Limiting the max size of a HashMap in Java

Question

I want to limit the maximum size of a HashMap to take metrics on a variety of hashing algorithms that I'm implementing. I looked at the loadfactor in one of HashMap's overloaded constructors.

HashMap(int initialCapacity, float loadFactor)  

I tried setting the loadFactor to 0.0f in the constructor (meaning that I don't want the HashMap to grow in size EVER) but javac calls this invalid:

Exception in thread "main" java.lang.IllegalArgumentException: Illegal load factor: 0.0         at java.util.HashMap.<init>(HashMap.java:177)         at hashtables.CustomHash.<init>(Main.java:20)         at hashtables.Main.main(Main.java:70) Java Result: 1 

Is there another way to limit the size of HashMap so it doesn't grow ever?

Answer 1

You could create a new class like this to limit the size of a HashMap:

public class MaxSizeHashMap<K, V> extends LinkedHashMap<K, V> {     private final int maxSize;      public MaxSizeHashMap(int maxSize) {         this.maxSize = maxSize;     }      @Override     protected boolean removeEldestEntry(Map.Entry<K, V> eldest) {         return size() > maxSize;     } } 

Answer 2

Sometimes simpler is better.

public class InstrumentedHashMap<K, V> implements Map<K, V> {      private Map<K, V> map;      public InstrumentedHashMap() {         map = new HashMap<K, V>();     }      public boolean put(K key, V value) {         if (map.size() >= MAX && !map.containsKey(key)) {              return false;         } else {              map.put(key, value);              return true;         }     }      ... }