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How to print collections in the Collections Framework on the console in Java ?.


Program to demonstrate how to print collections in the Collections Framework on the console in Java

package com.hubberspot.example;

// 1. Importing all the highly used Collection 
// classes, Collection and Map interface 
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.LinkedList;
import java.util.Map;
import java.util.TreeMap;
import java.util.TreeSet;

public class PrintingCollections {

 public static void main(String[] args) {

  // 2. Creating an Object of each Collection
  // --- Array ---
  int[] integers = new int[6];

  // --- Array ---
  Collection arrayList = new ArrayList();
  // --- Array ---
  Collection linkedList = new LinkedList();
  // --- Array ---
  Collection hashSet = new HashSet();
  // --- Array ---
  Collection treeSet = new TreeSet();
  // --- Array ---
  Collection linkedHashSet = new LinkedHashSet();

  // --- Array ---
  Map hashMap = new HashMap();
  // --- Array ---
  Map treeMap = new TreeMap();
  // --- Array ---
  Map linkedHashMap = new LinkedHashMap();

  // 3. Adding few elements to described Collections above
  addElements(integers);

  addElements(arrayList);
  addElements(linkedList);
  addElements(hashSet);
  addElements(treeSet);
  addElements(linkedHashSet);

  addElements(hashMap);
  addElements(treeMap);
  addElements(linkedHashMap);

  // 4. Printing all the elements in Collections

  System.out.println("The Collection printing goes like this : \n");

  // 5. Arrays are usually printed by passing whole array to 
  // Arrays class method named as toString()
  System.out.println("Array : "+Arrays.toString(integers));

  // arraylist and linkedlist usually displays elements
  // in order of their entry to Collection
  System.out.println("ArrayList : "+arrayList);
  System.out.println("LinkedList : "+linkedList);

  // hashset doesn't allow duplicate entries to be 
  // inserted in to an collection
  System.out.println("HashSet : "+hashSet);

  // treeset doesn't allow duplicate entries plus it 
  // sorts the elements added to it 
  System.out.println("TreeSet : "+treeSet);

  // linkedhashset doesn't sort the elements but it 
  // displays the order in which the elements were added
  System.out.println("LinkedHashSet : "+linkedHashSet);

  System.out.println("HashMap : "+hashMap);

  // treemap sorts the elements added to it 

  System.out.println("TreeMap : "+treeMap);

  // linkedhashmap doesn't sort the elements but it 
  // displays the order in which the elements were added
  System.out.println("LinkedHashMap : "+linkedHashMap);


 }

 // 6. For adding elements to Collection type created above
 static Collection addElements(Collection collection) {

  collection.add(3);
  collection.add(2);
  collection.add(1);
  collection.add(1);
  collection.add(2);
  collection.add(3);
  return collection;
 }

 //7. For adding elements to Map type created above
 static Map addElements(Map map) {

  map.put(6, "One");
  map.put(5, "Two");
  map.put(4, "Three");
  map.put(3, "Four");
  map.put(2, "Five");
  map.put(1, "Six");
  return map;
 }

 // 8. For adding elements to array type created above
 static int[] addElements(int[] integers) {
  integers[0] = 1;
  integers[1] = 2;
  integers[2] = 3;
  integers[3] = 4;
  integers[4] = 5;
  integers[5] = 6;
  return integers;
 }

}



Output of the program :



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