How to Calculate median in Java? | With Array and List | Programming Blog

Find median of Java Array and List values using 2 ways

What is Median?

Median is mid value of particular data set. This data set must be sorted. 

In simple word, Median is mid value of sorted data.

Median will be middle, if total number of elements is odd or average of middle elements when total number of elements is even.

Example :

When total number of elements are odd

1, 2, 3, 4, 5, 6, 7
Median will be : 4

2, 3, 5, 7, 8
Median will be : 5

When total number of elements are even

1, 2, 3, 4
Median will be : (2+3) / 2 : 2.5

2, 4, 6, 8, 10, 20, 25, 30
Median will be : (8+10) / 2 : 9

So the formula become for our code :

For odd elements :

Median = (Total length / 2)

For even elements :

Median = (Total length / 2) + (Total length / 2 - 1) / 2

So lets jump on code. We will take elements form user.

Method 1 : Using code logic

In this approach, we does not use any library function for find median.

Example 1 : Find median from Java array

import java.util.Arrays;
import java.util.Scanner;

public class FindTheMedian {

    public static void main(String[] args) {
        
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter total elements length");
        int length = sc.nextInt();
        int[] array = new int[length];
        System.out.println("Enter elements");
        for (int i = 0; i < length; i++) {
            array[i] = sc.nextInt();
        }
        
        // Sort the Array
        Arrays.sort(array);
        double median = 0;
        
        // When total length is Even
        if (length % 2 == 0) {
            median = ((double) array[length/2] + (double) array[(length/2) - 1]) / 2;
        
        // When total length is Odd
        } else {
            median = (double) array[length/2];
        }
        
        System.out.println("Median is : "+median);
    }
}

Output :

Enter total elements length
6
Enter elements
2 4 6 8 10 15
Median is : 7.0

Enter total elements length
5
Enter elements
1 2 3 4 5
Median is : 3.0

Example 2 : Find median from Java List

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Scanner;

public class FindTheMedian {

    public static void main(String[] args) {
       
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter total elements length");
        int length = sc.nextInt();
       
        System.out.println("Enter elements");
        List<Integer> list = new ArrayList<>();
        for (int i = 0; i < length; i++) {
            list.add(sc.nextInt());
        }
       
        // Sort the List
        Collections.sort(list);
        double median = 0;
       
        // When total length is Even
        if (length % 2 == 0) {
            median = ((double)list.get(length/2) + (double)list.get((length/2)-1)) / 2;
        }
       
        // When total length is Odd
        else {
            median = (double)list.get(length/2);
        }

        System.out.println("Median is : "+median);
    }
}

Output :

Enter total elements length
8
Enter elements
5 1 6 8 10 0 2 7
Median is : 5.5

Enter total elements length
5
Enter elements
90 10 8 50 15
Median is : 15.0

Method 2 : Using Apache commons library

This problem can also solve by Apache commons Math library. 

org.apache.commons.math3.stat.descriptive.rank.Median package provides solution for evaluate median of array.

We must have to use double array for use this library. lets see how ii works.

import java.util.Scanner;

import org.apache.commons.math3.stat.descriptive.rank.Median;

public class FindTheMedian {

    public static void main(String[] args) {
        
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter total elements length");
        int length = sc.nextInt();
        double[] array = new double[length];
        
        System.out.println("Enter elements");
        for (int i = 0; i < length; i++) {
            array[i] = sc.nextDouble();
        }
        
        Median median = new Median();
        double answer = median.evaluate(array);
        System.out.println(answer);
    }
}

Output :

Enter total elements length
6
Enter elements
10 15 8 4 9 7
8.5

Enter total elements length
5
Enter elements
9 7 2 5 1
5.0

 

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