basic data structures usage examples in java

DataStructures.java

import java.util.*;

public class HelloWorld{

     public static void main(String []args){
         // Arrays 0
         System.out.println("==============");
         int[] a0 = new int[100];
         for(int i = 100; i > 0; i--) {
             a0[100 - i] = 101 * (i << 1);
         }
         Arrays.sort(a0);
         for(int i = 0; i < a0.length; i++) {
             System.out.println(a0[i]);
         }
         // PQ 1
         System.out.println("==============");
         PriorityQueue<String> q = new PriorityQueue(10, new Comparator<String>() {
             public int compare(String s1, String s2) {
                 return s2.compareTo(s1);
             }
         });
         q.add("123");
         q.add("321");
         Iterator<String> iter = q.iterator();
         while(iter.hasNext()) {
             System.out.println(iter.next());
         }
         for(String s: q) {
             System.out.println(s);
         }
         
         // Map/HashMap 2
         System.out.println("==============");
         Map<String, Integer> m2 = new HashMap<>();
         m2.put("123", 123);
         m2.put("124", 124);
         Iterator<Map.Entry<String,Integer>> i2 = m2.entrySet().iterator();
         while(i2.hasNext()) {
             Map.Entry<String, Integer> e2 = i2.next();
             System.out.println(e2.getKey());
             System.out.println(e2.getValue());
         }
         // Bits 3
         System.out.println("==============");
         int i3 = 100;
         System.out.println(i3 >> 2);
         System.out.println(i3 >>> 2);
         int ii3 = -100;
         System.out.println(ii3 >> 2);
         System.out.println(ii3 >>> 2);
         
         // Math 4
         System.out.println("==============");
         System.out.println(java.lang.Math.pow(2, 4));
         System.out.println(java.lang.Math.log(2));
         System.out.println(java.lang.Math.abs(-2));
         
         // TreeSet 5
         System.out.println("==============");
         TreeSet<String> tm5 = new TreeSet(new Comparator<String>(){
             public int compare(String s1, String s2) {
                 return s2.compareTo(s1);
             };
         });
         tm5.add("123");
         tm5.add("124");
         tm5.add("125");
         tm5.add("135");
         for(String a: tm5) {
             System.out.println(a);
         }
         System.out.println(tm5.ceiling("126")); // 125, ceilingKey, headMap
         System.out.println(tm5.floor("126")); // 135, floorKey, tailMap
         // reverse: descendingMap
         
         // LinkedList 6
         System.out.println("==============");
         LinkedList<String> ll = new LinkedList<>();
         ll.addFirst("123");
         ll.addLast("321");
         for(String a: ll) {
             System.out.println(a);
         }
         
     }
}