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/** Assuming the heap size as 512 MB (calculated as 1/4th of 2 GB RAM = 512 MB)
 *  Considering long values being entered (64 bits each, the max number of elements
 *  would be 512 MB/64bits = 67108864)
 */
public class ShowHeapError {
   Vector<Long> names = new Vector<Long>(); // Accepts unknown number of records
   long newID = 0L;
   int count = 67108865;
   int i = 0;
   InputStreamReader input = new InputStreamReader(System.in);
   Scanner reader = new Scanner(input);

   public void addNames() {
     do {
       // Adding unknown number of records to a list
       // The user can enter more IDs than the heap can support and thus 
       // exhaust the heap. Assume that the record ID is a 64 bit long value
      
       System.out.print("Enter recordID (To quit, enter -1): ");
       newID = reader.nextLong();
       
       names.addElement(newID);
       i++;
     }while (i < count || newID != -1);
     // Close "reader" and "input"
   }

   public static void main(String[] args) {
     ShowHeapError demo = new ShowHeapError();
     demo.addNames();
   }
}

Compliant Solution

A simple compliant solution is to lower the number of names to read.

   // ...
   int count = 10000000;
   // ...

Compliant Solution

The {{OutOfMemoryError}} can be avoided by ensuring that the absence of infinite loops, memory leaks, and unnecessary object retention. When memory requirements are known ahead of time, the heap size can be tailored to fit the requirements using the following runtime parameters \[[Java 2006|AA. Bibliography#Java 06]\]:

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This setting can be changed either using the Java Control Panel or from the command line. It cannot be adjusted through the application itself.

Noncompliant Code Example

According to the Java API \[[API 2006|AA. Bibliography#API 06]\], Class {{ObjectInputStream}} documentation

ObjectOutputStream and ObjectInputStream can provide an application with persistent storage for graphs of objects when used with a FileOutputStream and FileInputStream respectively. ObjectInputStream is used to recover the objects previously serialized. Other uses include passing objects between hosts using a socket stream or for marshaling and unmarshaling arguments and parameters in a remote communication system.

By design, objects are written to the stream only on their first appearance therein. For subsequent appearances, the stream writes a handle to the earlier appearance of the object. The ObjectOutputStream maintains a table that maps previously-written objects to their corresponding handles. This table remains live until the stream is closed; consequently, it prevents garbage collection of previously-written objects. This can cause an OutOfMemoryError when streams remain open for extended durations.

FileOutputStream fos = new FileOutputStream("data.txt");
ObjectOutputStream oos = new ObjectOutputStream(fos);
oos.writeObject(new Date());
// ... 

Compliant Solution

Make judicious use of the ObjectOutputStream.reset() method to clear references to previously written objects and consequently permit them to be garbage collected. Note that this will cause subsequent writes of a previously-written object to be treated as though they were the initial write, leading to multiple copies of the object in the serialized data stream. This issue must be addressed to enable correct program operation.

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Risk Assessment

Assuming that infinite heap space is available can result in denial of service.

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