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?
An empty string is a string instance of zero length, whereas a null string has no value at all. An empty string is represented as "" . It is a character sequence of zero characters. A null string is represented by null .
Null has a default value 0. it can be used as bool,integer, pointer. But C# null is used when we are not pointing to some object.
The String. valueOf(Object) method, as its Javadoc-generated documentation states, returns "null" if the passed in object is null and returns the results on the passed-in Object 's toString() call if the passed-in Object is not null.
“A null String is Java is literally equal to a reserved word “null”. It means the String that does not point to any physical address.” In Java programming language, a “null” String is used to refer to nothing. It also indicates that the String variable is not actually tied to any memory location.
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"
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.
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