Java Collection: TreeMap

The TreeMap is used to store <key, value> pairs. It is sorted according to the natural ordering of its keys, or by a Comparator provided at map creation time, depending on which constructor is used.

A few important facts about TreeMap are as follows:

1. It is not synchronized.
2. It does not allow null keys, but values can be null.

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Hierarchy of TreeMap class

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It inherits methods from AbstractMap and implements Serializable, Clonable, and NavigatableMap interfaces.

Source code of Item.java

package com.t4b.test; public class Item { String name; int id; double price; public Item(String name, int id, double price) { super(); this.name = name; this.id = id; this.price = price; } @Override public String toString() { return "Item [name=" + name + ", id=" + id + ", price=" + price + "]"; } }

Source code of TestMain.java

package com.t4b.test; import java.util.TreeMap; import java.util.Map; public class TestMain { public static void main(String[] args) { TreeMap<Integer, Item> map = new TreeMap<Integer, Item>(); map.put(1, new Item("Apple", 1, 150.0)); map.put(2, new Item("Grape", 2, 250.0)); map.put(3, new Item("Mango", 3, 10)); map.put(2, new Item("Pine Apple", 4, 100)); for (Map.Entry item : map.entrySet()) { System.out.println(item.getKey() + " : " + item.getValue()); } } }

Happy Exploring!