Generic Question

[kwgivler]

I'm trying to learn more about generics, but there are some problems in the DataSet class.
The problem seems to be here:

		if (maximum == null || x.compareTo(maximum) == 1)
			maximum = x;
		if (minimum == null || x.compareTo(minimum) == -1)
			minimum = x;

The simple classes are below. Any hints?

Thanks :)

package coin;

public class Tester {
	public static void main(String[] args)
	{
		DataSet<Coin> set = new DataSet<Coin>();
		set.add(new Coin(.10, "Dime"));
	}
}

package coin;

public class Coin implements Comparable<Coin>
{
	private double value;
	private String name;

	/**
      Constructs a coin.
      @param aValue the monetary value of the coin
      @param aName the name of the coin
	 */
	public Coin(double aValue, String aName) 
	{ 
		value = aValue; 
		name = aName;
	}

	/**
      Gets the coin value.
      @return the value
	 */
	public double getValue() 
	{
		return value;
	}

	/**
      Gets the coin name.
      @return the name
	 */
	public String getName() 
	{
		return name;
	}

	public int compareTo(Coin o) {
		if (this.value == o.value)
			return 0;
		if(this.value > o.value)
			return 1;
		else
			return -1;
	}
}

package coin;

public class DataSet<T>
{
	private Comparable<T> maximum;
	private Comparable<T> minimum;

	public DataSet()
	{
		minimum = null;
		maximum = null;
	}

	public void add(Comparable<T> x)
	{	
		if (maximum == null || x.compareTo(maximum) == 1)
			maximum = x;
		if (minimum == null || x.compareTo(minimum) == -1)
			minimum = x;
	}

	public Comparable<T> getMaximum()
	{
		return maximum;
	}
	
	public Comparable<T> getMinimum()
	{
		return minimum;
	}
}

[kwgivler]

Edit: sorry, I edited my original post. I'm still having problems with this :-\

[Junky]

Any chance you can tell us what those "problems" are or do we have to guess?

If you get error messages then copy and paste the EXACT messages and indicate which lines they occur on.

[kwgivler]

Sorry. I'm pretty sire the the problem is with the method

	public void add(Comparable<T> x)
	{	
		if (maximum == null || x.compareTo(maximum) == 1)
			maximum = x;
		if (minimum == null || x.compareTo(minimum) == -1)
			minimum = x;
	}

Eclipse shows the message:
The method compareTo(T) in the type Comparable<T> is not applicable for the arguments (Comparable<T>)

[kwgivler]

Exception in thread "main" java.lang.Error: Unresolved compilation problems:
The method compareTo(T) in the type Comparable<T> is not applicable for the arguments (Comparable<T>)
The method compareTo(T) in the type Comparable<T> is not applicable for the arguments (Comparable<T>)

at coin.DataSet.add(DataSet.java:16)
at coin.Tester.main(Tester.java:7)

[kwgivler]

If anyone is interested, here is the solution:

package coin;

public class DataSet<T extends Comparable<T>>
{
	private T minimum;
	private T maximum;


	public DataSet()
	{
		maximum = null;
		minimum = null;
	}

	public void add(T x)
	{	
		if (maximum == null || x.compareTo(maximum) == 1)
			maximum = x;
		if (minimum == null || x.compareTo(minimum) == -1)
			minimum = x;
	}

	public T getMinimum()
	{
		return minimum;
	}
	
	public T getMaximum()
	{
		return maximum;
	}
}