TreeSet Update Object Value seems to be a Bug in Implementation

Question

I was checking tree set and notice that I am unable to update the value in Tree set for my user defined Object

e.g

class Emp implements Comparable<Emp>
{
int id;
String name;

public Emp(int id,String name)
{
    this.id=id;
    this.name=name;
}

@Override
public int compareTo(Emp obj) {
        if(obj.id>this.id)
            return -1;
        else if(obj.id<this.id)
            return 1;
        else
            return 0;
}

@Override
public String toString() {
    return "Emp Id:"+id+" Emp Name:"+name;
}
}
public static void main(String[] args) {
    treesetwithCustom();
}

public static void treesetwithCustom()
{
    TreeSet<Emp> set=new TreeSet<Emp>();
    set.add(new Emp(1,"ABC"));
    set.add(new Emp(2,"XYZ"));
    set.add(new Emp(1,"PQR"));
    System.out.println(set);
}

When I print the set it shows the value for Emp ID 1 as ABC and not PQR

when I check in rt.jar for tree set implementation I notice there seems to be a bug in Implementation as TreeSet Internally uses implementation provided by TreeMap and call put method of TreeMap.

In rt.jar the put code Update the value and not Key and in TreeSet the value for Key is always passed as present

Please help me understand if is there any way to achieve the update in tree set and if my understanding is correct about the bug.

_Adds the specified element to this set if it is not already present._ What do you make of that? — Sotirios Delimanolis, Nov 29 '15 at 00:54
when I put the emp object with same ID with different name hash set keep the old object even if the value for Name is changes how can I update the value in TreeSet — Sandesh Dhotre, Nov 29 '15 at 01:01
That's the expected behavior of `TreeSet` as the quote from the javadoc from my last comment states. — Sotirios Delimanolis, Nov 29 '15 at 01:03
if you want to change an element in the set, you need to first remove, then add. — jtahlborn, Nov 29 '15 at 01:04
Yup. This is working as Java intended, even if it's not what you expected. — Louis Wasserman, Nov 29 '15 at 02:23

score 0 · Answer 1 · edited May 23 '17 at 11:52

As others have already explained, the described behaviour is to be expected and explicitly specified in the JDK API description for class TreeSet.

If you are looking for a way to keep your collection up to date, check out my UpdateableTreeSet implementation. There are a few articles here on SO which relate to the same problem and also to UpdateableTreeSet:

TreeSet Update Object Value seems to be a Bug in Implementation

1 Answers1