HashMap to return default value for non-found keys?

Question

Is it possible to have a HashMap return a default value for all keys that are not found in the set?

Answer 1

I needed to read the results returned from a server in JSON where I couldn't guarantee the fields would be present. I'm using class org.json.simple.JSONObject which is derived from HashMap. Here are some helper functions I employed:

public static String getString( final JSONObject response, 
                                final String key ) 
{ return getString( response, key, "" ); }  
public static String getString( final JSONObject response, 
                                final String key, final String defVal ) 
{ return response.containsKey( key ) ? (String)response.get( key ) : defVal; }

public static long getLong( final JSONObject response, 
                            final String key ) 
{ return getLong( response, key, 0 ); } 
public static long getLong( final JSONObject response, 
                            final String key, final long defVal ) 
{ return response.containsKey( key ) ? (long)response.get( key ) : defVal; }

public static float getFloat( final JSONObject response, 
                              final String key ) 
{ return getFloat( response, key, 0.0f ); } 
public static float getFloat( final JSONObject response, 
                              final String key, final float defVal ) 
{ return response.containsKey( key ) ? (float)response.get( key ) : defVal; }

public static List getList( final JSONObject response, 
                                        final String key ) 
{ return getList( response, key, new ArrayList() ); }   
public static List getList( final JSONObject response, 
                                        final String key, final List defVal ) { 
    try { return response.containsKey( key ) ? (List) response.get( key ) : defVal; }
    catch( ClassCastException e ) { return defVal; }
}