Java Object Null Check for method

Question

I need to create a null check in this formula for the books i  and I am not entirely sure how to go about this as I am not greatly familiar with null checks and very new at programming  Any and all help is much appreciated   public static double calculateInventoryTotal Book   books        double total   0       for  int i   0  i  lt  books length  i                  total    books i  getPrice               return total

User · Answer

If you are using Java 7 You can use Objects requireNotNull object   optionalMessage    - to check if the parameter is null  To check if each element is not null just use  if null    books i     do stuff      Example    public static double calculateInventoryTotal Book   books       Objects requireNotNull books   Books must not be null         double total   0       for  int i   0  i  lt  books length  i             if null    book i                total    books i  getPrice                         return total

User · Answer

First you should check if books itself isn t null  then simply check whether books i     null   if books  null  throw new IllegalArgumentException     for  int i   0  i  lt  books length  i        if books i     null           total    books i  getPrice

User · Answer

Inside your for-loop  just add the following line   if books i     null         total    books i  getPrice

User · Answer

This question is quite older  The Questioner might have been turned into an experienced Java Developer by this time  Yet I want to add some opinion here which would help beginners   For JDK 7 users  Here using   Objects requireNotNull object   optionalMessage      is not safe  This function throws NullPointerException if it finds null object and which is a RunTimeException   That will terminate the whole program    So better check null using    or      Also  use List instead of Array  Although access speed is same  yet using Collections over Array has some advantages like if you ever decide to change the underlying implementation later on  you can do it flexibly  For example  if you need synchronized access  you can change the implementation to a Vector without rewriting all your code   public static double calculateInventoryTotal List lt Book gt  books        if  books    null    books isEmpty              return 0             double total   0       for  Book book   books            if  book    null                total    book getPrice                        return total      Also  I would like to upvote  1ac0 answer  We should understand and consider the purpose of the method too while writing  Calling method could have further logics to implement based on the called method s returned data   Also if you are coding with JDK 8  It has introduced a new way to handle null check and protect the code from NullPointerException  It defined a new class called Optional  Have a look at this for detail  Finally  Pardon my bad English

User · Answer

You simply compare your object to null using the     or     operator  E g    public static double calculateInventoryTotal Book   books           First null check - the entire array     if  books    null            return 0             double total   0       for  int i   0  i  lt  books length  i                 second null check - each individual element         if  books i     null                total    books i  getPrice                         return total

User · Answer

If array of Books is null  return zero as it looks that method count total price of all Books provided - if no Book is provided  zero is correct value   public static double calculateInventoryTotal Book   books    if books    null  return 0      double total   0      for  int i   0  i  lt  books length  i                  total    books i  getPrice              return total      It s upon to you to decide if it s correct that you can input null input value  shoul not be correct  but

User · Answer

public static double calculateInventoryTotal Book   arrayBooks         final AtomicReference lt BigDecimal gt  total   new AtomicReference lt  gt  BigDecimal ZERO       Optional ofNullable arrayBooks  map Arrays  asList  ifPresent books - gt  books forEach book - gt  total accumulateAndGet book getPrice    BigDecimal  add         return total get   doubleValue

User · Answer

You can add a guard condition to the method to ensure books is not null and then check for null when iterating the array   public static double calculateInventoryTotal Book   books        if books    null           throw new IllegalArgumentException  Books cannot be null               double total   0       for  int i   0  i  lt  books length  i                  if books i     null               total    books i  getPrice                         return total

[java] Java Object Null Check for method

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