Question

I have following code :
I am trying to insert Item object in TreeSet and I am not getting desire output.

public class Main
{
    public static void main(String a[])
    {
        Item i1=new Item(1,"aa");
        Item i2=new Item(5,"bb");
        Item i3=new Item(10,"dd");
        Item i4=new Item(41,"xx");
        Item i5=new Item(3,"x5");
        TreeSet t=new TreeSet();    
        t.add(i1);
        t.add(i2);
        t.add(i3);
        t.add(i4);
        t.add(i5);
        System.out.println(t);      
    }
}
class Item implements Comparable<Item>
{
    String  nm;
    int price;
    public Item(int n,String nm)
    {
        this.nm=nm;
        price=n;
    }
    public int compareTo(Item i1)
    {
        if(price==i1.price)
            return 0;
        else if(price>=i1.price)
            return 1;
        else
            return 0;
    }
    public String  toString()
    {
        return "\nPrice "+price+" Name : "+nm;
    }    
}

Output :

[ Price 1 Name : aa,
Price 5 Name : bb,
Price 10 Name : dd,
Price 41 Name : xx ]

Item i5=new Item(3,"x5"); is not Inserted why?
Why I can do to insert in TreeSet.

Answer 1

You haven’t implemented compareTo() correctly. Here’s an extract from javadoc:

Compares this object with the specified object for order. Returns a negative integer,
zero, or a positive integer as this object is less than, equal to, or greater than
the specified object.

Your implementation doesn’t return -1 in case price of current object is less than price of object you compare with.