how can I retrieve instantiated objects of particular class in java?

Question

For instance,

// Object 1
SensorMeasurement tempSDSMInfo1 = new SensorMeasurement("temperatureMeasurement", tempSDStruct, "SensorDriver", "TemperatureSensor");

// Object 2
SensorMeasurement tempSDSMInfo2 = new SensorMeasurement("temperatureMeasurement", tempSDStruct, "SensorDriver", "TemperatureSensor");

//Object 3
SensorMeasurement tempSDSMInfo3 = new SensorMeasurement("temperatureMeasurement", tempSDStruct, "SensorDriver", "TemperatureSensor");

Now later in the program , I want to retrieve all the instantiated objects of a particular class ?

I do not want to store them in collection. Is there any other method?

It sounds like you want to form a collection of objects. Why do you not want to store them in a collection? — Oliver Charlesworth, Mar 03 '12 at 19:44

score 3 · Accepted Answer · answered Mar 03 '12 at 19:51

3

There is not really any other method. The best practice approach to this problem is to use a factory for SensorMeasurement, or a manager class. Then you will be able to reference them later through the factory or manager and have actions done in the factory or manager as well allowing for a centralized logic center.

answered Mar 03 '12 at 19:51

Travis J

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There is actually another method, via instrumentation, but I doubt it is what he is looking for. – Nikola Yovchev Mar 03 '12 at 21:03
@baba : can you explain instrumentation Method, if you can? – user-517752 Mar 03 '12 at 21:21
Well, basically, if you use an IDE, you have noticed that there is a possibility, when in debug mode, to see which classes have been loaded by the jvm, how many objects, etc. This is, of course, done on a snapshot at the current time. So if you find a way too hook into the debigging, you are set. Take a look at this: http://docs.oracle.com/javase/6/docs/api/java/lang/instrument/Instrumentation.html. As it states, instrumentation can give you information about the stats of the current jvm. I personally find that for the problem you described a factory would be sufficient (and less complex) – Nikola Yovchev Mar 03 '12 at 22:41

score 0 · Answer 2 · answered Mar 03 '12 at 19:55

You cannot do this directly in the Java language -- your only option is to store the desired object references in a collection.

For example, you could design your class as such:

public class SensorMeasurement {
  protected static Set<SensorMeasurement> allMeasurements = new HashSet();
  private SensorMeasurement(...) { }
  public static buildSensorMeasurement(String s, Object x, ...) {
    SensorMeasurement sm = new SensorMeasurement(s, x, ...);
    allMeasurements.add(sm);
    return sm;
  }
  public static Set<SensorMeasurement> getAllSensorMeasurements() {
    return new HashSet<SensorMeasurement>(allMeasurements);
  }
}

This way users of your class must use the "buildSensorMeasurement" factory method which will automatically add each instance to the collection which you can use as desired.

how can I retrieve instantiated objects of particular class in java?

2 Answers2