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CollectionAPI.java

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import java.util.*;

/*

This class dives into Collection API concepts, their methods, and some function Interfaces

Lists - Sets - Tree sets - Maps - Hash Maps

Add(), Get(), Sort(), indexOf(), Put(), hasNext(), next()

Comparator with compare method

*/

public class CollectionAPI {

public static void main(String [] a) {

// A list is An ordered collection, where the user has precise control

// over where in the list each element is inserted

List<Integer> list = new ArrayList<Integer>();

// Add is a method that appends the specified element to the * end * of this list

list.add(81);

list.add(54);

list.add(66);

list.add(82);

// Sorts the list into ascending order

Collections.sort(list);

// Comparator is an interface that allows us to change the logic of sorting.

// Here we are instantiating an object of Comparator and overriding the * compare * method

// that return 1 signaling an element switch of -1 signaling not to switch.

Comparator<Integer> comparator = (i, j) -> i%10 > j%10? 1 : -1;

// Here we include comparator as a parameter to sort so that we customize the sorting logic

list.sort(comparator);

// A list has get and indexOf methods

/*

Set is a collection that contains no duplicate elements.

Set does not have get and indexOf methods.

*/

Set<Integer> set = new HashSet<Integer>();

set.add(21);

set.add(5);

set.add(6);

set.add(8);

// We also have TreeSet that is similar to HashSet but sorted

TreeSet<Integer> treeSet = new TreeSet<Integer>();

treeSet.add(44);

treeSet.add(32);

treeSet.add(87);

treeSet.add(1);

// Since sets don't have get methods we use an iterator

// We can also use hasNext() and next() we get a tree set elements

for (Integer integer : treeSet) System.out.println(integer); // next fetches the next value

/*

Map is not a part of collections framework but is a part of collection api concepts

Similar to set we don't have duplicates

*/

Map<String, Integer> studentGrades = new HashMap<>();

studentGrades.put("Raed", 93);

studentGrades.put("Dani", 99);

System.out.println(studentGrades);

System.out.println(studentGrades.get("Raed"));

System.out.println(studentGrades.keySet()); // returns all keys

// Goes through the key set and fetches the value of each key

for(String key : studentGrades.keySet())

System.out.println(key + " " + studentGrades.get(key));

}

}