CODEWITHSUNDEEP
java
Kaloyan Roussev
Kaloyan Roussev

Reputation: 14711

How to test is a passed object is a collection or an array

I have a logger class and here is one of its methods:

public static void i(String tag, Object message) {
    if (message != null) {
        i(tag, message.toString());
    } else {
        i(tag, ERROR_PARAMETER_IS_NULL_OR_EMPTY);
    }
}

this message!=null check is not sufficient for List, Map, Set or array, in the case when they are not null but they are empty. So how do I test if the passed object is something that has a size or a length so that I show the ERROR_PARAMETER_IS_NULL_OR_EMPTY message?

Upvotes: 1

Views: 106

Answers (3)

siom
siom

Reputation: 1807

You can use Class.isArray():

public static boolean isArray(Object obj)
{
    return obj!=null && obj.getClass().isArray();
}

Also works for arrays with primitive types.

And you can use Class.isAssignableFrom(Class<?> cls) to check whether object is an instance of Collection:

public static boolean hasSize(Object obj)
{
     return obj!=null && Collection.class.isAssignableFrom(obj.getClass());
}

Upvotes: 4

OldCurmudgeon
OldCurmudgeon

Reputation: 65803

You could avoid the test completely by overloading the method and providing an Iterable version.

// Shouldn't really use raw types here.
public static void i(String tag, Iterable messages) {
    if (messages != null) {
        /* 
        Probably need a bit more than this 
        as String.join takes an `Iterable<? extends CharSequence>
        but that is not an insurmountable problem.
        */
        i(tag, "["+String.join(",", messages)+"]");
    } else {
        i(tag, ERROR_PARAMETER_IS_NULL_OR_EMPTY);
    }
}

public static void i(String tag, Object message) {
    if (message != null) {
        i(tag, message.toString());
    } else {
        i(tag, ERROR_PARAMETER_IS_NULL_OR_EMPTY);
    }
}

Upvotes: 2

Olivier Gr&#233;goire
Olivier Gr&#233;goire

Reputation: 35417

To answer your broader question:

static boolean isEmptyArray(Object o) {
  if (o == null || !o.getClass().isArray()) {
    return false;
  }
  if (o instanceof int[]) {
    return ((int[])o).length == 0;
  } else if (o instanceof long[]) {
    return ((long[])o).length == 0;
  } else if (o instanceof double[]) {
    return ((double[])o).length == 0;
  } else if (o instanceof byte[]) {
    return ((byte[])o).length == 0;
  } else if (o instanceof char[]) {
    return ((char[])o).length == 0;
  } else if (o instanceof boolean[]) {
    return ((boolean[])o).length == 0;
  } else if (o instanceof float[]) {
    return ((float[])o).length == 0;
  } else if (o instanceof short[]) {
    return ((short[])o).length == 0;
  } else { // it is an array, so it can only be an object array now.
    return ((Object[])o).length == 0;
  }
}
static boolean isEmptyCollection(Object o) {
  return (o instanceof Collection) && ((Collection)o).isEmpty();
}

Upvotes: 1

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