Question

What I do not understand is why I am getting an error compiling my code when a String is in fact an object, and the compiler is saying otherwise. I dont know why I keep getting this error message

  symbol:   method compareTo(Object)
  location: variable least of type Object
.\DataSet.java:17: error: cannot find symbol
   else if(maximum.compareTo(x) < 0)

here is the code. I’m trying to utilize the class comparable to allow two objects to use the compareTo method. In the tester, I’m just trying to use a basic string object to compare.

public class DataSetTester
{
public static void main(String[] args)
{
    DataSet ds = new DataSet();
    String man = "dog";
    String woman = "cat";
    ds.add(man);
    ds.add(woman);
    System.out.println("Maximum Word: " + ds.getMaximum());


 }
}

Class:

public class DataSet implements Comparable 
{
 private Object maximum;
 private Object least;
 private int count;
 private int answer;

 public void add(Object x)
 {

   if(count == 0){
     least = x;
     maximum = x;
   }
   else if(least.compareTo(x) > 0)
     least = x;
   else if(maximum.compareTo(x) < 0)
    maximum = x;
   count++;
 }

 public int compareTo(Object anObject)
 {
     return this.compareTo(anObject);
 }

 public Object getMaximum()
 {
  return maximum;
 }

 public Object getLeast()
 {
   return least;
 }
}

Comparable Interface:

public interface Comparable
{
    public int compareTo(Object anObject);
}

Answer 1

The problem is that DataSet implements Comparable, but Object doesn’t.

Instead of storing Objects, you want to store Comparables. However, if you do get this to compile, you will get into an infinite loop right here:

public int compareTo(Object anObject) 
{
    // Yeah, never stop loopin'!
    return this.compareTo(anObject);
}

It’s recommended that in newer code, you use the generic Comparable<T> interface. Your code would then look like this:

public class DataSet implements Comparable<DataSet>  
{  
 private String maximum;  
 private String least;  
 private int count;  
 private int answer;  

 public void add(String x)  
 {  

   if(count == 0){  
     least = x;  
     maximum = x;  
   }  
   else if(least.compareTo(x) > 0)  
     least = x;  
   else if(maximum.compareTo(x) < 0)  
    maximum = x;  
   count++;  
 }  

 public int compareTo(DataSet anObject)  
 {  
     // I don't really know how you want this to work.
     // Come up with your own criteria on what makes a DataSet greater or less than
     // another one.
     count - anObject.count
 }  

 // Good practice to include this if you're doing a compareTo.
 @Override
 public boolean equals(Object other)
 {
     return (other instanceof DataSet) && compareTo((DataSet)other) == 0;
 }

 public String getMaximum()  
 {  
  return maximum;  
 }  

 public String getLeast()  
 {  
   return least;  
 }  
}  

Edit – just saw that you’re comparing strings. In that case, you don’t really need DataSet to implement Comparable. However, if you do need it for something else, what I wrote still stands.