Classes

As a simple illustration of working with classes in Java, let us construct a class that, for an array of integers, calculates the average. The basic class we'll call stats, and will be defined in a file stats.java:

// file stats.java
public class stats {
    int N = 200;
    public int[] values;
    public double average;

    public void set_values() {
        int j;
        values = new int[N];
        for(j=0; j<N; j++) {
            values[j] = 1 + (int) (100.0*Math.random());
        }
    }

    public void avg() {
        int sum=0, j;
        for(j=0; j<N; j++) {
            sum += values[j];
        }
        average = (double) sum / (double) N;
    }
}

where, for illustration, we use a random set of 200 integers between 0 and 100 as a data set, set within the set_values method. A program illustrating the use of this class is contained in data.java:

// file data.java
public class data {
    public static void main(String[] args) {
        stats my_data = new stats();
        my_data.set_values();
        my_data.avg();
        System.out.println("The average is " + my_data.average);
    }
}

This can be compiled and run as

  javac stats.java
  javac data.java
  java data

where, on Unix, you may have to set the environment variable CLASSPATH to the current directory in order that the stats class file be found.