[JAVA] HashMap and HashSet classes

HashMap class

HashMap is a collection that can manage a collection of elements that are a set of keys and values.

The following is output as a set of element name and atomic number.

import java.util.HashMap; //import

public class Sample {
  public static void main(String[] args){
    //The key is a string and the value is an integer
    HashMap<String, Integer> map = new HashMap<String, Integer>();
    String atom[] = {"hydrogen", "helium", "lithium", "beryllium"};
    map.put(atom[0], 1); // .put()Store data in
    map.put(atom[1], 2);
    map.put(atom[2], 3);
    map.put(atom[3], 4);
    System.out.println("---Atomic number---");
    for(String s:atom){
      System.out.println(s + "Is" + map.get(s) + "Turn"); // .get()Get the value with
    }
  }
}

---Atomic number---
Hydrogen is number one
Helium is number 2
Lithium is number 3
Beryllium is number 4

Main methods

HashSet class

HashSet is a collection that can store data without duplication.

The following stores APPLE character by character and outputs it.

  
import java.util.HashSet;

public class Sample {
  public static void main(String[] args){
    HashSet<String> hs = new HashSet<String>(); //Generated as String type
    hs.add("A"); //.add()Store data in
    hs.add("P");
    hs.add("P");
    hs.add("L");
    hs.add("E");
    for(String s:hs){ //Display all with a special for statement
        System.out.println(s);
    }
  }
}

Two Ps are stored, and since duplication has occurred, it is output only once.

P
A
E
L

Main methods