Thread: HashMap : Simple Usage and Understanding

Map is an object that stores key/volume pairs. Given a key, you can find its value. Keys must be unique, but values may be duplicated.

The HashMap class uses a hash table to implementation of the map interface. This allows the execution time of basic operations, such as get() and put() to be constant.


An example is below:

Q. Find the numbers Divisible by an array of numbers ie div[] between a range ie from 1 to N?
Ans. This can be solved using many ways, but we will be solving using HashMap which will help u understand the concept of HashMap in a better way..

NOTE:
For this u can use your command prompt, eclipse, netbeans or any IDE that supports JAVA. Using eclipse is much easier.


CODE :

1:  import java.util.HashMap; 
 
2:  public class Main { 
 
3:    public static int usingHashmap(int N,int div[]){ 
 
4:      int count=0; 
 
5:      HashMap<Integer, Integer> key=new HashMap<Integer, Integer>(); 
 
6:      for(int i=1;i<N;i++){ 
 
7:        key.put(i, i); 
 
8:      } 
 
9:      for(int i=0;i<div.length;i++){ 
 
10:        for(int k=1;k<N;k++){ 
 
11:        if(key.get(k)==null){ 
 
12:          key.put(k, -1); 
 
13:        } 
 
14:          if(key.get(k)%div[i]==0){ 
 
15:            count++; 
 
16:            key.remove(k); 
 
17:          } 
 
18:        } 
 
19:      } 
 
20:      System.out.println(count); 
 
21:      return count; 
 
22:    } 
 
23:    public static void main(String[] args) { 
 
24:      new Main().usingHashmap(50, new int[]{3,2}); 
 
25:    } 
 
26:  }