公共类 Main 不起作用，这段代码甚至可能吗?

Question

我正在用Java做一些练习，我决定尝试一些东西，所以我让我的教授给我一些练习的想法，并提出了这个。当我在Eclipse中编译它时，它不起作用，它与公共类Main有关，但我不知道是什么。请告诉我我做错了什么，或者这是否有效。

这是我得到的错误

 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指出的，您还需要在单独的文件中声明类 main，或者将类 Forecast 设置为内部类。 我建议将预测类移到主类内 要做到这一点，你必须把它移到Main里面，就像你用函数一样。 (抱歉格式化我在手机上( 问题是你声明

String[] rainyDays;

然后你尝试吸收一个新值，如

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

但您已经将rainyDays定义为 String[]，因此您无法再次执行此操作
将其更改为

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

所以你的类看起来像这样：

 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

您有两个选择：

1-在其自己的文件中定义主类(与预测分开(

2-使主类成为嵌套类：你的代码将是这样的：

 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");
}
}