Constructors

As with C++, it is possible within the class definition to introduce a constructor to be run when defining an object. To illustrate this, let us consider the previous example and move the functionality of the set_values method, used to populate the array of data points, into a constructor:

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

    public stats() {
        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;
    }
}

As with C++, the constructor in Java is the same name as the class. An example of the use of this class is

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

with the constructor being run when the new stats() call is made.