How to compare two maps by their values

Question

How to compare two maps by their values  I have two maps containing equal values and want to compare them by their values  Here is an example       Map a   new HashMap        a put  foo    bar   bar        a put  zoo    bar   bar         Map b   new HashMap        b put new String  foo     bar   bar        b put new String  zoo     bar   bar         System out println  equals      a equals b                  obviously false   How should I change the code to obtain a true

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public boolean equalMaps Map lt      gt  map1  Map lt      gt map2         if  map1  null    map2  null    map1 size      map2 size              return false             for  Object key  map1 keySet              if   map1 get key  equals map2 get key                  return false                      return true

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The correct way to compare maps for value-equality is to    Check that the maps are the same size    Get the set of keys from one map For each key from that set you retrieved  check that the value retrieved from each map for that key is the same  if the key is absent from one map  that s a total failure of equality    In other words  minus error handling    boolean equalMaps Map lt K V gt m1  Map lt K V gt m2       if  m1 size      m2 size          return false     for  K key  m1 keySet          if   m1 get key  equals m2 get key             return false     return true

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This question is old  but still relevant   If you want to compare two maps by their values matching their keys  you can do as follows     public static  lt K  V gt  boolean mapEquals Map lt K  V gt  leftMap  Map lt K  V gt  rightMap        if  leftMap    rightMap  return true      if  leftMap    null    rightMap    null    leftMap size      rightMap size    return false      for  K key   leftMap keySet              V value1   leftMap get key           V value2   rightMap get key           if  value1    null  amp  amp  value2    null              continue          else if  value1    null    value2    null              return false          if   value1 equals value2               return false            return true

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If you assume that there can be duplicate values the only way to do this is to put the values in lists  sort them and compare the lists viz   List lt String gt  values1   new ArrayList lt String gt  map1 values     List lt String gt  values2   new ArrayList lt String gt  map2 values     Collections sort values1   Collections sort values2   boolean mapsHaveEqualValues   values1 equals values2     If values cannot contain duplicate values then you can either do the above without the sort using sets

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I don t think there is a  apache-common-like  tool to compare maps since the equality of 2 maps is very ambiguous and depends on the developer needs and the map implementation     For exemple if you compare two hashmaps in java  - You may want to just compare key values are the same - You may also want to compare if the keys are ordered the same way - You may also want to compare if the remaining capacity is the same     You can compare a lot of things   What such a tool would do when comparing 2 different map implementations such that  - One map allow null keys - The other throw runtime exception on map2 get null   You d better to implement your own solution according to what you really need to do  and i think you already got some answers above

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To see if two maps have the same values  you can do the following    Get their Collection lt V gt  values   views Wrap into List lt V gt  Collections sort those lists Test if the two lists are equals   Something like this works  though its type bounds can be improved on    static  lt V extends Comparable lt V gt  gt  boolean valuesEquals Map lt   V gt  map1  Map lt   V gt  map2        List lt V gt  values1   new ArrayList lt V gt  map1 values         List lt V gt  values2   new ArrayList lt V gt  map2 values         Collections sort values1       Collections sort values2       return values1 equals values2       Test harness   Map lt String  String gt  map1   new HashMap lt String String gt     map1 put  A    B    map1 put  C    D     Map lt String  String gt  map2   new HashMap lt String String gt     map2 put  A    D    map2 put  C    B     System out println valuesEquals map1  map2       prints  true    This is O N log N  due to Collections sort   See also    Collection lt V gt  values       To test if the keys are equals is easier  because they re Set lt K gt    map1 keySet   equals map2 keySet      See also    Set lt K gt  keySet

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If anyone is looking to do it in Java 8 streams below is the example   import java util HashMap  import java util Map   public class CompareTwoMaps        public static void main String   args             Map lt String  String gt  a   new HashMap lt  gt             a put  foo    bar     bar            a put  zoo    bar     bar             Map lt String  String gt  b   new HashMap lt  gt             b put new String  foo     bar     bar            b put new String  zoo     bar     bar             System out println  result       areEqual a  b               private static boolean areEqual Map lt String  String gt  first  Map lt String  String gt  second            return first entrySet   stream                    allMatch e - gt  e getValue   equals second get e getKey

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The result of equals in your example is obviously false because you are comparing the map a with some values in it with an empty map b  probably a copy and paste error   I recommend to use proper variable names  so you can avoid these kinds of errors  and make use of generics  too       Map lt String  String gt  first   new HashMap lt String  String gt         first put  f   oo    bar   bar        first put  fo   o    bar   bar         Map second   new HashMap        second put  f   oo    bar   bar        second put  fo   o    bar   bar         System out println  equals      first equals second      The concatenation of your strings doesn t have any effect because it will be done at compile time

