why null is not allowed in hashtable?
121506
The reason for allowing only one null key is because keys in a HashMap has to be unique. On the other hand Hashtable does not allow null keys. This is because the objects used as keys in a Hashtable implements the hashCode() and equals() methods for their storage and retrieval.
338470
In Java, the java. lang. NullPointerException is thrown when a reference variable is accessed (or de-referenced) and is not pointing to any object. This error can be resolved by using a try-catch block or an if-else condition to check if a reference variable is null before dereferencing it.
300656
An empty string, however, is a value - it is a string of no characters. Null is essentially 'nothing' - it's the default 'value' (to use the term loosely) that Java assigns to any Object variable that was not initialized. Null isn't really a value - and as such, doesn't have properties.
184840
The SQL NULL is the term used to represent a missing value. A NULL value in a table is a value in a field that appears to be blank. A field with a NULL value is a field with no value. It is very important to understand that a NULL value is different than a zero value or a field that contains spaces.
1419535
According to the Java spec, null is a type that can be assigned to an object variable (as a value as noted in the comment). You cannot instantiate or create variables of this type though, you must use the literal null provided by the compiler. Absolutely not: null instanceof Object returns false.
912681
A hashtable is a dictionary; it stores and retrieves objects by a key value. A vector, on the other hand, holds an ordered collection of elements. It's essentially a dynamic array. Both of these, however, have more subtle characteristics in common.
1143017
It is very important to understand that a NULL value is different than a zero value or a field that contains spaces, spaces are considered as values because they are strings (and sql can't tell what the value of a string means to the user per se), but a NULL signifies a missing value, and hence has no value associated ...
1350364
Parse() and Convert. ToInt32 allows null value, it doesn't throw any errors Int. ... parse does not allow null value, and it throws an ArgumentNullException error.
533828
The main reason that null is not allowed in ConcurrentMaps such as ConcurrentHashMaps, ConcurrentSkipListMaps is to avoid ambiguities. ... In a non-concurrent map, you may check this using map. contains(key), but in a concurrent environment, the map might have changed between calls.
581316
4 Answers. NULL is an absence of a value. An empty string is a value, but is just empty. ... NULL isn't allocated any memory, the string with NULL value is just a pointer which is pointing to nowhere in memory.
1276259
Nil is used to represent a null pointer to an Objective-C class. NULL is used to represent a null pointer to anything else. All these, happen to have the numeric value of 0. They're all zero, but "NULL" is a void *, "nil" is an id, and "Nil" is a Class pointer.
241696
A bit-field shall not be a static member. They are allowed only as struct or union fields there to begin with.
1435420
If several references point to same String without even knowing it, it would be bad if one of the references modified that String value. That's why String objects are immutable.
839321
Operation: LinkedHashMap does a mapping of keys to values while LinkedHashSet simply stores a collection of things. Null Object: LinkedHashMap have elements in key value pair so have only one null key and multiple null value, while LinkedHashSet simply stores a collection of things with one null value.
235926
Nullable types are neither value types nor reference types. They are more like value types, but have a few properties of reference types. Naturally, nullable types may be set to null . Furthermore, a nullable type cannot satisfy a generic struct constraint.
1090753
In Java, int is a primitive type and it is not considered an object. Only objects can have a null value. So the answer to your question is no, it can't be null. ... Depending on your check method, you could be returning an int or an Integer.
107708
Null is the value of reference variable. But empty string is blank.It gives the length=0 . Empty string is a blank value,means the string does not have any thing. No method can be invoked on a object which is assigned a NULL value.