问题
How do you check if a boolean is null or not? So if I know "hideInNav" is null. How do I stop it from further executing? Something like the below doesn't seem to work but why?
boolean hideInNav = parent.getProperties().get("hideInNav", false);
String hideNavigation = hideInNav != null ? hideInNav : "";
回答1:
boolean can only be true or false because it's a primitive datatype (+ a boolean variables default value is false). You can use the class Boolean instead if you want to use null values. Boolean is a reference type, that's the reason you can assign null to a Boolean "variable". Example:
Boolean testvar = null;
if (testvar == null) { ...}
回答2:
A boolean cannot be null in java.
A Boolean, however, can be null.
If a boolean is not assigned a value (say a member of a class) then it will be false by default.
回答3:
In Java, null only applies to object references; since boolean is a primitive type, it cannot be assigned null.
It's hard to get context from your example, but I'm guessing that if hideInNav is not in the object returned by getProperties(), the (default value?) you've indicated will be false. I suspect this is the bug that you're seeing, as false is not equal to null, so hideNavigation is getting the empty string?
You might get some better answers with a bit more context to your code sample.
回答4:
The only thing that can be a null is a non-primivite.
A boolean which can only hold TRUE or FALSE is a primitive. The TRUE/FALSE in memory are actually numbers (0 and 1)
0 = FALSE
1 = TRUE
So when you instantiate an object it will be null
String str; // will equal null
On the other hand if you instaniate a primitive it will be assigned to 0 default.
boolean isTrue; // will be 0
int i; // will be 0
回答5:
boolean is a primitive type, and therefore can not be null.
Its boxed type, Boolean, can be null.
The function is probably returning a Boolean as opposed to a boolean, so assigning the result to a Boolean-type variable will allow you to test for nullity.
回答6:
null is a value assigned to a reference type. null is a reserved value, indicating that a reference does not resemble an instance of an object.
A boolean is not an instance of an Object. It is a primitive type, like int and float. In the same way that: int x has a value of 0, boolean x has a value of false.
来源：https://stackoverflow.com/questions/15937715/java-check-if-boolean-is-null