What is the difference between null, 0 and nothing

问题:

What is the difference between null, 0 and nothing?

I cannot find a question addressing all three of these.

For example:

If I am getting input from a string and parsing it to int.

return Integer.parseInt(sc.nextLine());

Or if I am asking if a string != "", or a is not nothing I am confused about which to use when and why.

I am confused about which one to use when validating data.

回答1:

null means that a variable contains a reference to a space in memory that does not contain an object.

0 is a numeric data type with a value of 0.

Nothing doesn't really exist, however I think you may be viewing this as an empty String "" which is simply a String data type that does not contain a value.

If your looking at this from a Javascript paradigm it may be confusing. In Java variables are not truthy and falsey therefore the type is considered in comparisons.

回答2:

0 is a number, you use it to check if a numeric value (int, short, float, double, etc.) is the number 0.

null is the value of a reference that points nowhere, you use it to make sure a reference does indeed reference something.

nothing is not part of Java.

The closest thing for nothing (for: no information at all) is the void declaration of a method. It states that the method returns literally nothing.

Note that 0, null and the empty string "" are values and thus contain information.

For example, 0 is the answer to "What is 5 subtracted from 5?" (among others).

null is the negative response to "Does this thing point to an object?".

""" could be the answer to "What is the longest sequenc of 'X's in your name?", unless your name is "Xanthippe".

回答3:

There isn't a "nothing" in Java. There is a null reference, meaning that a variable refers to no object, so it is a kind of nothing, but there isn't the concept of undefined as it is in Javascript.

Also, please note that a String comparison should be done using equals, not != or ==, so string.equals(otherString).

The 0 value is the default value that an int gets when declared as an instance variable.

回答4:

"Null" in Java , the object reference is not pointing to any object, it is null.

"Nothing", Java has nothing called "Nothing"

"0" means that .the string object exists with a value of "0"

"" means an empty String ,i.e the String Object exists with value ""

回答5:

• "nothing" means nothing in Java.

• 0 means an integer value greater than -1 and less than 1.

• "Null" means if any Object Reference points nowhere in the memory, then it's called "Null" reference.

回答6:

The best approach to check String objects in Java is using org.apache.commons.lang.StringUtils.

If you do not want to use StringUtils, you might want to check that sc.nextList() is not null (!= null) first of all, if it is not null then you can check that is different from "" (!= "").

回答7:

Null variable isn't assigned any value. The memory space (of variable) is empty or holds garbage value. while a variable is 0, the variable holds the value '0'. The memory space has value '0' stored in it.

NULL basically means no value, or unknown,NULL value could be either empty, meaningless, or not even initialized. For eg when we say, Employee bonus is null, it means the person is not getting any bonus or not eligible for bonus.now in case if value is 0 its mean employee getting bonus but currently bonus is zero.

回答8:

For example:

int s;      //s=null
int s = 0 ;  //s=0
String s="";// s=nothing