Map Sorting Using Comparator

This Post about sorting TreeMap.

TreeMap Actually sorts values by key. Inorder to sort Map by values we have to use comparator. The below program illustrates this.


public class ComparatorClassDemo {
 
    public static void main(String[] args) {
     
        HashMap<Integer,String> map = new HashMap<Integer,String>();
        ValueComparator bvc =  new ValueComparator(map);
        TreeMap<Integer,String> sorted_map = new TreeMap(bvc);
     
     
        map.put(1,"Arogya");
        map.put(2,"wer");
        map.put(3,"dfg");
        map.put(6,"io");
        map.put(5,"lkaldfk");
        map.put(4,"bkjaskj");
       
System.out.println("Before usage of comparator"+map);
     
     
        sorted_map.putAll(map);
     
        System.out.println("results");
        for (int key : sorted_map.keySet()) {
            System.out.println("key/value: " + key + "/"+sorted_map.get(key));
        }
    }
 
}
class ValueComparator implements Comparator {
    Map base;
  public ValueComparator(Map base) {
      this.base = base;
  }

  public int compare(Object a, Object b) {
    String name=(String)base.get(a);
    String name1=(String)base.get(b);
    return name.compareTo(name1);
  }
}



OutPut:





{2=wer, 4=bkjaskj, 6=io, 1=Arogya, 3=dfg, 5=lkaldfk}
results
key/value: 1/Arogya
key/value: 4/bkjaskj
key/value: 3/dfg
key/value: 6/io
key/value: 5/lkaldfk
key/value: 2/wer