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..

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


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:  }