HashSet, HashMap usage

10 Nov 2021 in Algorithms

HashSet

• Initialization

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

• Adding elements

  s.add(1);
  s.add(3);
  

• Remove elements

  s.remove(1);
  

• Check if the element exists

  s.contains(1);
  

• Iteration

  for(int i : s){
      System.out.println(i);
  }
  

• Empty

  s.isEmpty();
  

• Clear

  s.clear();
  

HashMap

• Initialization

  Map<Integer,Integer> m = new HashMap<>();
  

• Adding elements

  m.put(1,1);
  m.put(3,2);
  

• Delete Key

  m.remove(1);
  

• Check if the Key exists

  m.containsKey(1);
  

• Iteration

  for (Map.Entry<Integer, Integer> entry : m.entrySet()) {
          System.out.print("(" + entry.getKey() + "," + entry.getValue() + ") ");}
  

• clear the hash map

  m.clear();
  

• Check if the hash map is empty

  if (m.isEmpty()) {
          System.out.println("hash map is empty now!");
      }