compare three variables and get the variable with min/max value back (not value)

Question

I have 3 variables with long values timestamp1 timestamp2 timestamp3 and an arraylist timestampList. I want to compare them in an if/else. It could be possible, that the three timestamps have different values, so I want to add the values with the min value to the list. I should also mention, that these timestamps are coming in every 2 minutes.

When the three variables are same, I could simply do

if(timestamp1 == timestamp2 && timestamp2 == timestamp3){
     timestampList.add(timestamp 1);   //since they are the same it doesn't matter which i add to the list
     .
     .
     .
}

now in the else or else if I want to check the three timestamps and get the variable with the min value, not the value itself. Because I need the variable for other variables further in the code. Of course I also want to add the min value to the list too. I can imagine, that I could do more if/else branches in the else like

else{
     if(timestamp1 < timestamp2){
          if(timestamp1 < timestamp3){
               ...
          }else{
               ...
          }
     }
}

but that would be too much and there is certainly a better way.

What is the type of your timestamps? Is it `int`, `long` or anything else? — Thomas Fritsch, Sep 04 '18 at 09:30
"get the **variable** with the min value, not the value itself" - Not really possible in Java. Instead, use a three-element array, and figure out the index of the smallest value; then you can use the combination of the array and the index as you would a variable reference. — Amadan, Sep 04 '18 at 09:30
Instead of `List` you should use `Set`, because `Set` automatically removes duplicates. — Thomas Fritsch, Sep 04 '18 at 09:34
Or use some sort of wrapper for the timestamps, e.g. an `Optional` or `AtomicLong`, then you can get the wrapper with the min/max value and update the value later on. — tobias_k, Sep 04 '18 at 09:38

score 0 · Answer 1 · answered Sep 04 '18 at 09:33

0

Try this:

    long timestamp1 = 1;
    long timestamp2 = 2;
    long timestamp3 = 3;
    long result = LongStream.of(timestamp1, timestamp2, timestamp3)
            .min()
            .getAsLong();

answered Sep 04 '18 at 09:33

talex

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score 0 · Answer 2 · answered Sep 04 '18 at 10:11

You can not really get a "pointer" to a variable in Java, as you could in C. The closest thing would be using a mutable type instead, so instead of assigning a new value to the variable you can modify an attribute of the existing instance, and the change will be reflected anywhere else in your code where you have a reference to that instance.

For example, you could wrap your long timestamps into AtomicLong instances:

// wrap in mutable AtomicLong instances
AtomicLong timestamp1 = new AtomicLong(123);
AtomicLong timestamp2 = new AtomicLong(456);
AtomicLong timestamp3 = new AtomicLong(789);

// get minimum or maximum, using streams or any other way
AtomicLong minTimeStamp = Stream.of(timestamp1, timestamp2, timestamp3)
        .min(Comparator.comparing(AtomicLong::get)).get();

// modify value
System.out.println(minTimeStamp); // 123
timestamp1.set(1000);             // change original variable
System.out.println(minTimeStamp); // 1000

score 0 · Answer 3 · answered Sep 04 '18 at 10:29

Another way to keep a variable to a certain value would be to use Optional<Long> as @tobias_k mentioned in his comment. An alternative to Stream would be to use a TreeSet. When creating the TreeSet we provide the Function to compare the elements. After all timestamps has been added, we can call TreeSet.first() to get the minimum element.

List<Optional<Long>> timestamps = Arrays.asList(Optional.of(1234l), Optional.of(2345l), Optional.of(1234l));
TreeSet<Optional<Long>> setOfTimestamps = new TreeSet<>(Comparator.comparing(Optional::get));
setOfTimestamps.addAll(timestamps);

Optional<Long> min = setOfTimestamps.first();
System.out.println(min.get());

score 0 · Accepted Answer · answered Sep 04 '18 at 11:49

So I went with the idea of @Amadan and created an array with the timestamps. But after thinking a little bit, I came to the conclusion that it would be possible without getting the variable.

long[] arrayDo = new long[3];
        arrayDo[0] = eafedo5.getServiceInformation(eafedo5Count).getTimestamp();
        arrayDo[1] = eafedo6.getServiceInformation(eafedo6Count).getTimestamp();
        arrayDo[2] = eafedo7.getServiceInformation(eafedo7Count).getTimestamp();

Then I calculate the minValue of the array.

long minTimestamp = Math.min(arrayDo[0],Math.min(arrayDo[1],arrayDo[2]));

Then I ask if the timestamps are equal to minValue

if(!timestamps.contains(minTimestamp)){
            timestamps.add(minTimestamp);
        }

        if(eafedo5.getServiceInformation(eafedo5Count).getTimestamp() ==minTimestamp){
            for(CHostNeighbor n : hostNeighborsEafedo5){
                msgsCountDo += n.getInboundMsgs();
            }
            eafedo5Count--;
        }
        if(eafedo6.getServiceInformation(eafedo6Count).getTimestamp() ==minTimestamp){
            for(CHostNeighbor n : hostNeighborsEafedo6){
                msgsCountDo += n.getInboundMsgs();
            }
            eafedo6Count--;
        }
        if(eafedo7.getServiceInformation(eafedo7Count).getTimestamp() ==minTimestamp){
            for(CHostNeighbor n : hostNeighborsEafedo7){
                msgsCountDo += n.getInboundMsgs();
            }
            eafedo7Count--;
        }

        msgsDo.add(msgsCountDo);

I mentioned in my question that I need the variable for later purposes. It was because I needed the name of the variable to decrement the count variable of the specific host. (the eafed... are hosts).

Thanks for all the answers!

compare three variables and get the variable with min/max value back (not value)

4 Answers4