In this code.
public class Test {
public static void testFun(String str) {
if (str == null | str.length() == 0) {
System.out.println("String is empty");
} else {
System.out.println("String is not empty");
}
}
public static void main(String [] args) {
testFun(null);
}
}
We pass a null
value to the function testFun
. Compiles fine, but gives a NullPointerException
in runtime, which I did not expect. Why is it throwing an exception, rather than evaluating the if
condition to true
and printing "String is empty"?
Suppose the value of the actual argument being passed to testFun
is generated from some process. Assume that mistakenly a null
value is returned by that process and is fed to testFun. If such is the case, how does one validate that the value passed to the function is null or not?
One (weird) solution may be by assigning the formal parameter to some variable inside the function and then testing it. But if there are many variables passed to the function, that might become tedious and unfeasible. So, how does one check for null values in such a scenario?
This question is related to
java
nullpointerexception
The problem is that you are using the bitwise or operator: |
. If you use the logical or operator, ||
, your code will work fine.
See also:
http://en.wikipedia.org/wiki/Short-circuit_evaluation
Difference between & and && in Java?
You can use StringUtils
:
import org.apache.commons.lang3.StringUtils;
if (StringUtils.isBlank(str)) {
System.out.println("String is empty");
} else {
System.out.println("String is not empty");
}
Have a look here also: StringUtils.isBlank() vs String.isEmpty()
isBlank
examples:
StringUtils.isBlank(null) = true
StringUtils.isBlank("") = true
StringUtils.isBlank(" ") = true
StringUtils.isBlank("bob") = false
StringUtils.isBlank(" bob ") = false
Change Below line
if (str == null | str.length() == 0) {
into
if (str == null || str.isEmpty()) {
now your code will run corectlly. Make sure str.isEmpty()
comes after str == null
because calling isEmpty()
on null will cause NullPointerException
. Because of Java uses Short-circuit evaluation when str == null
is true it will not evaluate str.isEmpty()
The problem here is that in your code the program is calling 'null.length()' which is not defined if the argument passed to the function is null. That's why the exception is thrown.
The | and & check both the sides everytime.
if (str == null | str.length() == 0)
here we have high possibility to get NullPointerException
Logical || and && check the right hand side only if necessary.
but with logical operator
no chance to get NPE because it will not check RHS
Source: Stackoverflow.com