Compare two objects in Java with possible null values

Question

I want to compare two strings for equality when either or both can be null  So  I can t simply call  equals   as it can contain null values  The code I have tried so far   boolean compare String str1  String str2      return   str1    str2      str1    null  amp  amp  str1 equals str2        What will be the best way to check for all possible values including null

User · Accepted Answer

This is what Java internal code uses  on other compare methods    public static boolean compare String str1  String str2        return  str1    null   str2    null   str1 equals str2

User · Answer

Since version 3 5 Apache Commons StringUtils has the following methods   static int  compare String str1  String str2  static int  compare String str1  String str2  boolean nullIsLess  static int  compareIgnoreCase String str1  String str2  static int  compareIgnoreCase String str1  String str2  boolean nullIsLess    These provide null safe String comparison

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Using Java 8   private static Comparator lt String gt  nullSafeStringComparator   Comparator          nullsFirst String  compareToIgnoreCase     private static Comparator lt Metadata gt  metadataComparator   Comparator          comparing Metadata  getName  nullSafeStringComparator           thenComparing Metadata  getValue  nullSafeStringComparator    public int compareTo Metadata that        return metadataComparator compare this  that

User · Answer

For these cases it would be better to use Apache Commons StringUtils equals  it already handles null strings  Code sample   public boolean compare String s1  String s2        return StringUtils equals s1  s2       If you dont want to add the library  just copy the source code of the StringUtils equals method and apply it when you need it

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OK  so what does  best possible solution  mean   If you mean most readable  then all the possible solutions are pretty much equivalent for an experienced Java programmer   But IMO the most readable is this   public boolean compareStringsOrNulls String str1  String str2            Implement it how you like      In other words  hide the implementation inside a simple method that  ideally  can be inlined    You could also  out-source  to a 3rd party utility library     if you already use it in your codebase      If you mean most performant  then    the most performant solution depends on the platform and the context   one of the  context  issues is the relative  dynamic  frequency of occurrence of null arguments  it probably doesn t matter which version is faster     because the difference is probably too small to make a difference to the overall application performance  and if it does matter  the only way to figure out which is fastest ON YOUR PLATFORM is to try both versions and measure the difference

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For those on android  who can t use API 19 s Objects equals str1  str2   there is this   android text TextUtils equals str1  str2     It is null safe   It rarely has to use the more expensive string equals   method because identical strings on android almost always compare true with the      operand thanks to Android s String Pooling  and length checks are a fast way to filter out most mismatches   Source Code          Returns true if a and b are equal  including if they are both null      lt p gt  lt i gt Note  In platform versions 1 1 and earlier  this method only worked  well if    both the arguments were instances of String  lt  i gt  lt  p gt      param a first CharSequence to check     param b second CharSequence to check     return true if a and b are equal     public static boolean equals CharSequence a  CharSequence b        if  a    b  return true      int length      if  a    null  amp  amp  b    null  amp  amp   length   a length       b length              if  a instanceof String  amp  amp  b instanceof String                return a equals b             else               for  int i   0  i  lt  length  i                      if  a charAt i     b charAt i   return false                            return true                      return false

User · Answer

boolean compare String str1  String str2        if  str1    null    str2    null          return str1    str2       return str1 equals str2

User · Answer

You can use  java util Objects as following   public static boolean compare String str1  String str2        return Objects equals str1  str2

User · Answer

boolean compare String str1  String str2        if str1  null    str2  null              return false  if you assume null not equal to null         return str1  str2            return str1 equals str2       is this what you desired

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boolean compare String str1  String str2      return  str1  null    str2  null    str1    str2   str1 equals str2

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Compare two string using equals - -  and equalsIgnoreCase - -  method of Apache Commons StringUtils class   StringUtils equals -  -     StringUtils equals null  null      true StringUtils equals null   abc      false StringUtils equals  abc   null     false StringUtils equals  abc    abc     true StringUtils equals  abc    ABC     false   StringUtils equalsIgnoreCase -  -     StringUtils equalsIgnoreCase null  null      true StringUtils equalsIgnoreCase null   abc      false StringUtils equalsIgnoreCase  xyz   null     false StringUtils equalsIgnoreCase  xyz    xyz     true StringUtils equalsIgnoreCase  xyz    XYZ     true

User · Answer

Since Java 7 you can use the static method java util Objects equals Object  Object  to perform equals checks on two objects without caring about them being null   If both objects are null it will return true  if one is null and another isn t it will return false  Otherwise it will return the result of calling equals on the first object with the second as argument

[java] Compare two objects in Java with possible null values

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