Question

我创建了一个程序，它将温度（double）和day（字符串）存储在arraylist中，然后使用类似的界面和插入排序对arraylist进行排序。现在我剩下的就是调用插入排序方法并打印出arraylist的原始顺序和排序顺序。但是，当我调用insertionsort方法时，它给出了一个错误，指出“无效的方法声明;需要返回类型”。为什么我收到此错误？也是我的打印声明正确打印出原始的arraylist？我如何更新它以打印排序的arraylist？或者我可以从insertionsort方法打印出来吗？

这是我的代码：

import java.io.*;
import java.util.Scanner;
import java.util.Arrays;
import java.util.ArrayList;


public class DailyTemperature implements Comparable<DailyTemperature>
{
     //variables
    private Double temperature;
    private String day;

    //getTemp & setTemp methods
    public double getTemp()
    {
      return temperature;
    }

    public void setTemp(double newTemp)
    {
      temperature = newTemp;
    }

    //getDay & setTEmp methods
    public String getDay()
    {
      return day;
    }

    public void setDay(String newDay)
    {
      day = newDay;
    }


    public DailyTemperature(String day, double temperature) 
    {
      this.day = day;
      this.temperature = temperature;
    }

    public int compareTo(DailyTemperature other) 
    {
        if (temperature < other.temperature) return -1;
        if (temperature == other.temperature) return 0;
        return 1;
    }

    public String toString() 
    {
        return("Day of Week" + this.getDay() +
        "Temperature" + this.getTemp());
    }


}



import java.io.*;
import java.util.Scanner;
import java.util.ArrayList;

public class DailyTemperatureList 
{
    public static void main (String [] args) 
    {

    ArrayList<DailyTemperature> dailytemps = new ArrayList<DailyTemperature>();

    dailytemps.add(new DailyTemperature("Mon", 87.1));
    dailytemps.add(new DailyTemperature("Tue", 88.3));
    dailytemps.add(new DailyTemperature("Wed", 81.2));
    dailytemps.add(new DailyTemperature("Thu", 84.0));
    dailytemps.add(new DailyTemperature("Fri", 76.3));
   }

   public static <DailyTemperature extends Comparable<? super DailyTemperature>>
   void insertionSort(ArrayList<DailyTemperature> dailytemps)
   {
       DailyTemperature temp = null;
       int position = 0;

       //loop from 2nd element on
       for (int i = 1; i < dailytemps.size(); i++)
       {
           temp = dailytemps.get(i);
           position = i;

           while ( 0 < position && temp.compareTo(dailytemps.get(position - 1 )) < 0)
           {
               dailytemps.set(position, dailytemps.get(position - 1));
               position--;
           }
            dailytemps.set(position,temp);
        }
    }

    insertionSort(ArrayList<DailyTemperature> dailytemps);
    System.out.println( dailytemps.toString() );





}

Answer 1

然而，当我调用insertionsort方法时，它给出了一个错误，指出“无效的方法声明;需要返回类型”。为什么我收到此错误？

您正在DailyTemperatureList类中调用insertionSort（），但在任何无法编译的方法之外。我将调用移动到main（）方法中，以便编译，请参阅下面的内容。

我的打印声明是否也正确打印出原始的arraylist？我如何更新它以打印排序的arraylist？或者我可以从insertionsort方法打印出来吗？

在调用insertionSort（）之前打印出原始列表，并在排序后打印出已排序的列表：

System.out.println( "original list:" );
System.out.println( dailytemps.toString() );

insertionSort( dailytemps);
System.out.println( "sorted list:" );

输出：

original list: [Day of WeekMonTemperature87.1, Day of WeekTueTemperature88.3, Day of WeekWedTemperature81.2, Day of WeekThuTemperature84.0, Day of WeekFriTemperature76.3] 

sorted list: [Day of WeekFriTemperature76.3, Day of WeekWedTemperature81.2, Day of WeekThuTemperature84.0, Day of WeekMonTemperature87.1, Day of WeekTueTemperature88.3]

更正了DailyTemperatureList类：

import java.io.*;
import java.util.Collections;
import java.util.Scanner;
import java.util.ArrayList;

public class DailyTemperatureList
{
  public static void main (String [] args)
  {

    ArrayList<DailyTemperature> dailytemps = new ArrayList<DailyTemperature>();

    dailytemps.add(new DailyTemperature("Mon", 87.1));
    dailytemps.add(new DailyTemperature("Tue", 88.3));
    dailytemps.add(new DailyTemperature("Wed", 81.2));
    dailytemps.add(new DailyTemperature("Thu", 84.0));
    dailytemps.add(new DailyTemperature("Fri", 76.3));

    System.out.println( "original list:" );
    System.out.println( dailytemps.toString() );

    insertionSort( dailytemps);
    System.out.println( "sorted list:" );
    System.out.println( dailytemps.toString() );



  }

  //public static <DailyTemperature extends Comparable<? super DailyTemperature>>
  static void insertionSort(ArrayList<DailyTemperature> dailytemps)
  {
    DailyTemperature temp = null;
    int position = 0;

    //loop from 2nd element on
    for (int i = 1; i < dailytemps.size(); i++)
    {
      temp = dailytemps.get(i);
      position = i;

      while ( 0 < position && temp.compareTo(dailytemps.get(position - 1 )) < 0)
      {
        dailytemps.set(position, dailytemps.get(position - 1));
        position--;
      }
      dailytemps.set(position,temp);
    }
  }






}

调用insertionsort方法时出错以及如何打印arraylist

1 个答案: