
class  Demo
^
DemoTest1.java:6: cannot access Demo
bad class file: ./Demo.java
file does not contain class Demo
Please remove or make sure it appears in the correct subdirectory of    
the classpath.
static Demo addDemo(Demo obj1, Demo obj2)

如果我按照正确的说明操作，它应该会运行，但我想DemoTest1中并没有包含DemoDemo，我不理解这一点，因为我使用了打包。或者我是否需要编译不同于使用javac的文件。。然后用java运行DemoTest1

编辑：更改文件夹层次结构和修复语法错误使其成功编译，但在尝试运行它（java DemoTest1）时，我发现：

Exception in thread "main" java.lang.NoSuchMethodError: main  

Edit2:异常已修复。虽然main（）已经足够了，但它需要main（字符串args[]）。 现在它工作得很完美，正如它的初衷。我感谢您的帮助和学习机会

解决方案：适用于寻找类似问题的任何人。我在使用包时编写了xyz.mypackage，因此它必须位于这些文件夹/子文件夹中（我认为，它本身就是包的常规语法，不管文件夹如何），还必须添加默认构造函数，因为我添加了一个特殊构造函数，我错误地认为如果没有参数，它将只使用常规构造函数。

---

除了一些小的语法错误（没有正确使用println或使用%d而不是&f等）之外，另一个问题是main（）不能为空，它需要有一个参数（字符串args[]）。

您需要将Demo类声明为public。如果您可以检查错误，它确实明确提到了相同的错误

import java.util.Scanner; 

public class DemoTest1 {
    static Demo addDemo(Demo obj1, Demo obj2) {
        return new Demo(obj1.getValue1() + obj2.getValue1(), 
                obj1.getValue2() + obj2.getValue2());
    }

    static void incrDemo(Demo obj) {
        obj.setValues(obj.getValue1() + 5, obj.getValue2() + 5);
    }

    public static void main(String args[]) {
        Demo item = new Demo(0, 0);

        System.out.println("\nPlease enter 2 numbers: ");
        Scanner input = new Scanner(System.in);
        double val1 = input.nextDouble();
        double val2 = input.nextDouble();
        item.setValues(val1, val2);

        System.out.println("\nThe average of the two values entered is: " 
                + item.getAverage());

        Demo obj1 = new Demo(5, 7);
        Demo obj2 = new Demo(14, 9);

        Demo objR = addDemo(obj1, obj2);

        incrDemo(obj1);

        System.out.printf("\nobjR has the following values. val1: %.2f\tval2: %.2f", 
                objR.getValue1(), objR.getValue2());
        System.out.printf("\nobj1 has the following values. val1: %.2f\tval2: %.2f", 
                obj1.getValue1(), obj1.getValue2());
    }
}

---

演示类很好，但是这样试试应该可以。测试类中有一些语法错误。要调用double，可以使用

%.2f

表示小数点后两位的double，而不是原来的double。您也不需要将它们放入新的包或类似的东西中。

我认为这里可能有一些问题：

在Demost1中，您应该进行更改

import xyz.mypackage.Demo;

到

及

到

在演示中，您应该进行更改

class  Demo

到

并添加默认构造函数，因为您在DemoTest1文件中引用了一个构造函数

差不多

public Demo() {
    val1 = 0.0
    val2 = 0.0
}

---

是的，刚刚修好了。到达那里。出现语法错误，文件夹层次结构错误。现在它可以编译了，但当试图运行它时，我得到了一个新的错误..谢谢，我想&d对于一个小数来说已经足够了。我也不知道它需要包含main的参数。它现在工作得很漂亮，在研究的过程中我又学到了。

public class Demo

public Demo() {
    val1 = 0.0
    val2 = 0.0
}