Compare Two HashMap Objects in Java - GeeksforGeeks

04 Jan, 2021
In this article, we will learn how to compare two HashMap objects in Java. In java.util package HashMap class is present. HashMap is used to store key-value pairs, so there are different scenarios to compare two Objects of HashMap. Which is the following:
Compare EntryCompare KeysCompare Values
Compare Entry
Compare Keys
Compare Values
Example:
Input : HashMapA = [a=1, b=2], HashMapB = [a=1, c=2]
Output:
    Compare Entry = Not Equal
    Compare Keys = Not Equal
    Compare values = Equal
1. Compare Entry:
Entry is a key-value pair. We can compare two HashMap by comparing Entry with the equals() method of the Map returns true if the maps have the same key-value pairs that mean the same Entry. 
Below is the implementation:
Java
// Java program to compare two HashMap objectsimport java.util.*;  class GFG {    public static void main(String[] args)    {          // New HashMap1        HashMap<Integer, String> map1 = new HashMap<>();          // Add Entry to map        map1.put(1, "Akshay");        map1.put(2, "Bina");        map1.put(3, "Chintu");          // New HashMap2        HashMap<Integer, String> map2 = new HashMap<>();          // Add Entry to map        map2.put(3, "Chintu");        map2.put(2, "Bina");        map2.put(1, "Akshay");          // New HashMap3        HashMap<Integer, String> map3 = new HashMap<>();          // Add Entry to map        map3.put(1, "Akshay");        map3.put(2, "Binod");        map3.put(3, "Chintu");          // Compare map1 and map2        System.out.println("map1 == map2 : "                           + map1.equals(map2));          // Compare map1 and map3        System.out.println("map1 == map3 : "                           + map1.equals(map3));    }}
map1 == map2 : true
map1 == map3 : false
2. Compare Keys:
We can check if two HashMap objects have the same keys by comparing their keys obtained using the keySet() method. We use equals() method of the set to compare keys.
Below is the implementation:
Java
// Java program to compare two HashSet keysimport java.util.*;  class GFG {    public static void main(String[] args)    {          // New HashMap1        HashMap<Integer, String> map1 = new HashMap<>();          // Add Entry to map        map1.put(1, "Akshay");        map1.put(2, "Bina");        map1.put(3, "Chintu");          // New HashMap2        HashMap<Integer, String> map2 = new HashMap<>();          // Add Entry to map        map2.put(3, "Chintu");        map2.put(2, "Bina");        map2.put(1, "Akshay");          // New HashMap3        HashMap<Integer, String> map3 = new HashMap<>();          // Add Entry to map        map3.put(1, "Akshay");        map3.put(2, "Binod");        map3.put(4, "Chintu");          // Compare map1 and map2 keys using keySet() and        // equals() method        System.out.println(            "map1 keys == map2 keys : "            + map1.keySet().equals(map2.keySet()));          // Compare map1 and map3 keys using keySet() and        // equals() method        System.out.println(            "map1 keys == map3 keys : "            + map1.keySet().equals(map3.keySet()));    }}
map1 keys == map2 keys : true
map1 keys == map3 keys : false
3. Compare Values:
We can compare if values contained in the map objects are the same or not by converting all map values to set using values() method and then compare values with the equals() method of the set. 
Below is the implementation:
Java
// Java program to compare HashMap valuesimport java.util.*;  class GFG {    public static void main(String[] args)    {          // New HashMap1        HashMap<Integer, String> map1 = new HashMap<>();          // Add Entry to map        map1.put(1, "Akshay");        map1.put(2, "Bina");        map1.put(3, "Chintu");          // New HashMap2        HashMap<Integer, String> map2 = new HashMap<>();          // Add Entry to map        map2.put(3, "Chintu");        map2.put(2, "Bina");        map2.put(1, "Akshay");          // New HashMap3        HashMap<Integer, String> map3 = new HashMap<>();          // Add Entry to map        map3.put(1, "Akshay");        map3.put(2, "Binod");        map3.put(3, "Shinchain");          // Value set of map1        HashSet<String> set1 = new HashSet<>(map1.values());          // Value set of map2        HashSet<String> set2 = new HashSet<>(map2.values());          // Value set of map3        HashSet<String> set3 = new HashSet<>(map3.values());          // Compare map1 and map2 values using equals()        // method        System.out.println("map1 values == map2 values : "                           + set1.equals(set2));          // Compare map1 and map3 values using equals()        // method        System.out.println("map1 values == map3 values : "                           + set1.equals(set3));    }}
map1 values == map2 values : true
map1 values == map3 values : false
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