convert object to string getting can not cast error

Try the following:- use toString()

String output = relationshipInfo.toString();
output = output.replace("[", "");
output = output.replace("]", "");
System.out.println(output);

[UPDATE]

If you want fourth Object only then try:

    Object[] objArr = relationshipInfo.toArray();
    String groupedItemIds = String.valueOf(objArr[4]);

You cannot type cast Object to String unless the Object is indeed a String. Instead you can do the following -

Call toString() on it. Override it in your class.

you want "comma separated string" . So, you iterate over the 4th index and read each integer and do "" + int1 +" , " + int2 etc.. you can do this (in) by overriding your toString() method..

You could try:

String groupedItemIds = Arrays.asList( objArr[4] ).toString();

This will produce: groupedItemIds = "[1,2,3,4,5]"

Try this :

for(Object[] objArr : relationshipInfo)
{
      if(null != objArr[4])
       {
          String groupedItemIds = String.valueOf(objArr[4]);
       }
}  

Ref :

public static String valueOf(Object obj)

Returns the string representation of the Object argument.
Link.

Difference between use of toString() and String.valueOf()

if you invoke toString() with a null object or null value, you'll get a NullPointerExcepection whereas using String.valueOf() you don't have to check for null value.

It looks like you are using arrays not Lists in which case you can use:

String groupedItemIds = java.util.Arrays.toString(objArr[4]);

You cannot cast an Object to an uncomatible type

for(Object[] objArr : relationshipInfo){
if(null != objArr[4]){
List<Integer> groupedItemIds = (List<Integer)objArr[4];;

//Loop over the integer list
}

Integer Array or Integer can not be cast to a String.

try

for(Object[] objArr : relationshipInfo){
if(null != objArr[4]){
 String groupedItemIds =  new String (objArr[4]); // or String.valueOf(objArr[4]);
}

Update

If the 4th index is a Array then try

String groupedItemIds = Arrays.asList(objArr[4]).toString();

which will give you a comma delimitered String

I resolved my problem by belwo code

byte[] groupedItemIdsArr = (byte[])objArr[4];
String groupedItemIds = new String(groupedItemIdsArr);