Create Map in Java

Create Map in Java

In Java, you can create a Map using various implementations provided by the Java Collections Framework. The most commonly used Map implementations are HashMap, TreeMap, and LinkedHashMap. Here's how you can create a Map using each of these implementations:

  1. HashMap:

    • HashMap is an unordered, key-value map that provides fast lookup and insertion. It does not guarantee any specific order of elements.
    import java.util.HashMap; import java.util.Map; public class HashMapExample { public static void main(String[] args) { Map<String, Integer> hashMap = new HashMap<>(); hashMap.put("Alice", 25); hashMap.put("Bob", 30); hashMap.put("Charlie", 22); // Access values by key int age = hashMap.get("Alice"); System.out.println("Alice's age: " + age); } }

  2. TreeMap:

    • TreeMap is a sorted map that maintains elements in ascending order based on the keys. It is backed by a Red-Black Tree data structure.
    import java.util.Map; import java.util.TreeMap; public class TreeMapExample { public static void main(String[] args) { Map<String, Integer> treeMap = new TreeMap<>(); treeMap.put("Alice", 25); treeMap.put("Bob", 30); treeMap.put("Charlie", 22); // Elements are sorted by keys for (Map.Entry<String, Integer> entry : treeMap.entrySet()) { System.out.println(entry.getKey() + ": " + entry.getValue()); } } }

  3. LinkedHashMap:

    • LinkedHashMap is an ordered map that maintains elements in the order they were inserted. It combines the features of HashMap and LinkedHashSet.
    import java.util.Map; import java.util.LinkedHashMap; public class LinkedHashMapExample { public static void main(String[] args) { Map<String, Integer> linkedHashMap = new LinkedHashMap<>(); linkedHashMap.put("Alice", 25); linkedHashMap.put("Bob", 30); linkedHashMap.put("Charlie", 22); // Elements are in insertion order for (Map.Entry<String, Integer> entry : linkedHashMap.entrySet()) { System.out.println(entry.getKey() + ": " + entry.getValue()); } } }

Choose the Map implementation that best fits your requirements based on factors like ordering, performance, and duplicate key handling. Each Map implementation has its own characteristics and use cases.

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