1.7: The null Keyword
- Page ID
- 19649
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When you create an object variable, remember that you are storing a reference to an object. In Java, the keyword null
is a special value that means “no object”. You can declare and initialize object variables this way:
Point blank = null;
The value null
is represented in state diagrams by a small box with no arrow, as in Figure 10.7.1.
If you try to use a null
value, either by accessing an attribute or invoking a method, Java throws a NullPointerException
.
Point blank = null; int x = blank.x; // NullPointerException blank.translate(50, 50); // NullPointerException
On the other hand, it is legal to pass a null reference as an argument or receive one as a return value. For example, null
is often used to represent a special condition or indicate an error.