Almost all the programming languages are bonded with null. There is hardly a programmer, who is not troubled by null.
In Java, null is associated java.lang.NullPointerException. As it is a class in java.lang package, it is called when we try to perform some operations with or without null and sometimes we don’t even know where it has happened.
Below are some important points about null in java which every Java programmer should know:
1. null is Case sensitive: null is literal in Java and because keywords are case-sensitive in java, we can’t write NULL or 0 as in C language.
5: error: cannot find symbol can't find symbol 'NULL' ^ variable NULL class Test 1 error
2. Reference Variable value: Any reference variable in Java has default value null.
Value of object obj is : null
3. Type of null: Unlike common misconception, null is not Object or neither a type. It’s just a special value, which can be assigned to any reference type and you can type cast null to any type
// null can be assigned to String String str = null; // you can assign null to Integer also Integer itr = null; // null can also be assigned to Double Double dbl = null; // null can be type cast to String String myStr = (String) null; // it can also be type casted to Integer Integer myItr = (Integer) null; // yes it's possible, no error Double myDbl = (Double) null;
4. Autoboxing and unboxing : During auto-boxing and unboxing operations, compiler simply throws Nullpointer exception error if a null value is assigned to primitive boxed data type.
Exception in thread "main" java.lang.NullPointerException at Test.main(Test.java:6)
5. instanceof operator: The java instanceof operator is used to test whether the object is an instance of the specified type (class or subclass or interface). At run time, the result of the instanceof operator is true if the value of the Expression is not null.
This is an important property of instanceof operation which makes it useful for type casting checks.
6. Static vs Non static Methods: We cannot call a non-static method on a reference variable with null value, it will throw NullPointerException, but we can call static method with reference variables with null values. Since static methods are bonded using static binding, they won’t throw Null pointer Exception.
static method, can be called by null referenceException in thread "main" java.lang.NullPointerException at Test.main(Test.java:5)
7. == and != The comparison and not equal to operators are allowed with null in Java. This can made useful in checking of null with objects in java.
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