Java Collections unmodifiableMap() Method with Examples

by Online Tutorials Library July 22, 2022

Java Collections unmodifiableMap() Method

The unmodifiableMap() method of Java Collections class is used to get an unmodifiable view of the specified map.

Syntax

Following is the declaration of unmodifiableMap() method:

Parameter

Parameter	Description	Required/Optional
m	It is the map for which an unmodifiable view is to be returned.	Required

Returns

The unmodifiableMap() method returns an unmodifiable view of the specified map.

Exceptions

Example 1

  import java.util.*;  public class CollectionsUnmodifiableMapExample1 {      public static void main(String[] args) {        //Create object of hash map and Add values in the map          HashMap<String,String> map = new HashMap<String,String>();          map.put(“key1”, “Java”);          map.put(“key2”, “Android”);          map.put(“key3”, “JavaScript”);          System.out.println(“Initial collection: “+map);          //Create unmodifiable map          Map<String,String> map2 = Collections.unmodifiableMap(map);          System.out.println(“Unmodifiable Map: ” + map2);                 map.put(“key4”, “TutorAspire”);          System.out.println(“Unmodifiable Map after adding: ” + map2);          }  }  

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Output:

Initial collection: {key1=Java, key2=Android, key3=JavaScript}  Unmodifiable Map: {key1=Java, key2=Android, key3=JavaScript}  Unmodifiable Map after adding: {key1=Java, key2=Android, key3=JavaScript, key4=TutorAspire}

Example 2

  import java.util.*;  public class CollectionsUnmodifiableMapExample2 {      public static void main(String[] args) {        Map<Integer, String> map = new HashMap<>();          map.put(1, “one”);          map.put(2, “two”);          System.out.println(“Initial Unmodifiable Map: “+map);          Map<Integer, String> map2 = Collections.unmodifiableMap(map);          map2.put(3, “three”);          }  }  

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Output:

Initial Unmodifiable Map: {1=one, 2=two}  Exception in thread "main" java.lang.UnsupportedOperationException  at java.base/java.util.Collections$UnmodifiableMap.put(Collections.java:1453)  at myPackage.CollectionsUnmodifiableMapExample2.main(CollectionsUnmodifiableMapExample2.java:10)

Example 3

  import java.util.*;  public class CollectionsUnmodifiableMapExample3 {  public static void main(String[] args) {  Map<Integer, Integer> map = new HashMap<>();  map.put(1, 1001);  map.put(2, 1002);  map.put(3, 1003);  map.put(4, 1004);  map.put(5, 1005);  System.out.println(“Unmodifiable map: ” + map);  Map<Integer, Integer> map2 = Collections.unmodifiableMap(map);        map.remove(4, 1004);                     System.out.print(“Unmodifiable map after remove(4, 1004): “+map2);        }  }  

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Output:

Unmodifiable map: {1=1001, 2=1002, 3=1003, 4=1004, 5=1005}  Unmodifiable map after remove(4, 1004): {1=1001, 2=1002, 3=1003, 5=1005}

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Java Collections unmodifiableMap() Method with Examples

Java Collections unmodifiableMap() Method

Syntax

Parameter

Returns

Exceptions

Example 1

Example 2

Example 3

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