dr.java中的空指针异常

我试图制作一个程序，在那里我可以输入一定的天数和起始温度。温度在一天中以某种方式变化。然后打印最后一天的温度。我的教授说使用类TempPattern、字段num_days和first_day_temp以及构造函数和finalTemp方法。以下是我所拥有的：

  public class TempPattern{ 

    int num_of_days = 0;
    int temp_first_day = 0;

    public void TempPattern(int temp, int days){
         days = num_of_days;
         temp = temp_first_day; 
    }
      public int num_of_days(int days){
       return days;
      }
      public int temp_first_day(int temp){
        return temp;
      }

      }

        public void finalDayTemp(int days, int temp){
           int half = days / 2; 
           int newtemp = temp + 2;                                                     

              for (int current_day = 1; current_day <= half; current_day++){        
                  newtemp = newtemp - 2;                                                
             }
              for (int current_day = half + 1; current_day <= days; current_day++){ 
                  newtemp++;                                                        
             }
              System.out.println("Temperature on final day would be " + newtemp);
      }
         public void main(String[] args){
         Scanner keyboard = new Scanner(System.in);           
           int days;                                         
           int temp; 

          System.out.print("number of days: ");   
             days = keyboard.nextInt();                                        

          System.out.print("temperature of first day: ");              
             temp = keyboard.nextInt(); 

             finalDayTemp(days,temp);
       }

---

我认为有些东西是空值，但我真的不知道如何修复它。我也认为我没有正确地完成整个构造函数和字段的工作，所以请随时提供任何帮助/建议，我非常感谢。我会清理一切不合理的东西。提前完成。

这里有两件事需要改变：

• 主方法应该而且必须是静态的
• findFindFinalDay（）方法应该是静态的，以便从main（）方法调用它
• TemperaturePattern类不应该是公共的，因为它的目的是作为内部类（根据我的理解）

查找以下修改的代码：

import java.util.Scanner;
public class HWfive{ 
        public static void findFinalDayTemperature(int days, int temp){
           int half = days / 2; 
           int newtemp = temp + 2;
          for (int current_day = 1; current_day <= half; current_day++){        
                  newtemp = newtemp - 2;                                                
             }
          for (int current_day = half + 1; current_day <= days; current_day++){ 
                  newtemp++;                                                        
             }
              System.out.println("Temperature on final day would be " + newtemp);
      }
         public static void main(String[] args){
         Scanner keyboard = new Scanner(System.in);           
           int days;                                         
           int temp;
          System.out.print("number of days: ");   
             days = keyboard.nextInt();                                      
          System.out.print("temperature of first day: ");              
             temp = keyboard.nextInt(); 
             findFinalDayTemperature(days,temp);
       }
class TemperaturePattern{ 
    int num_of_days = 0;
    int temp_first_day = 0;
     public void TemperaturePattern(int temp, int days){
         days = num_of_days;
         temp = temp_first_day; 
        }    
     public int num_of_days(int days){
       return days;
      }    
     public int temp_first_day(int temp){
        return temp;
      }
      }
}

import java.util.Scanner；
公共类HW5{
公共静态无效FindFindFindayTemperature（整数天，整数温度）{
int半=天/2；
int newtemp=温度+2；
对于（int current_day=1；current_day main method应该是静态的。非常感谢您的帮助~您介意解释为什么这些方法必须是静态的吗？@JNV我很高兴它起到了作用。请查找我对静态修饰符的更新。@JNV另外，如果它有帮助，请投票决定答案。
import java.util.Scanner;
public class HWfive{ 
        public static void findFinalDayTemperature(int days, int temp){
           int half = days / 2; 
           int newtemp = temp + 2;
          for (int current_day = 1; current_day <= half; current_day++){        
                  newtemp = newtemp - 2;                                                
             }
          for (int current_day = half + 1; current_day <= days; current_day++){ 
                  newtemp++;                                                        
             }
              System.out.println("Temperature on final day would be " + newtemp);
      }
         public static void main(String[] args){
         Scanner keyboard = new Scanner(System.in);           
           int days;                                         
           int temp;
          System.out.print("number of days: ");   
             days = keyboard.nextInt();                                      
          System.out.print("temperature of first day: ");              
             temp = keyboard.nextInt(); 
             findFinalDayTemperature(days,temp);
       }
class TemperaturePattern{ 
    int num_of_days = 0;
    int temp_first_day = 0;
     public void TemperaturePattern(int temp, int days){
         days = num_of_days;
         temp = temp_first_day; 
        }    
     public int num_of_days(int days){
       return days;
      }    
     public int temp_first_day(int temp){
        return temp;
      }
      }
}