Thread: Arrays.Sort Help

I have an array called list that contains string id, and double temp //names and values for weather stations

I want to sort the list by the value temperature.


public void Display2()
{
Arrays.sort(List);-

HOW DO I SORT BY TEMP?? GetID is the getter method for string id, and GetTemp is the getter method for GetTemp. Temp and ID were initialized on another .java file --WeahterStationData.java if that helps

System.out.println("Highest Temperature: " + List[0].GetID() + List[0].GetTemp());
System.out.println("Lowest Temperature: " + List[CurrSize].GetID() + List[CurrSize].GetTemp());

}

Exception in thread "main" java.lang.ClassCastException: WeatherStationData cannot be cast to java.lang.Comparable
at java.util.Arrays.mergeSort(Unknown Source)
at java.util.Arrays.mergeSort(Unknown Source)
at java.util.Arrays.mergeSort(Unknown Source)
at java.util.Arrays.sort(Unknown Source)
at WeatherStationList.Display2(WeatherStationList.jav a:58)
at WeatherStationUI.RunIT(WeatherStationUI.java:36)
at WeatherStationUI.<init>(WeatherStationUI.java:18)
at Main.main(Main.java:11)

Sorry.

/*
 * title: Main.java
 * name: Brandon Seale
 * date: 2/16
 * comments: used Happy Inventory as framework for project. 
 */
public class Main { 
 
	public static void main(String[] args)
	{
		WeatherStationUI NewList = new WeatherStationUI();
	}
 
}

/*
 * Title:			WeatherStationData.java
 * Description:		This represent a single Weather Station
 * 
 */
 
public class WeatherStationData {
	private String StationID;  //Each Station must have a unique identifier...
	private double StationTemp;
 
 
 
	public WeatherStationData() //Define a default constructor...
	{
		StationID = "";		
		StationTemp = 0.0;
 
	}
 
	public WeatherStationData(String ID, double Temp) //...intializer
	{
		StationID = ID;
		StationTemp = Temp;
 
 
 
	}
 
	//Define some setter methods...
 
	public void SetID(String ID)  { StationID = ID; }
	public void SetTemp(double Temp) { StationTemp = Temp; }
 
 
	//Define some getter methods...
 
	public String GetID()  { return StationID; }
	public double GetTemp()  { return StationTemp; }
 
 
}

/*
 * Title:			WeatherStationUI.java
 * Description:		Supplies a frame for using the WeatherStationList class...
 */
 
 
import java.util.*;
 
 
public class WeatherStationUI {
 
	WeatherStationList Collection = new WeatherStationList(); // to store data
	Scanner Input = new Scanner(System.in); // new scanner
 
 
 
 
	public WeatherStationUI() { RunIT(); } 
 
	public void RunIT()
	{
 
	   String Command;
 
	   while(true) {
		   Menu(); // menu
 
		   System.out.print("Command: "); //uses next line as command
		   Command = Input.nextLine();
 
		if(Command.equals("Quit")) // "Quit" breaks from program
			   break;
		   else if(Command.equals("Post Temperatures"))	 
			   PostTemperatures();	
[B]	   
		   else if(Command.equals("High-Low Report")) // to view high low			   
			   	Collection.Display2();[/B]
		   else if(Command.equals("Daily Report")) // view all
			   Collection.Display();
 
	   }
 
 
	}
 
 
 
	public void Menu() //choices
	{
		System.out.println("Choices.......................................");
		System.out.println("\tPost Temperatures...allows the user to post new stations");
		System.out.println("\tHigh-Low Report...allow the user to view high to low.");
		System.out.println("\tDaily Report.....displays the entire list.");
		System.out.println("\tQuit");
		System.out.println("----------------------------------------------");
	}
 
	public void PostTemperatures() //posts temps
	{
		String ID, Unit;
		double Temp;
 
		while(true){
 
 
				System.out.print("Station Name: "); //prompts for station name
				ID = Input.nextLine(); // puts next line as id
 
				if(ID.equals("Stop")) //breaks
					break;
 
