How comparator works in java ?

// If you use TreeSet the data will be inserted  in natural sorting order and duplicates are not permitted

Code for inserted data in natural sorting order

package com.awf.org;

import java.util.Set;
import java.util.TreeSet;

public class IntegerAdditionExample {
public static void main (String args[]){
    Set<Integer> addSet=new TreeSet<Integer>();
    addSet.add(10);
    addSet.add(0);
    addSet.add(15);
    addSet.add(20);
    addSet.add(20);
    System.out.println("TreeSet contents ::"+addSet);
}
}

Output ::

TreeSet contents ::[0, 10, 15, 20]

In the above output you can see that the data is displayed in ascending order .
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If you want to display insertion data in Customized sorting (descending order) you can go for Comparator.

Code for inserted data in Customized sorting order using comparator

package com.awf.org;

import java.util.Comparator;
import java.util.Set;
import java.util.TreeSet;

public class IntegerAdditionExample {
public static void main (String args[]){
    Set<Integer> addSet=new TreeSet<Integer>(new MyComparator());
    addSet.add(10);
    addSet.add(0);
    addSet.add(15);
    addSet.add(20);
    addSet.add(20);
    System.out.println("TreeSet contents ::"+addSet);
}
}


class MyComparator implements Comparator<Integer>{

    @Override
    public int compare(Integer obj1, Integer obj2) {
        if(obj1<obj2){
            return 1;
        }else if (obj1>obj2){
            return -1;
        }else{
            return 0;
        }
    }
   
}

Output ::

TreeSet contents ::[20,15,10,0]

 The Input data order : [10,0,15,20,20]

In Comparator we used the below code

if(obj1<obj2){
            return 1; //Insert data in right side of the tree
        }else if (obj1>obj2){
            return -1; // Insert data in the left side of the tree
        }else{
            return 0;
        }

First Iteration :[10,0,15,20,20] 

For Tree I used Green for root ,blue for left element and pink for right element

It wont compare anything directly it will insert data 10      

Second Iteration :[10,0,15,20,20]

The data 0  (obj1) is compared with 10  (obj2)

0<10 retrun +1 . It will traverse right side from the root

 [10,0]

Third Iteration :[10,0,15,20,20]

Now Obj1=15 Obj2=10
Always it will begins with root element (already root element is 10)

1) 15 > 10 it will return -1 . so 15 will be inserted in the left side of the root

now your output is like [15,10,0]

Fourth  Iteration :[10,0,15,20,20]

obj1=20 ,obj2=10
First it will compared with root
20 >10 it will come left side, which has already element 15 so 20 is compared with 15

20 >15 so again it will come left side and inserted after 15.

 now your output is like [20,15,10,0]

Fifth  Iteration :[10,0,15,20,20]

obj1=20 ,obj2=10
First it will compared with root
20 >10 it will come left side, which has already element 15 so 20 is compared with 15


20 >15 so again left side we have element 20
20 is compared with 20
20==20 so it will return 0 means it wont insert data in tree because duplication is not allowed
 Now your output is like [20,15,10,0] 


Finally Tree traversal in inorder [left ,root,right]

so finally you will get data in descending order for the above code.

 [20,15,10,0] 

Regards,

R.Tamilanban M.E CSE

AWF community