Develop a Java program to calculate the BMI of ‘n’ number of peopleusing constructors, methods and provide its sample output.

Sure, here is a simple Java program that calculates the BMI of 'n' number of people using constructors and methods:

import java.util.Scanner;

class Person {
    double weight;
    double height;

    // Constructor
    Person(double weight, double height) {
        this.weight = weight;
        this.height = height;
    }

    // Method to calculate BMI
    double calculateBMI() {
        return weight / (height * height);
    }
}

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter the number of people: ");
        int n = scanner.nextInt();

        Person[] people = new Person[n];

        for (int i = 0; i < n; i++) {
            System.out.println("Enter weight for person " + (i+1) + ": ");
            double weight = scanner.nextDouble();
            System.out.println("Enter height for person " + (i+1) + ": ");
            double height = scanner.nextDouble();
            people[i] = new Person(weight, height);
        }

        for (int i = 0; i < n; i++) {
            System.out.println("BMI of person " + (i+1) + " is: " + people[i].calculateBMI());
        }
    }
}

Sample Output:

Enter the number of people: 
2
Enter weight for person 1: 
70
Enter height for person 1: 
1.75
Enter weight for person 2: 
60
Enter height for person 2: 
1.65
BMI of person 1 is: 22.857142857142858
BMI of person 2 is: 22.03856749311295

This program first asks for the number of people, then for each person it asks for their weight and height. It then calculates and prints the BMI for each person.