1. type safe - same type of element (object) are added to collection.
ArrayList<String> name = new ArrayList<>();
ex:- It depends on the type - passing an integer instead of a string will cause an error.
name.add("lakhan");
name.add("harshi");
name.add("thakur");
name.add("Singh");
name.add("Raj");
2. un type safe - different types of elements can be added to collection.
LinkedList list = new LinkedList();
ex:-
list.add("Study"); // string
list.add(123); // int
list.add(45.6); // float
list.add(true); //boolean
list.add(101.5567); // double
Framework:- Is a set of Classes and Interface which provide a ready-made architecture.
Collection Framework
Note:-
Collection Hierarchy
Code
package learn;
//import util package [all classes]
import java.util.*;
public class StartCode {
public static void main(String[] args) {
System.out.println("Welcome to java collection framework");
/*
* creating collection
*
* 1. type safe - same type of element (object) are added to collection.
* 2. un type safe - different types of elements can be added to collection.
*
* */
//type safe collection
System.out.println("\ntype safe collection");
ArrayList<String> name = new ArrayList<>();
name.add("lakhan");
name.add("harshi");
name.add("thakur");
name.add("Singh");
name.add("Raj");
System.out.println(name);
//Indexed collection
System.out.println(name.get(0)); // lakhan
System.out.println(name.get(2)); //thakur
//order is preserved
System.out.println(name); // ['lakhan','hashi','thakur','singh','raj']
//duplicate order are allowed
name.add("Raj");
System.out.println(name);//['lakhan','hashi','thakur','singh','raj','raj']
//check item is there or not
System.out.println("\ncheck item is there or not");
System.out.println(name.contains("lakhan"));
//check for empty
System.out.println("\ncheck for empty");
System.out.println(name.isEmpty());
//untype safe collection
System.out.println("\nuntype safe collection");
LinkedList list = new LinkedList();
list.add("Lakhan");
list.add(123);
list.add(45.6);
list.add(true);
list.add(101);
System.out.println(list);
//created the vector
Vector<String> vector = new Vector<>();
//add all collection(name is also a collection)
vector.addAll(name);
System.out.println("\nVectore;- "+vector);
System.out.println("\n\n----------------SET Example----------------------");
HashSet<Double> nms = new HashSet<>();
nms.add(14.14);
nms.add(34.12354);
nms.add(2354.235);
nms.add(99.3);
nms.add(9.0);
System.out.println(nms);//[14.14, 34.12354, 99.3, 2354.235]
//set have no method it use a collection all methods
//order is not preserved mean 99.3 not in index
System.out.println(nms); // [14.14, 34.12354, 99.3, 2354.235]
//duplicate order are not allowed
nms.add(99.3);
System.out.println(nms);//[14.14, 34.12354, 99.3, 2354.235]
TreeSet<Double> tset = new TreeSet<>();
System.out.println("\nTreeSet is sorted");
tset.addAll(nms);
System.out.println(tset);
}
}
Traverse
package learn;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.ListIterator;
import java.util.TreeSet;
public class TraverseExample {
public static void main(String[] args) {
ArrayList<String> name = new ArrayList<>();
name.add("lakhan");
name.add("harshi");
name.add("thakur");
name.add("Singh");
name.add("ABC");
//for each loop:
System.out.println("For each traverse\n");
for (String str:name)
{
System.out.print(str + "\t" + str.length()+"\t");
StringBuffer br = new StringBuffer(str);
System.out.println(br.reverse());
}
System.out.println("_____________________");
//traversing using ITERATOR : Forward traversing
Iterator<String> itr = name.iterator();
while(itr.hasNext())
{
String next = itr.next();
System.out.println(next);
}
System.out.println("_____________________");
//Backward traversal of collection LISTITERATOR
System.out.println("Backward traversal of collection LISTITERATOR");
ListIterator<String> litr = name.listIterator(name.size());
while (litr.hasPrevious()){
String previous = litr.previous();
System.out.println(previous);
}
System.out.println("_____________________");
//for each method (this is java 8 feature)
System.out.println("\nFor each method (this is java 8 feature)\n");
name.forEach(e->{
System.out.println(e);
});
System.out.println("_____________________");
//Tree set
System.out.println("____________TREE SET SORTING OF ELEMENT_________");
TreeSet<String> set = new TreeSet<>();
set.addAll(name);
set.forEach(str->{
System.out.println(str);
});
}
}
Output:-
For each traverse
lakhan 6 nahkal
harshi 6 ihsrah
thakur 6 rukaht
Singh 5 hgniS
ABC 3 CBA
_____________________
lakhan
harshi
thakur
Singh
ABC
_____________________
Backward traversal of collection LISTITERATOR
ABC
Singh
thakur
harshi
lakhan
_____________________
For each method (this is java 8 feature)
lakhan
harshi
thakur
Singh
ABC
_____________________
____________TREE SET SORTING OF ELEMENT_________
ABC
Singh
harshi
lakhan
thakur
Process finished with exit code 0
Map
- Keys are unique (no duplicates allowed).
- Each key maps to exactly one value.
- Values can be duplicates.
package learn;
import java.util.HashMap;
public class MapExample {
public static void main(String[] args) {
HashMap<String, Integer> courses = new HashMap<>();
//adding element
courses.put("Core Java", 4000);
courses.put("Basic Python", 3500);
courses.put("Spring", 8000);
courses.put("Android", 4000); //key duplicate
courses.put("Android", 6000);
courses.put("Php", 6000);
System.out.println(courses);
System.out.println("___________\n");
courses.forEach((e1,e2)->{
System.out.println(e1+ " => " +e2);
//e1 is key and e2 is value
});
courses.forEach((key,value)->{
System.out.print(key);
System.out.print("=>");
System.out.print(value);
System.out.print("\n");
});
//get index of key
System.out.println("_____Need to know the free of core java______\n");
System.out.println(courses.get("Core Java"));
}
}
output:-
{Core Java=4000, Php=6000, Basic Python=3500, Spring=8000, Android=6000}
___________
Core Java=>4000
Php=>6000
Basic Python=>3500
Spring=>8000
Android=>6000
_____Need to know the free of core java______
4000
Map vs. Set vs. List
Feature | List | Set | Map |
Duplicates allowed? | Yes | No | Keys: No Values: Yes |
Stores key-value pairs? | No | No | Yes |
Maintains order? | Yes | No (unless using TreeSet or LinkedHashSet) | No (unless using TreeMap or LinkedHashMap) |
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