Uninitialized object vs new object

Question

How are these code snippets different from each other:

Snippet 1: HashMap map1= abc() ;

Snippet 2: HashMap map2= new HashMap();
           map2 = abc();

I'm getting OutOfMemoryError in my application. Can the reason of this error due to the implementation of Snippet 1 in my code?

Edit: Added implementation of abc()

public HashMap abc(){
    HashMap  rMap = null;

    StringBuffer  sQuery = new StringBuffer("");

     sQuery.append(" SELECT DISTINCT ABC ,DEF, ");
     sQuery.append(" XYZ, ID, NAME  ");
     sQuery.append(" FROM TABLE1");

    Query query = new Query( sQuery.toString());

    List rList = query.executeSelect();

    if (rList != null && rList.size() > 0) {
        Iterator listIter = rList.iterator();
        Map map = null;
         rMap = new HashMap();
        while (listIter.hasNext()) {
            map = (HashMap) listIter.next();

            String key = map.get("ABC") + "%"+ map.get("DEF")+"%"+map.get("XYZ");
            if( rMap.containsKey(key)){
                LinkedHashMap sMap = (LinkedHashMap) rMap.get(key);
                sMap.put(map.get("ID"), map.get("NAME"));
                 rMap.put(key, sMap);

            }else{
                LinkedHashMap sMap = new LinkedHashMap();
                sMap.put(map.get("ID"), map.get("NAME"));
                 rMap.put(key, sMap);
            }
        }
    }
    return  rMap;
}

Snippet 2 creates additional HashMap instance that is never used (which means Snippet 1 is better), but without seeing the code of `abc()` it's hard to tell what's causing your OutOfMemoryError. — Eran, Aug 04 '15 at 10:42
At the time `map2 = abc()` is exectuted, first `HashMap`in snippet 2 is elegible for garbage collection, so that's not the problem. — Fran Montero, Aug 04 '15 at 10:44
@KLCoder That's not enough information. How often are you calling abc? Does each call to abc produce a new HashMap, or does it return the same instance in each call? Can you show the code of abc? — Eran, Aug 04 '15 at 10:51

score 1 · Answer 1 · answered Aug 04 '15 at 10:54

1

In Snippet 2 you create an extra instance which would be eligible for garbage collection on the next statement. So basically they're the same and it shouldn't cause a memory leak.

Try running a profiler to check memory map or increase the heap size.

answered Aug 04 '15 at 10:54

dogant

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score 0 · Answer 2 · edited May 23 '17 at 11:43

Your problem seems to be in another part of your code. Try setting an automatic heapdump when a OutOfMemoryError occurs. See this Using HeapDumpOnOutOfMemoryError parameter for heap dump for JBoss

Then, fire the exception running your code.

Last thing is to analyze the dump with a tool like Eclipse Memory Analyzer https://eclipse.org/mat/ and look for big objects o a big number of instances of small objects. There are lots of tutorials about how to analyze a memory dump: http://www.vogella.com/tutorials/EclipseMemoryAnalyzer/article.html

score 0 · Answer 3 · answered Aug 04 '15 at 13:01

0

Basically in snippet 2 at the beginning you just initialize the map2 for nothing. After second step it will just point to another address and older one will be garbage collected.

answered Aug 04 '15 at 13:01

quadruplecroche

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Uninitialized object vs new object

3 Answers3