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Since you asked about ready-made Api s     well Apache s commons  collections library has a CollectionUtils class that provides easy-to-use methods for Collection manipulation checking  such as intersection  difference  and union

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All of these are returning equals  They arent actually doing a comparison  which is useful for sort  This will behave more like a comparator   private static final Comparator stringFallbackComparator   new Comparator         public int compare Object o1  Object o2            if    o1 instanceof Comparable               o1   o1 toString            if    o2 instanceof Comparable               o2   o2 toString            return   Comparable o1  compareTo o2             public int compare Map m1  Map m2        TreeSet s1   new TreeSet stringFallbackComparator   s1 addAll m1 keySet         TreeSet s2   new TreeSet stringFallbackComparator   s2 addAll m2 keySet         Iterator i1   s1 iterator        Iterator i2   s2 iterator        int i      while  i1 hasNext    amp  amp  i2 hasNext                  Object k1   i1 next            Object k2   i2 next            if  0   i stringFallbackComparator compare k1  k2                return i          if  0   i stringFallbackComparator compare m1 get k1   m2 get k2                 return i            if  i1 hasNext            return 1      if  i2 hasNext            return -1      return 0

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If you want to compare two Maps then  below code may help you   new TreeMap lt String  Object gt  map1  toString   hashCode       new TreeMap lt String  Object gt  map2  toString   hashCode

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paweloque For Comparing two Map Objects in java  you can add the keys of a map to list and with those 2 lists you can use the methods retainAll   and removeAll   and add them to another common keys list and different keys list  Using the keys of the common list and different list you can iterate through map  using equals you can compare the maps   The below code will give output like this  Before  zoo barbar  foo barbar  After  zoo barbar  foo barbar  Equal  Before- barbar After- barbar Equal  Before- barbar After- barbar   package com demo compareExample  import java util ArrayList  import java util HashMap  import java util Iterator  import java util List  import java util Map   import org apache commons collections CollectionUtils   public class Demo        public static void main String   args                 Map lt String  String gt  beforeMap   new HashMap lt String  String gt             beforeMap put  foo    bar   bar            beforeMap put  zoo    bar   bar             Map lt String  String gt  afterMap   new HashMap lt String  String gt             afterMap put new String  foo     bar   bar            afterMap put new String  zoo     bar   bar             System out println  Before   beforeMap           System out println  After   afterMap            List lt String gt  beforeList   getAllKeys beforeMap            List lt String gt  afterList   getAllKeys afterMap            List lt String gt  commonList1   beforeList          List lt String gt  commonList2   afterList          List lt String gt  diffList1   getAllKeys beforeMap           List lt String gt  diffList2   getAllKeys afterMap            commonList1 retainAll afterList           commonList2 retainAll beforeList            diffList1 removeAll commonList1           diffList2 removeAll commonList2            if commonList1  null  amp  commonList2  null     athough both the size are same                       for  int i   0  i  lt  commonList1 size    i                                   if   beforeMap get commonList1 get i    equals afterMap get commonList1 get i                                            System out println  Equal  Before-    beforeMap get commonList1 get i     After-   afterMap get commonList1 get i                                       else                                       System out println  Unequal  Before-    beforeMap get commonList1 get i     After-   afterMap get commonList1 get i                                                       if  CollectionUtils isNotEmpty diffList1                          for  int i   0  i  lt  diffList1 size    i                                   System out println  Values present only in before map    beforeMap get diffList1 get i                                     if  CollectionUtils isNotEmpty diffList2                          for  int i   0  i  lt  diffList2 size    i                                   System out println  Values present only in after map    afterMap get diffList2 get i                                           getAllKeys API adds the keys of the map to a list        private static List lt String gt  getAllKeys Map lt String  String gt  map1                List lt String gt  key   new ArrayList lt String gt             if  map1    null                         Iterator lt String gt  mapIterator   map1 keySet   iterator                while  mapIterator hasNext                                   key add mapIterator next                                     return key

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Your attempts to construct different strings using concatenation will fail as it s being performed at compile-time  Both of those maps have a single pair  each pair will have  foo  and  barbar  as the key value  both using the same string reference   Assuming you really want to compare the sets of values without any reference to keys  it s just a case of   Set lt String gt  values1   new HashSet lt  gt  map1 values     Set lt String gt  values2   new HashSet lt  gt  map2 values     boolean equal   values1 equals values2     It s possible that comparing map1 values   with map2 values   would work - but it s also possible that the order in which they re returned would be used in the equality comparison  which isn t what you want   Note that using a set has its own problems - because the above code would deem a map of   a   0    b   0   and   c   0   to be equal    the value sets are equal  after all   If you could provide a stricter definition of what you want  it ll be easier to make sure we give you the right answer

[java] How to compare two maps by their values

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