9 Things Nearly Goose Egg Inwards Java

Java in addition to nothing are uniquely bonded. There is hardly a Java programmer, who is non troubled past times nothing pointer exception, it is the most infamous fact about. Even inventor of nothing concept has called it his billion dollar mistake, in addition to hence why Java kept it? Null was at that topographic point from long fourth dimension in addition to I believe Java designer knows that nothing creates to a greater extent than work than it solves, but nevertheless they went alongside it. It surprise me fifty-fifty to a greater extent than because Java's pattern philosophy was to simplify things, that's why they didn't bothered alongside pointers, operator overloading in addition to multiple inheritance of implementation, they why null. Well I actually don't know the respond of that question, what I know is that, doesn't affair how much nothing is criticized past times Java developers in addition to opened upwards source community, nosotros receive got to alive alongside that. Instead of ruing near nothing it's improve to acquire to a greater extent than near it in addition to brand certain nosotros purpose it correct. Why you lot should acquire near nothing inward Java? because If you lot don't pay attending to null, Java volition brand certain that you lot volition endure from dreaded java.lang.NullPointerException in addition to you lot volition acquire your lesson difficult way. Robust programming is an fine art in addition to your team, client in addition to user volition appreciate that. In my experience, ane of the main reasons of NullPointerException are non plenty noesis near nothing inward Java. Many of you lot already familiar alongside nothing but for those, who are not, tin acquire some onetime in addition to novel things near nothing keyword. Let's revisit or acquire some of import things near nothing inward Java.

What is Null inward Java

As I said, nothing is rattling very of import concept inward Java. It was originally invented to announce absence of something e.g. absence of user, a resources or anything, but over the twelvemonth it has troubled Java programmer a lot alongside nasty nothing pointer exception. In this tutorial, nosotros volition acquire basic facts near nothing keyword inward Java in addition to explore some techniques to minimize nothing checks in addition to how to avoid nasty nothing pointer exceptions.

1) First thing, first,  null is a keyword inward Java, much similar public, static or final. It's representative sensitive, you lot cannot write null as Null or NULL, compiler volition non recognize them in addition to laissez passer on error.

Object obj = NULL; // Not Ok Object obj1 = null  //Ok
 

Programmer's which are coming from other linguistic communication receive got this problem, but purpose of modern 24-hour interval IDE's has made it insignificant. Now days, IDE similar Eclipse or Netbeans tin right this mistake, piece you lot type code, but inward the era of notepad, Vim in addition to Emacs, this was a mutual effect which could easily swallow your precious time.


2) Just similar every primitive has default value e.g. int has 0, boolean has false, null is the default value of whatever reference type, loosely spoken to all object equally well. Just similar if you lot create a boolean variable, it got default value equally false, whatever reference variable inward Java has default value null. This is truthful for all variety of variables e.g. member variable or local variable, instance variable or static variable, except that compiler volition warn you lot if you lot purpose a local variable without initializing them. In enterprise to verify this fact, you lot tin run into value of reference variable past times creating a variable in addition to them printing it's value, equally shown inward next code snippet :

private static Object myObj; public static void main(String args[]){     System.out.println("What is value of myObjc : " + myObj); }   What is value of myObjc : null

This is truthful for both static in addition to non-static object, equally you lot tin run into hither that I made myObj a static reference hence that I tin purpose it direct within principal method, which is static method in addition to doesn't allow non-static variable inside.


3) Unlike mutual misconception, null is non Object or neither a type. It's only a particular value, which tin endure assigned to whatever reference type in addition to you tin type shape nothing to whatever type, equally shown below :

String str = null; // nothing tin endure assigned to String Integer itr = null; // you lot tin assign nothing to Integer also Double dbl = null;  // nothing tin likewise endure assigned to Double          String myStr = (String) null; // nothing tin endure type shape to String Integer myItr = (Integer) null; // it tin likewise endure type casted to Integer Double myDbl = (Double) null; // yeah it's possible, no error

You tin run into type casting nothing to whatever reference type is fine at both compile fourth dimension in addition to runtime, dissimilar many of you lot powerfulness receive got thought, it volition likewise non throw NullPointerException at runtime.


4) nothing tin only endure assigned to reference type, you lot cannot assign nothing to primitive variables e.g. int, double, float or boolean. Compiler volition complain if you lot practice so, equally shown below.

int i = null; // type mismatch : cannot convert from nothing to int short second = null; //  type mismatch : cannot convert from nothing to short byte b = null: // type mismatch : cannot convert from nothing to byte double d = null; //type mismatch : cannot convert from nothing to double          Integer itr = null; // this is ok int j = itr; // this is likewise ok, but NullPointerException at runtime

As you lot tin see, when you lot direct assign nothing to primitive error it's compile fourth dimension error, but if you lot assign nothing to a wrapper degree object in addition to and hence assign that object to respective primitive type, compiler doesn't complain, but you lot would endure greeted past times nothing pointer exception at runtime. This happens because of autoboxing inward Java, in addition to nosotros volition run into it inward side past times side point.


