implementing compareTo method for several fields

Question

I want to compare two object based on 5-tuple which are: srcAddr, dstAddr, srcPort, dstPort, protocol

here is what i have:

public class Flows implements          


        

Answer 1

The compiler / code checker is warning you that comparing String values with == is almost always a mistake.

But fixing that won't really help because your code does nothing like what a correctly implemented compareTo method should do.

A straight-forward implementation of compareTo for your Flows class would be:

public int compareTo(Flows other) {
    int res = this.srcAddr.compareTo(other.srcAddr);
    if (res != 0) {
        return res;
    }
    res = this.dstAddr.compareTo(other.dstAddr);
    if (res != 0) {
        return res;
    }
    res = this.srcPort.compareTo(other.srcPort);
    if (res != 0) {
        return res;
    }
    res = this.dstPort.compareTo(other.dstPort);
    if (res != 0) {
        return res;
    }
    return this.protocol.compareTo(other.protocol);
}

That assumes the the fields are never null. If they are, then write a safeCompare(String, String) method that takes care with nulls and apply it to each field as above.

EDIT

Given that you are defining compareTo you also ought to declare equals and hashCode to be consistent with them. Otherwise certain collection methods are likely to behave incorrectly.

EDIT 2

The compiler error you mention in a comment on how to override compareTo method happens because the int compareTo(Flow flow) method actually implements the compareTo method of Comparable. If you are going to declare Flow as implementing the raw interface type Comparable then the signature needs to be

public int compareTo(Object obj) {
    Flow flow = (Flow) obj;
    ...

But a better solution would be to change the class declaration to:

public class Flows implements Serializable, Comparable {
...