How to print an object which points to an array in Java

Question

I have a map which is defined like

HashMap<Object, Object> hashMap;

Now I need to iterate over each pair and print the key and value. Doing key.toString() and value.toString() works well for types like ArrayList. But toString() on an array won't give a readable string.

I am aware about Arrays.toString(). But I can't use it in my case because Arrays.toString() expects an object array and all I have is an object. So I wrote a custom code which looks like,

private String convertToHumanReadableFormat(Object value) {
    if (value == null) return "N/A";
    if (value.getClass().isArray()) {
        return convertArrayToReadableFormat(value);
    }
    return value.toString();
}

private String convertArrayToReadableFormat(Object value) {
    String output = "[";
    int arrayLength = Array.getLength(value);
    for (int i = 0; i < arrayLength; i++) {
        Object element = Array.get(value, i);
        if (element != null) {
            if (element.getClass().isArray()) {
                output += convertArrayToReadableFormat(element);
            }
            else {
                output += element.toString();
            }
        }
        if ((i + 1) < arrayLength)
            output += ", ";
    }
    output += "]";
    return output;
}

I am actually duplicating what Arrays.deepToString() does. But I can't see a way to just use Arrays.toString() or Arrays.deepToString().

Is this the correct approach to the problem or is there any way to get those standard methods working for me?

Any help would be great.

yes. I want to print the key and value as string. Key and value could be anything. Array's, lists etc. — Navaneeth K N
– Navaneeth K N, Commented Jun 22, 2012 at 7:02

Patton · Accepted Answer · 2012-06-25 05:13:09Z

1

Please modify the method convertToHumanReadableFormat to the following. I have tested it and it indeed worked.

private <T> String convertToHumanReadableFormat(Object value) {
            if (value == null) return "N/A";
            if (value.getClass().isArray()) {
                if( value instanceof int[]||value instanceof long[]){
                    List<T> list = new ArrayList<T>();
                    list.addAll((Collection<? extends T>) Arrays.asList(value));
                    return convertToHumanReadableFormat(list.toArray());

                }else{
                     return Arrays.deepToString((Object[]) value);
                }
            }
            return value.toString();
        }

You can add other primitive types to the if condition.

edited Jun 25, 2012 at 5:13

answered Jun 22, 2012 at 6:54

Patton

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1 Comment

Navaneeth K N Over a year ago

This won't work when value = new int[] {10} because you can't cast int[] to Object[].

Yair Zaslavsky · Accepted Answer · 2012-06-22 06:53:16Z

0

There are several approaches you can consider -
A. If you're not to strict on the format, and just want to print the HashMap contents in a human readable way, I would suggest you to use JSon serializing - the output if quite human readable.
You can see what we did at Ovirt open source project (clone the git repo of the engine project) - engine\backend\manager\modules\utils\src\main\java\org\ovirt\engine\core\utils\serialization\json - look at the JsonObjectSerializer class there.

B. If you are strict on the format - You should get the entrySet of your map, iterate over it, and insert the objects into an ArrayList . After that you can use the toArray() method to return an array, and use the method you described above.
Bare in mind that I suggest that your ArrayList will be an ArrayList of Strings, so you must take each mapEntry and translate it string, consider the toString() and see if the format it produces is good enough for you.

answered Jun 22, 2012 at 6:53

Yair Zaslavsky

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1 Comment

Navaneeth K N Over a year ago

Thank you for the suggestion. But the code that I have posted here works in all the cases. It works for Arrays, multi dimensional arrays, lists, maps etc. All I was wondering is any alternate way to do this using standard library methods.

Konstantin Pribluda · Accepted Answer · 2012-06-22 06:53:31Z

0

If you use case is rendering arrays and other object graphs in human readable form you may go for templating solution (like velocity of freemarker) or convert them to JSON (or XML) and rpetty pring it - I would recommend GSON / XStream for this task.

If you like to have it for debug purposes, then just stick with logging system and use standart converters available there ( for example in log4j)

answered Jun 22, 2012 at 6:53

Konstantin Pribluda

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Comments

Kshitij · Accepted Answer · 2012-06-22 07:12:35Z

0

what if you convert array to list and then use toString -

Arrays.asList(array)

you will need to write your helper method this way -

private String convertToHumanReadableFormat(Object value) {
    if (value == null) return "N/A";
    if (value.getClass().isArray()) {
       value = Arrays.asList((Object[])value);     
    }     
    return value.toString(); 
}

to handle primitives you will need to first manually convert array to list -

private String convertToHumanReadableFormat(Object value) {
    if (value == null) return "N/A";
    if (value.getClass().isArray()) {

       //convert array to list 
       int count = Array.getLength(value);
       ArrayList<Object> list = new ArrayList<Object>();
       for(int i=0; i<count; i++){
          list.add(Array.get(value, i));
       } 
       return list.toString(); //or value=list;  
    }     
    return value.toString(); 
}

edited Jun 22, 2012 at 7:12

answered Jun 22, 2012 at 6:42

Kshitij

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6 Comments

Navaneeth K N Over a year ago

Not really. Arrays.asList() wraps the array in a list. List will have only one element and first element points to this array. Not helpful.

Kshitij Over a year ago

i guess you missed the part to cast the value object to Object[] first

Navaneeth K N Over a year ago

This also won't work. Will break when value = new int[] {10}. Casting from int[] to Object[] is invalid.

Kshitij Over a year ago

not really... It does not just creates a new List and add array into it. When you do Arrays.asList your entire array gets converted into equivalent List object of same length.

Kshitij Over a year ago

good point...will need some special handling to handle primitives

|

Daniel · Accepted Answer · 2012-06-22 08:39:08Z

0

You could just use nine instanceof statements to call the appropriate toString or deepToString method. If you do use your own code, remember to use a StringBuilder and to take into account the possibility of an array containing a reference to itself or a parent dimension. Currently your code would recurse until stack overflow. Using instanceof as I suggest would also avoid the boxing of primitive values that is inherent in your code (and thus improve performance). Nine statements isn't too many, is it?

if (val instanceof Object[]) return Arrays.deepToString((Object[]) val);
if (val instanceof byte[]) return Arrays.toString((byte[]) val);
// Repeat for other 7 array types...

edited Jun 22, 2012 at 8:39

answered Jun 22, 2012 at 8:27

Daniel

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