in my project ,Somewhere I have to use if n else condition to check the null variables
String stringValue = null;
String valueOf = String.valueOf(stringValue);
but when i check the condition like
if (valueOf == null) {
System.out.println("in if");
} else {
System.out.println("in else");
}
then output is "in else" ,why this is happening?
Here's the source code of String.valueOf: -
public static String valueOf(Object obj) {
return (obj == null) ? "null" : obj.toString();
}
As you can see, for a null value it returns "null" string.
So,
String stringValue = null;
String valueOf = String.valueOf(stringValue);
gives "null" string to the valueOf.
Similarly, if you do: -
System.out.println(null + "Rohit");
You will get: -
"nullRohit"
EDIT
Another Example:
Integer nulInteger = null;
String valueOf = String.valueOf(nulInteger) // "null"
But in this case.
Integer integer = 10;
String valueOf = String.valueOf(integer) // "10"
null is an empty object, whereas "null" is an actual string containing the characters 'n', 'u', 'l', and 'l'.
"null". So a null will not be equal to "null" literal.
null to "null" string does not happens always, but only in certain pre-defined cases. Like in case of String Concatenation - As defined in JLS - String Concatenation. However, it is not defined for String Comparison.Actually, you can have a look at the implementation of the method: valueOf(). You will know what happened then.
In JDK 1.5, its code is like this:
public static String valueOf(Object obj) {
return (obj == null) ? "null" : obj.toString();
}
From the code, you can see that if the object is null it will return a not null string with "null" value in it, which means the valueOf object is not null.
