How to Create a Java Map That Retains Insertion Order Without Hashes?

What Java class can I use to implement a Map while keeping the order of insertion without relying on hashes?

In Java, if you want to maintain the insertion order of key-value pairs without relying on hash tables like Hashtable or HashMap, you can utilize the LinkedHashMap class. This data structure preserves the order in which keys are inserted, enabling you to retrieve elements in their respective order.

import java.util.LinkedHashMap; 
import java.util.Map;  

public class InsertionOrderMapExample {
    public static void main(String[] args) {
        // Create a LinkedHashMap to maintain insertion order
        Map<String, Module> modules = new LinkedHashMap<>(); 
        
        // Adding elements to the LinkedHashMap
        modules.put("key1", new Module("Module 1"));
        modules.put("key2", new Module("Module 2"));
        modules.put("key3", new Module("Module 3")); 
        
        // Iterating through the LinkedHashMap while preserving order
        for (Map.Entry<String, Module> entry : modules.entrySet()) { 
            String key = entry.getKey(); 
            Module module = entry.getValue(); 
            // Add module to your JPanel or perform your operations
            System.out.println(key + " : " + module.getName()); 
        } 
    } 
}

class Module {
    private String name;
    
    public Module(String name) {
        this.name = name;
    }
    
    public String getName() {
        return name;
    }
}

Solutions

• Use Java's LinkedHashMap class for key-value associations that maintain insertion order.
• Instantiate a LinkedHashMap, add your Module objects with their associated keys, and then iterate over its entry set to display them in the order they were added.

Mistake: Using HashMap instead of LinkedHashMap, leading to unordered retrieval.

Solution: Always use LinkedHashMap when you need to maintain the insertion order.

Mistake: Not utilizing the appropriate method for iteration resulting in unexpected orders.

Solution: Iterate using the entrySet() method of LinkedHashMap to ensure proper order.