5) Any wrapper degree alongside value nothing volition throw java.lang.NullPointerException when Java unbox them into primitive values. Some programmer makes incorrect supposition that, auto boxing volition bring assist of converting null into default values for respective primitive type e.g. 0 for int, faux for boolean etc, but that's non true, equally seen below.

Integer iAmNull = null; int i = iAmNull; // Remember - No Compilation Error

but when you lot run higher upwards code snippet you lot volition run into Exception inward thread "main" java.lang.NullPointerException  in your console. This happens a lot piece working alongside HashMap in addition to Integer key values. Code similar shown below volition suspension equally before long equally you lot run.

import java.util.HashMap; import java.util.Map;   /**  * An representative of Autoboxing in addition to NullPointerExcpetion  *   * @author WINDOWS 8  */  public class Test {      public static void main(String args[]) throws InterruptedException {                Map numberAndCount = new HashMap<>();        int[] numbers = {3, 5, 7,9, 11, 13, 17, 19, 2, 3, 5, 33, 12, 5};              for(int i : numbers){          int count = numberAndCount.get(i);          numberAndCount.put(i, count++); // NullPointerException here       }            }  }  Output: Exception inward thread "main" java.lang.NullPointerException  at Test.main(Test.java:25)

This code looks rattling uncomplicated in addition to innocuous. All you lot are doing is finding how many times a expose has appeared inward a array, classic technique to observe duplicates inward Java array. Developer is getting the previous count, increasing it past times ane in addition to putting it dorsum into Map. He powerfulness receive got idea that auto-boxing volition bring assist of converting Integer to int , equally it doing piece calling pose method, but he forget that when at that topographic point is no count be for a number, get() method of HashMap volition provide null, non null because default value of Integer is nothing non 0, in addition to auto boxing volition throw nothing pointer exception piece trying to convert it into an int variable. Imagine if this code is within an if loop in addition to doesn't run inward QA environs but equally before long equally you lot pose into production, BOOM :-)


6)instanceof operator volition provide faux if used against whatever reference variable alongside null value or null literal itself, e.g.

Integer iAmNull = null; if(iAmNull instanceof Integer){    System.out.println("iAmNull is instance of Integer");                               }else{    System.out.println("iAmNull is NOT an instance of Integer"); }  Output : iAmNull is NOT an instance of Integer

This is an of import holding of instanceof operation which makes it useful for type casting checks.


7) You may know that you lot cannot telephone phone a non-static method on a reference variable alongside null value, it volition throw NullPointerException, but you lot powerfulness non know that, you lot can call static method alongside reference variables alongside null values. Since static methods are bonded using static binding, they won't throw NPE. Here is an representative :            

public class Testing {                 public static void main(String args[]){       Testing myObject = null;       myObject.iAmStaticMethod();       myObject.iAmNonStaticMethod();                                 }                   private static void iAmStaticMethod(){         System.out.println("I am static method, tin endure called past times nothing reference");    }                   private void iAmNonStaticMethod(){  System.out.println("I am NON static method, don't appointment to telephone phone me past times null");    }   }  Output: I am static method, tin endure called past times null reference Exception inward thread "main" java.lang.NullPointerException                at Testing.main(Testing.java:11)

8) You tin locomote past times null to methods, which accepts whatever reference type e.g. public void print(Object obj) can endure called equally print(null). This is Ok from compiler's shout out for of view, but conduct is solely depends upon method. Null prophylactic method, doesn't throw NullPointerException inward such case, they only locomote out gracefully. It is recommended to write nothing prophylactic method if work concern logic allows.

9) You tin compare nothing value using ==  (equal to ) operator in addition to !=  (not equal to) operator, but cannot purpose it alongside other arithmetics or logical operator e.g. less than or greater than. Unlike inward SQL, inward Java null == null volition provide true, equally shown below :

public class Test {      public static void main(String args[]) throws InterruptedException {                 String abc = null;        String cde = null;                if(abc == cde){            System.out.println("null == nothing is truthful inward Java");        }                if(null != null){            System.out.println("null != nothing is faux inward Java");         }                // classical nothing check        if(abc == null){            // practice something        }                // non ok, compile fourth dimension error        if(abc > null){                    }     } }  Output: null == null is true inward Java

That's all near nothing inward Java. By some sense inward Java coding in addition to past times using simple tricks to avoid NullPointerExcpetion, you lot tin brand your code nothing safe. Since nothing tin endure treated equally empty or uninitialized value it's frequently source of confusion, that's why it's to a greater extent than of import to document conduct of a method for nothing input. Always remember, nothing is default value of whatever reference variable in addition to you lot cannot telephone phone whatever instance method, or access an instance variable using nothing reference inward Java.


Further Learning
Complete Java Masterclass
Java Fundamentals: The Java Language
Java In-Depth: Become a Complete Java Engineer!

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