Public class Main 不工作，这段代码是否可行？

Question

我正在用 Java 做一些练习，我决定尝试一些东西，所以我请我的教授给我一些练习的想法，然后想出了这个。当我在 Eclipse 中编译它时，它不起作用，它与 public class Main 有关，但我不知道是什么。请告诉我我做错了什么，或者这是否可行。

This is the error I get

 public class Forecast 
{
    public int temperature;
    public int pressure;

}

public class Main
{
    public static void changeTheString(String weather)
    {
        weather = "sunny";
    }

    public static void changeTheArray(String[] rainyDays)
    {
        rainyDays[1] = "Sunday";
    }
    public static void changeTheObject(Forecast forecast)
    {
        forecast.temperature = 35;
    }
    public static void main (String[] args)
    {
        String weather = "rainy";
        changeTheString(weather);
        String[] rainyDays;
        System.out.println("The rainy days were on " + rainyDays[0] + " and " + rainyDays[1]);

        String[] rainyDays = new String[] {"Monday", "Friday"};
        changeTheArray(rainyDays);
        System.out.println("The rainy days were on " + rainyDays[0] + " and " + rainyDays[1]);

        Forecast forecast = new Forecast();
        forecast.pressure = 700;
        forecast.temperature = 20;
        changeTheObject(forecast);
        System.out.println("The temperature is " + forecast.temperature + " Celsius");

    }

}

Answer 1

正如 aziz_aon 所指出的，您还需要在单独的文件中声明 class main 或将 class Forecast 设为内部 class。我建议将 Forecast class 移动到 Main class 内为此，您必须将它移动到 Main 中，就像使用函数一样。（抱歉格式化我在手机上）问题是你声明

String[] rainyDays;

然后您尝试指定一个新值，例如

String[] rainyDays = new String[] {"Monday", "Friday"};

但是您已经将 rainyDays 定义为 String[]，所以您不能再这样做了
将其更改为

rainyDays = new String[] {"Monday", "Friday"};

所以你的 class 看起来像这样：

 public class Forecast 
 {
     public int temperature;
     public int pressure;

}

public class Main
{
    public static void changeTheString(String weather)
    {
        weather = "sunny";
    }

    public static void changeTheArray(String[] rainyDays)
    {
    rainyDays[1] = "Sunday";
    }
    public static void changeTheObject(Forecast forecast)
    {
        forecast.temperature = 35;
    }
    public static void main (String[] args)
    {
    String weather = "rainy";
    changeTheString(weather);
    String[] rainyDays;
    System.out.println("The rainy days were on " + rainyDays[0] + " and " + rainyDays[1]);

    rainyDays = new String[] {"Monday", "Friday"};
    changeTheArray(rainyDays);
    System.out.println("The rainy days were on " + rainyDays[0] + " and " + rainyDays[1]);

    Forecast forecast = new Forecast();
    forecast.pressure = 700;
    forecast.temperature = 20;
    changeTheObject(forecast);
    System.out.println("The temperature is " + forecast.temperature + " Celsius");

}

}

Answer 2

你有两个选择：

1- 在其自己的文件中定义主要 class（与 Forecast 分开）

2- 将主 class 设为嵌套 class：您的代码将如下所示：

 public class Forecast 
{
public int temperature;
public int pressure;

public class Main
{
    public static void changeTheString(String weather)
    {
        weather = "sunny";
    }

    public static void changeTheArray(String[] rainyDays)
    {
        rainyDays[1] = "Sunday";
    }
    public static void changeTheObject(Forecast forecast)
    {
        forecast.temperature = 35;
    }
}


public static void main (String[] args)
{
    String weather = "rainy";
    changeTheString(weather);
    String[] rainyDays;
    System.out.println("The rainy days were on " + rainyDays[0] + " and " + rainyDays[1]);

    String[] rainyDays = new String[] {"Monday", "Friday"};
    changeTheArray(rainyDays);
    System.out.println("The rainy days were on " + rainyDays[0] + " and " + rainyDays[1]);

    Forecast forecast = new Forecast();
    forecast.pressure = 700;
    forecast.temperature = 20;
    changeTheObject(forecast);
    System.out.println("The temperature is " + forecast.temperature + " Celsius");

}

}

Public class Main 不工作，这段代码是否可行？

Public class Main not working, is this code even possible or?

java

main