1. Introduction

In Java, it is possible to create a read-only Map using the Collections.unmodifiableMap() method. A read-only Map is immutable, which means that you cannot modify its content by adding, removing, or altering the elements after it has been created.

2. Program Steps

1. Import the necessary libraries.

2. Create a Map and populate it with key-value pairs.

3. Create a read-only Map using the Collections.unmodifiableMap() method.

4. Attempt to modify the read-only Map and handle the resulting UnsupportedOperationException.

3. Code Program

// Step 1: Import necessary libraries
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;

public class ReadOnlyMapExample {

    public static void main(String[] args) {

        // Step 2: Create a Map and populate it with key-value pairs
        Map<String, String> map = new HashMap<>();
        map.put("1", "Apple");
        map.put("2", "Banana");
        map.put("3", "Cherry");

        // Step 3: Create a read-only Map using Collections.unmodifiableMap()
        Map<String, String> readOnlyMap = Collections.unmodifiableMap(map);

        // Print the read-only map
        System.out.println("Read-only Map: " + readOnlyMap);

        // Step 4: Attempt to modify the read-only Map and handle the resulting UnsupportedOperationException
        try {
            readOnlyMap.put("4", "Dragon Fruit");
        } catch (UnsupportedOperationException e) {
            System.out.println("Exception caught: " + e.getMessage());
        }
    }
}

Output:

Read-only Map: {1=Apple, 2=Banana, 3=Cherry}
Exception caught: null

4. Step By Step Explanation

Step 1: Import the necessary libraries required for handling maps.

Step 2: Create a Map named map and populate it with some key-value pairs representing fruit names.

Step 3: Use the Collections.unmodifiableMap() method to make the map read-only. The resulting readOnlyMap cannot be modified.

Step 4: An attempt to add a new key-value pair to the readOnlyMap throws an UnsupportedOperationException, which is caught and its message is printed to the console.