- Java.util Package Classes
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- Java.util - Observable
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- Java.util - PropertyPermission
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- Java.util - Stack
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- Java.util - WeakHashMap
- Java.util Package Extras
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- Java.util - Enumerations
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- Java.util - Discussion
Java Collections unmodifiableMap() Method
Description
The Java Collections unmodifiableMap() method is used to return an unmodifiable view of the specified map.
Declaration
Following is the declaration for java.util.Collections.unmodifiableMap() method.
public static <K,V> Map<K,V> unmodifiableMap(Map<? extends K,? extends V> m)
Parameters
m − This is the map for which an unmodifiable view is to be returned.
Return Value
The method call returns an unmodifiable view of the specified map.
Exception
NA
Getting Immutable Map From a Mutable Map of String, Integer Example
The following example shows the usage of Java Collection unmodifiableMap(Map) method. We've created a Map object of String and Integer. Few entries are added and then using unmodifiableMap(Map) method, we've retrieved the immutable version of map and printed the map.
package com.tutorialspoint; import java.util.Collections; import java.util.HashMap; import java.util.Map; public class CollectionsDemo { public static void main(String[] args) { // create map Map<String,Integer> map = new HashMap<String,Integer>(); // populate the map map.put("1",1); map.put("2",2); map.put("3",3); // create a immutable map Map<String,Integer> immutableMap = Collections.unmodifiableMap(map); System.out.println("Immutable map is :"+immutableMap); } }
Output
Let us compile and run the above program, this will produce the following result.
Immutable map is :{1=1, 2=2, 3=3}
Getting Immutable Map From a Mutable Map of String, String Example
The following example shows the usage of Java Collection unmodifiableMap(Map) method. We've created a Map object of String and String. Few entries are added and then using unmodifiableMap(Map) method, we've retrieved the immutable version of map and printed the map.
package com.tutorialspoint; import java.util.Collections; import java.util.HashMap; import java.util.Map; public class CollectionsDemo { public static void main(String[] args) { // create map Map<String,String> map = new HashMap<String,String>(); // populate the map map.put("1","TP"); map.put("2","IS"); map.put("3","BEST"); // create a immutable map Map<String,String> immutableMap = Collections.unmodifiableMap(map); System.out.println("Immutable map is :"+immutableMap); } }
Output
Let us compile and run the above program, this will produce the following result.
Immutable map is :{1=TP, 2=IS, 3=BEST}
Getting Immutable Map From a Mutable Map of String, Object Example
The following example shows the usage of Java Collection unmodifiableMap(Map) method. We've created a Map object of String and Student object. Few entries are added and then using unmodifiableMap(Map) method, we've retrieved the immutable version of map and printed the map.
package com.tutorialspoint; import java.util.Collections; import java.util.HashMap; import java.util.Map; public class CollectionsDemo { public static void main(String[] args) { // create map Map<String,Student> map = new HashMap<String,Student>(); // populate the map map.put("1",new Student(1, "Julie")); map.put("2",new Student(2, "Robert")); map.put("3",new Student(3, "Adam")); // create a immutable map Map<String,Student> immutableMap = Collections.unmodifiableMap(map); System.out.println("Immutable map is :"+immutableMap); } } class Student { int rollNo; String name; Student(int rollNo, String name){ this.rollNo = rollNo; this.name = name; } @Override public String toString() { return "[ " + this.rollNo + ", " + this.name + " ]"; } }
Output
Let us compile and run the above program, this will produce the following result.
Immutable map is :{1=[ 1, Julie ], 2=[ 2, Robert ], 3=[ 3, Adam ]}
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