Java Collection

basic java collection, short explain

Basic of Java Collection is a base of developer in java While it’s importent almost because It’s manage data in array and adapt to your project so easy use any data

https://www.javatpoint.com/collections-in-java

1. ArrayList class
2. LinkedList class
3. List interface
4. HashSet class
5. LinkedHashSet class
6. TreeSet class
7. PriorityQueue class
8. Map interface
9. HashMap class
10. LinkedHashMap class
11. TreeMap class
12. Hashtable class
13. Sorting
14. Comparable interface
15. Comparator interface
16. Properties class in Java

Arraylist : flixible to store data and get data so easy
LinkList: easy to add remove
HashSet Set contains unique elements only.
Sorting: sorting the elements of collection
Maps : store data by Key and Value

Array list

Array list is a Collections that keep data as normally array but the think that different is Arraylist It can reduce and enlarge automaticly follow data inside that make is flixible for working because don’t declare max size forword with normal Array

import java.util.ArrayList;

public class ArrayListExample {

    public static void main (String[] args) {
        
        ArrayList<String> names = new ArrayList<String>();
        names.add("Mateo");
        names.add("Danny");
        names.add("Joe");
        names.add("Alex");
        
        System.out.println(names.size() + " people in the list");
        
        // Access list through  it index
        System.out.println("name[0] = " + names.get(0));
        System.out.println("name[3] = " + names.get(3));
        
        // Iterate through ArrayList usign foreach
        for (String name: names) {
            System.out.print(name + " ");
        }
        System.out.println();
        
        // Iterate through ArrayList using index (reverse)
        for (int i = names.size() - 1; i >= 0; i--) {
            System.out.print(names.get(i) + " ");
        }
        System.out.println();
        
        // Check if the list contain Mateo
        if (names.contains("Mateo")) {
            System.out.println("Mateo is in the list");
        } else {
            System.out.println("Mateo is not in the list");
        }
        
        // Get Danny's index
        int dannyIndex = names.indexOf("Danny");
        System.out.println("Index of Danny is " + dannyIndex); 
        // Change Danny to Max
        names.set(dannyIndex, "Max");
        
        // Remove joe from the list
        names.remove("Joe");
        
        // Iterate through ArrayList usign foreach
        for (String name: names) {
            System.out.print(name + " ");
        }
        System.out.println();
        
        // Clear all list data
        names.clear();
        
        if(names.isEmpty()) {
            System.out.println("List is now empty");
        }

    }

}

Maps

Maps is a Coolection that have a pattern store that is Key Value

import java.util.HashMap;

public class HashMapExample {
    
    public static void main (String[] args) {
        
       HashMap<String, String> country = new HashMap<>();
       country.put("de", "German");
       country.put("th", "Thailand");
       country.put("us", "United State");
       country.put("tr", "Turkey");
       
       System.out.println("Map size = " + country.size());
       
       System.out.println("de = " + country.get("de"));
       System.out.println("th = " + country.get("th"));
       System.out.println("th = " + country.get("uk"));
       
       System.out.println("Iterate over each Entry in HashMap");
       for (HashMap.Entry<String, String> entry : country.entrySet())
       {
           System.out.println(entry.getKey() + " = " + entry.getValue());
       }
       
       country.remove("tr");
       if(country.containsKey("tr")) {
           System.out.println("Turkey exist in the map");
       } else {
           System.out.println("Turkey does not exist in the map");
       }
       
       country.clear();
       System.out.println("Map size = " + country.size());
            
    }
}

Stack

Stack is structor of data that use store data by Pattern First in last out, data will be put to stack first to it’s removed later that is only push data one way for working with Stack when we put data in to Stack it’s called Push and when bring data out from stack it’s called Pop

 import java.util.Stack;

public class StackExample {
    
    public static void main (String[] args) {
        
        Stack<String> fruit = new Stack<>();

        // Add four fruits to stack
        fruit.push("Apple");
        fruit.push("Banana");
        fruit.push("Melon");
        fruit.push("Peach");
        
        System.out.println("Pop " + fruit.pop() + " from stack");
        System.out.println("Pop " + fruit.pop() + " from stack");
        System.out.println("Pop " + fruit.pop() + " from stack");
        System.out.println("Pop " + fruit.pop() + " from stack");
        
        if (fruit.isEmpty()) {
            System.out.println("Stack is empty");
        }
        
    }
}

Collections in Java - javatpoint