Java Collection: Comparable Interface

The Comparable interface (in java.lang package) is used to order the objects of user-defined class. It has compareTo(Object) method, which is used to sort objects based on a specific attribute declared in the user-defined class.

The following example shows, how this interface is used.

Source code of Item.java

package com.t4b.test; public class Item implements Comparable<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 + "]"; } @Override public int compareTo(Item o) { if (id == o.id) return 0; else if (id > o.id) return 1; else return -1; } }

Source code of TestMain.java

package com.t4b.test; import java.util.ArrayList; import java.util.Collections; import java.util.Iterator; public class TestMain { public static void main(String[] args) { ArrayList<Item> items = new ArrayList<Item>(); items.add(new Item("Apple", 1, 150.0)); items.add(new Item("Bag", 3, 1050.0)); items.add(new Item("Grape", 2, 250.0)); Collections.sort(items); Iterator<Item> itr = items.iterator(); while (itr.hasNext()) { System.out.println(itr.next()); } } }

Happy Exploring!