Key existence check in HashMap

Question

Is checking for key existence in HashMap always necessary?

I have a HashMap with say a 1000 entries and I am looking at improving the efficiency. If the HashMap is being accessed very frequently, then checking for the key existence at every access will lead to a large overhead. Instead if the key is not present and hence an exception occurs, I can catch the exception. (when I know that this will happen rarely). This will reduce accesses to the HashMap by half.

This might not be a good programming practice, but it will help me reduce the number of accesses. Or am I missing something here?

[Update] I do not have null values in the HashMap.

Answer 1

Do you ever store a null value? If not, you can just do:

Foo value = map.get(key); if (value != null) {     ... } else {     // No such key } 

Otherwise, you could just check for existence if you get a null value returned:

Foo value = map.get(key); if (value != null) {     ... } else {     // Key might be present...     if (map.containsKey(key)) {        // Okay, there's a key but the value is null     } else {        // Definitely no such key     } } 

Answer 2

You won't gain anything by checking that the key exists. This is the code of HashMap:

@Override public boolean containsKey(Object key) {     Entry<K, V> m = getEntry(key);     return m != null; }  @Override public V get(Object key) {     Entry<K, V> m = getEntry(key);     if (m != null) {         return m.value;     }     return null; } 

Just check if the return value for get() is different from null.

This is the HashMap source code.

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Resources :

• HashMap source code Bad one
• HashMap source code Good one