Map techniques. : Map « Collections « Java Tutorial

1. Java Tutorial
2. Collections
3. Map

import java.util.Collection;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;

public class Main {
  public static void main(String args[]) {
    Map<String, Integer> atomNums = new TreeMap<String, Integer>();

    atomNums.put("A", 1);
    atomNums.put("B", 2);
    atomNums.put("C", 3);
    atomNums.put("D", 4);
    atomNums.put("E", 5);
    atomNums.put("F", 6);

    System.out.println("The map contains these " + atomNums.size() + " entries:");

    Set<Map.Entry<String, Integer>> set = atomNums.entrySet();

    for (Map.Entry<String, Integer> me : set) {
      System.out.print(me.getKey() + ", Atomic Number: ");
      System.out.println(me.getValue());
    }
    TreeMap<String, Integer> atomNums2 = new TreeMap<String, Integer>();

    atomNums2.put("Q", 30);
    atomNums2.put("W", 82);

    atomNums.putAll(atomNums2);

    set = atomNums.entrySet();

    System.out.println("The map now contains these " + atomNums.size() + " entries:");
    for (Map.Entry<String, Integer> me : set) {
      System.out.print(me.getKey() + ", Atomic Number: ");
      System.out.println(me.getValue());
    }

    if (atomNums.containsKey("A"))
      System.out.println("A has an atomic number of " + atomNums.get("A"));

    if (atomNums.containsValue(82))
      System.out.println("The atomic number 82 is in the map.");
    System.out.println();

    if (atomNums.remove("A") != null)
      System.out.println("A has been removed.\n");
    else
      System.out.println("Entry not found.\n");

    Set<String> keys = atomNums.keySet();
    for (String str : keys)
      System.out.println(str + " ");

    Collection<Integer> vals = atomNums.values();
    for (Integer n : vals)
      System.out.println(n + " ");

    atomNums.clear();
    if (atomNums.isEmpty())
      System.out.println("The map is now empty.");
  }
}