Converting Integer-String HashMap to String-Array-Integer HashMap in Java
Last Updated :
29 Dec, 2023
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Efficient Conversion of a HashMap<Integer, String> into another HashMap<String, Integer[]> involves organizing integer keys based on their corresponding string values. Here's a concise and efficient Java method to accomplish this transformation, focusing on clear and straightforward implementation.
Step-by-Step Implementation of Conversion
The method follows a step-by-step procedure using HashMaps and Lists.
- First, it gathers integer keys together by looking at their matching string values in a temporary HashMap.
- Then, it turns these grouped keys into arrays, creating a fresh HashMap where strings are linked to arrays of integers.
// Java program for converting a
// HashMap<Integer, String> to HashMap<String, Integer[]>.
import java.util.*;
// Driver class
public class HashMapConversion {
// Main Method
public static void main(String[] args){
// Create an input HashMap with integer keys and
// string values
HashMap<Integer, String> inputMap = new HashMap<>();
inputMap.put(1, "a");
inputMap.put(2, "b");
inputMap.put(3, "a");
inputMap.put(4, "k");
inputMap.put(5, "fg");
inputMap.put(7, "aa");
inputMap.put(9, "b");
inputMap.put(10, "vc");
// Create an output HashMap to store strings as keys
// and lists of associated integer keys
HashMap<String, List<Integer>> outputMap= new HashMap<>();
// Iterate through each entry in the input map
for (Map.Entry<Integer, String> entry:inputMap.entrySet()) {
// Get the integer key
Integer key= entry.getKey();
// Get the string value
String value= entry.getValue();
// Check if the output map already contains the
// string value as a key
if (outputMap.containsKey(value)) {
// If it exists, add the current integer key
// to its associated list
outputMap.get(value).add(key);
}
else {
// If it doesn't exist, create a new list
// for the string value and add the current
// integer key
List<Integer> list = new ArrayList<>();
list.add(key);
outputMap.put(value, list);
}
}
// Create a final HashMap to store strings as keys
// and arrays of associated integer keys
HashMap<String, Integer[]> finalMap= new HashMap<>();
// Iterate through each entry in the output map
// (which has string keys and list values)
for (Map.Entry<String, List<Integer> > entry:outputMap.entrySet()) {
// Get the string key
String key = entry.getKey();
// Get the list of integer values
List<Integer> values= entry.getValue();
// Convert the list of integer values to an
// array and store it in the final map
finalMap.put(key,
values.toArray(new Integer[0]));
}
// Print the final map contents
for (Map.Entry<String, Integer[]> entry:finalMap.entrySet()) {
System.out.print("<" + entry.getKey() + ",[");
// Get the array of integer values
Integer[] values = entry.getValue();
// Print each integer of array
for (int i = 0; i < values.length; i++) {
System.out.print(values[i]);
if (i < values.length - 1) {
System.out.print(",");
}
}
System.out.println("]>");
}
}
}
Output
<aa,[7]> <a,[1,3]> <fg,[5]> <b,[2,9]> <k,[4]> <vc,[10]>
Explanation of the above code:
- This program uses the HashMap where numbers are linked to words and rearranges it.
- It groups numbers based on the words they're linked to, creating arrays for each word with their corresponding numbers.
- For example, the key "a" in the final map has the value
[1, 3]. This means that in the input map, the String value "a" was associated with both the Integer keys 1 and 3.
Conclusion
This method provides an efficient way to convert a HashMap with integer keys and string values to a HashMap with string keys and integer arrays. It leverages temporary HashMaps and Lists for intermediate storage while prioritizing clear and straightforward implementation. The code effectively utilizes Java's built-in data structures and iterators, making it concise and easy to understand.
