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This article focuses on "what are the simple sorting methods for Java HashMap". Interested friends may wish to take a look. The method introduced in this paper is simple, fast and practical. Let's let the editor take you to learn "what are the simple sorting methods of Java HashMap?"

HashMap is stored in no order, but is implemented according to key's HashCode.

Key= mobile phone brand, value= price, here is an example to sort by name and by price.

Map phone=new HashMap (); phone.put ("Apple", 8899); phone.put ("SAMSUNG", 7000); phone.put ("Meizu", 2698); phone.put ("Xiaomi", 1800); System.out.println (phone)

Output HashMap directly to get an unordered Map (not sequential storage like Arraylist).

1. Sort by key

To sort the names, you first need to get the keySet of the keys in HashMap and convert them to an array, so that you can sort them with Arrays.sort ().

Set set=phone.keySet (); Object [] arr=set.toArray (); Arrays.sort (arr); for (Object key:arr) {System.out.println (key);}

Get the sorted key value

Finally, the corresponding value of the key can be obtained by using HashMap.get (key).

For (Object key:arr) {System.out.println (key+ ":" + phone.get (key));}

The resulting printed result

two。 Sort by value

To sort the prices, you first need to get the view (entrySet) containing the mapping relationship in the HashMap, as shown in the figure:

Convert entrySet to List, and then rewrite the comparator comparison. Either List.sort (comparator) or Collections.sort (list,comparator) can be used here

Convert to list

List list = new ArrayList (phone.entrySet ()); / / convert to list

Sort using list.sort ()

List.sort (new Comparator () {@ Override public int compare (Map.Entry o1, Map.Entry O2) {return o2.getValue () .compareTo (o1.getValue ());}})

Sort using Collections.sort ()

Collections.sort (list, new Comparator () {@ Override public int compare (Map.Entry o1, Map.Entry O2) {return o2.getValue () .compareTo (o1.getValue ());}})

Two ways of result output

/ / for loop for (int I = 0; I < list.size (); iTunes +) {System.out.println (list.get (I). GetKey () + ":" + list.get (I). GetValue ());} / / for-each loop for (Map.Entry mapping: list) {System.out.println (mapping.getKey () + ":" + mapping.getValue ());}

Ergodic printout

/ / for for (int I = 0; I < list.size (); iTunes +) {System.out.println (list.get (I). GetKey () + ":" + list.get (I). GetValue ());} System.out.println (); / / for-each for (Map.Entry mapping: list) {System.out.println (mapping.getKey () + ":" + mapping.getValue ());}

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