CODEWITHSUNDEEP
java
kalpesh
kalpesh

Reputation: 189

How to sort Map in Java

i want to sort map according to its key value plz see code below

public static void main(String[] args) {

    SortedMap map = new TreeMap();

    // Add some elements:
    map.put("2", "Two");
    map.put("1", "One");
    map.put("5", "Five");
    map.put("4", "Four");
    map.put("3", "Three");
    map.put("10", "Ten");
    map.put("12", "Twelve");
    map.put("7", "Seven");
    map.put("9", "Nine");

    Iterator iterator = map.keySet().iterator();
    while (iterator.hasNext()) {
        Object key = iterator.next();
        System.out.println("key : " + key + " value :" + map.get(key));
    }


}

 Result Should come below

key : 1 value :One
key : 2 value :Two
key : 3 value :Three
key : 4 value :Four
key : 5 value :Five
key : 7 value :Seven
key : 9 value :Nine
key : 10 value :Ten
key : 12 value :Twelve

Upvotes: 2

Views: 3397

Answers (3)

polygenelubricants
polygenelubricants

Reputation: 383676

A TreeMap is a SortedMap, which sorts by keys. The way you were using it, you have String keys, and its natural ordering is lexicographical, where "11" < "2".

Here's an illustration using List to simplify:

List<String> list = new ArrayList<String>(
    Arrays.asList("2", "1", "11", "b", "a", "aa")
);
Collections.sort(list);
System.out.println(list); // prints "[1, 11, 2, a, aa, b]"

Note the analogy between 1, 11, 2 and a, aa, b. This is precisely what lexicographical ordering mandates. In a dictionary, you expect aa to appear before b. Similary, in this ordering, you expect 11 to appear before 2.

See also

If you need to compare them as Integer, use a custom Comparator<String>:

Comparator<String> stringAsInteger = new Comparator<String>() {
    @Override public int compare(String s1, String s2) {
        return Integer.valueOf(s1).compareTo(Integer.valueOf(s2));
    }
};
List<String> list = new ArrayList<String>(
    Arrays.asList("2", "1", "10", "007")
);
Collections.sort(list, stringAsInteger);
System.out.println(list); // prints "[1, 2, 007, 10]"

SortedMap<String, String> map = new TreeMap<String, String>(stringAsInteger);
map.put("2", "Two");
map.put("1", "One");
map.put("10", "Ten");
map.put("12", "Twelve");
map.put("7", "Seven");
System.out.println(map); // prints "{1=One, 2=Two, 7=Seven, 10=Ten, 12=Twelve}"

API links

Related questions

On Comparator and Comparable

On sorting Map by values

On raw types

Effective Java 2nd Edition, Item 23: Don't use raw types in new code

Related questions

Upvotes: 4

P&#233;ter T&#246;r&#246;k
P&#233;ter T&#246;r&#246;k

Reputation: 116246

I guess your problem is that keys "10" and "12" come before "2" (btw you should be more specific about your problem next time). This is simply due to the way strings are sorted.

If you want the keys to be sorted according to their integer values, you have the following options:

  • use Integer keys instead of Strings
  • insert leading zeroes into the string keys to make them equally long, i.e. "01" instead of "1" etc.
  • use a special Comparator which sorts according to your wish.

Upvotes: 10

Andreas Dolk
Andreas Dolk

Reputation: 114757

Implement a custom Comparator and create the TreeMap with this little helper. The Comparator provides the order ("1" < "2" < "3" < ... < "10" < ... < "100").

Upvotes: 4

Related Questions