Creating a Hash Table : Map « Collections Data Structure « Java

Creating a Hash Table


import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.TreeMap;

public class Main {
  public static void main(String[] argv) throws Exception {
    Map<String, Integer> map = new HashMap<String, Integer>();
    map = new TreeMap();

    map.put("a", new Integer(1));
    map.put("b", new Integer(2));
    map.put("c", new Integer(3));

    int size = map.size(); // 2

    Object oldValue = map.put("a", new Integer(9)); // 1

    oldValue = map.remove("c"); // 3

    Iterator it = map.keySet().iterator();
    while (it.hasNext()) {
      Object key =;

    it = map.values().iterator();
    while (it.hasNext()) {
      Object value =;


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