				System.out.print("Station Temp: ");
				Unit = Input.nextLine(); 
				Temp = Double.parseDouble(Unit); //turns into double
				Collection.Add(ID, Temp); 
 
 
 
 
 
 
 
		}
 
 
	}
 
 
 
 
 
 
 
}

/*
 * Title:		WeatherStationList.java
 * Description: this implements and manages a list of inventory items...
 */
import java.text.DecimalFormat;//in order to display in decimal format
import java.text.NumberFormat;//same
import java.util.*;
 
 
public class WeatherStationList {
 
	private int MaxSize = 25;  //The value here is the List's absolute size...
	private int CurrSize = 0;  //The number of item currently list...
 
	public WeatherStationData[] List = new WeatherStationData[MaxSize];
 
 
 
	//Define the core methods for the list...
 
	//First a way to add items to the list...
 
	public void Add(String ID, double Temp)
	{
		if(CurrSize < MaxSize) {  //Make sure there's room...
			List[CurrSize] = new WeatherStationData(ID, Temp); //Then add it...
			CurrSize++; //Bump the count up, because there's one more...
		}
		else
			System.out.println("Sorry List Is Full"); //Whoops! no more room...
	}
 
 
 
 
 
	public void Display()
	{
		int K;
 
		for(K = 0 ; K < CurrSize ; K++)  {
			if(List[K] != null) {
				NumberFormat Rounder = new DecimalFormat("#0.00"); //displays in 0.00 decimal format
 
				System.out.println("Weather Station:   " + List[K].GetID()); //gets station id
				System.out.println("Temperature: " + List[K].GetTemp() + "    " + Rounder.format(((5*(List[K].GetTemp()-32))/9)));//shows temp in F and Celcius
 
			}
		}
 
 
 
	}
 
 
	[B]public void Display2()
	{
 
                        [QUOTE]What Code Do i enter here to sort the list by the value of the Double Temp?
			 Arrays.sort(List);
[/QUOTE]
 
			System.out.println("Highest Temperature: " + List[0].GetID() + List[0].GetTemp());
			System.out.println("Lowest Temperature: " + List[CurrSize].GetID() + List[CurrSize].GetTemp());
 
	}[/B]
 
 
 
 
 
 
 
 
}

Arrays (Java Platform SE 6)

Also, that

while(true)
thing will almost certainly be an infinite loop. (Unless you have a break somewhere else.)

Also, you should probably have your Menu() method be changed to this:

 
public void Menu(String Command)
{
System.out.println("Choices.......................................");
		System.out.println("\tPost Temperatures...allows the user to post new stations");
		System.out.println("\tHigh-Low Report...allow the user to view high to low.");
		System.out.println("\tDaily Report.....displays the entire list.");
		System.out.println("\tQuit");
		System.out.println("----------------------------------------------");
 
 
if(Command.equalsIgnoreCase("Quit")) // "Quit" breaks from program
			   break;
		   else if(Command.equalsIgnoreCase("Post Temperatures"))	 
			   PostTemperatures();	
 
		   else if(Command.equalsIgnoreCase("High-Low Report")) // to view high low			   
			   	Collection.Display2();
		   else if(Command.equalsIgnoreCase("Daily Report")) // view all
			   Collection.Display();
 
else
{
// what happens if they enter an invalid command?
}
}
 
// Also, why are you entering commands instead of say having options associated with each choice and passing it an int as // a parameter and not even bothering with String?  It'd be more convenient for the user of your program if you did it 
// this way.

As it is, I have changed it to equalsIgnoreCase(String str) in case they don't start with a capital. Java is very annoyingly picky and will say it's not equal if you do something as trivial as forgetting a space so that it doesn't match up with the thing you have in the equals parameter.

Very annoying, I know



the constructor that takes as a parameter the result of a void method is not a good idea.

If anything, you'd have a no param constructor and do something like this:

public WeatherStationUI()
{
RunIt();
}

Third, a Scanner only works that I'm aware of in the main method or at least in a class that has a main method.

Thanks everyone, for help, just finished program. Didn't need to incorporate comparables/compare to for what i'm doing

-Brandon Seale