CODEWITHSUNDEEP
javahashmap
Hitesh Misro
Hitesh Misro

Reputation: 3461

Can I swap HashMap keys and values to other?

I'm new to Java and what I want to do is to swap all the keys and values of HashMap (hm) to HashMap (hm2) and vice versa. I didn't find any solution for this. Is it possible?

import java.util.*;

class HashMapSwap{
public static void main(String args[]){
    HashMap<Integer, String> hm = new HashMap<Integer, String>();
    HashMap<Integer, String> hm2 = new HashMap<Integer, String>();
    
    hm.put(3, "Mobile");
    hm.put(11, "Tab");
    
    hm2.put(4, "PC");
    hm2.put(1, "Laptop");
    
    Map tmp = new HashMap(hm);
    tmp.keySet().removeAll(hm2.keySet());
    hm2.putAll(tmp);

    for(Map.Entry en:hm2.entrySet()){
        System.out.println(en.getKey() + " " + en.getValue());
    }
}
}

O/P :

1 Laptop

3 Mobile

4 PC

11 Tab

Upvotes: 2

Views: 1748

Answers (2)

TMichelsen
TMichelsen

Reputation: 337

// store first map in (new) temporary map
HashMap<Integer, String> tempMap = new HashMap<Integer, String>(hm);

// clear first map and store pairs of hm2
hm.clear();
hm.putAll(hm2);

// clear second map and store pairs of tempMap
hm2.clear();
hm2.putAll(tempMap);

// EDIT (hint from Palcente)
// optional: null the tempMap afterwards
tempMap = null;

Upvotes: 3

Jeet
Jeet

Reputation: 248

tmp can be used to swap references as below. 

        HashMap<Integer, String> hm = new HashMap<Integer, String>();
        HashMap<Integer, String> hm2 = new HashMap<Integer, String>();

        hm.put(3, "Mobile");
        hm.put(11, "Tab");

        hm2.put(4, "PC");
        hm2.put(1, "Laptop");

        HashMap tmp = new HashMap();
        tmp = hm;
        hm = hm2;
        hm2 = tmp;

        for(Map.Entry en:hm.entrySet()){
            System.out.println(en.getKey() + " " + en.getValue());
        }
        for(Map.Entry en:hm2.entrySet()){
            System.out.println(en.getKey() + " " + en.getValue());
        }

Upvotes: 2

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