Class used as a null placeholder where {@code null}has another meaning.
For example, in a {@code HashMap} the{@link java.util.HashMap#get(java.lang.Object)} method returns{@code null} if the {@code Map} contains {@code null} or if there isno matching key. The {@code Null} placeholder can be used to distinguishbetween these two cases.
Another example is {@code Hashtable}, where {@code null}cannot be stored.
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|