Looks up a String key to a String value.

The internal implementation may use any mechanism to return the value. The simplest implementation is to use a Map. However, virtually any implementation is possible.

For example, it would be possible to implement a lookup that used the key as a primary key, and looked up the value on demand from the database Or, a numeric based implementation could be created that treats the key as an integer, increments the value and return the result as a string - converting 1 to 2, 15 to 16 etc.

The lookup(String) method always returns a String, regardless of the underlying data, by converting it as necessary. For example:

Map<String, Object> map = new HashMap<String, Object>();
map.put("number", Integer.valueOf(2));
assertEquals("2", StrLookup.mapLookup(map).lookup("number"));

Parameters

key:String

the key to be looked up, may be null.

Returns:String

the matching value, null if no match.

Returns a lookup which looks up values using a map.

If the map is null, then null will be returned from every lookup. The map result object is converted to a string using toString().

Parameters

<V>

the type of the values supported by the lookup.

map:Map<String, V>

the map of keys to values, may be null.

Returns:StrLookup<V>

a lookup using the map, not null.

Returns a lookup which always returns null.

Returns:StrLookup<?>

a lookup that always returns null, not null.

Returns a new lookup which uses a copy of the current System properties.

If a security manager blocked access to system properties, then null will be returned from every lookup.

If a null key is used, this lookup will throw a NullPointerException.

Returns:StrLookup<String>

a lookup using system properties, not null.