Java Primitives Notebook

• Standard Deviation Calculator

Define in a Class the following data types Demonstrate use of Primitives: int, double, boolean, string Demonstrate use of Wrapper Class object: String

public class Primitives{
    int anInt = 50;
    double aDouble = 5.5;
    boolean aBoolean = true;
    String aString = "I love to code code code";
}

System.out.println(anInt);
System.out.println(aDouble);
System.out.println(aBoolean);
System.out.println(aString);

Standard Deviation Calculator

This program asks for a list of numbers. When you are finished, input 0. It will then report Standard Deviation of this set of numbers.

Note: This program was created to assist with an AP Biology Assignment where we had to calculate the Standard Deviation of a dataset.

public class STDevCalculator {
    ArrayList<Double> values;   //defines where values will go into


    public STDevCalculator() {
        this.values = new ArrayList<>();    
        this.enterValues();
    }

    
    private boolean isZero(double value){
        double threshold = 0.001;
        return value >= -threshold && value <= threshold;   //tests if the input is 0
    }


    private void enterValues() {
        Scanner input;

        while (true) {
            input = new Scanner(System.in);
            System.out.print("Enter a Value, 0 to exit: ");
            try {
                double sampleInputDouble = input.nextDouble();  //asks for a double to inputted 
                System.out.println(sampleInputDouble);
                if (isZero(sampleInputDouble)) break;       
                else this.values.add(sampleInputDouble);   
            } catch (Exception e) {  
                System.out.println("Not an double (form like 9.99), " + e); //has to be in double form
            }
            input.close();
        }
    }


    public double stdev() {
        double total = 0;  
        double m = 0;
        double s = 0;
        double sum = 0;
        for (double num : this.values) {    //Loops through and finds the sum of all of the values in the values array
            total += num; 
        }
        m = total / values.size();

        for (double num : this.values){
            sum += Math.pow((m - num), 2); //Sums up all of the values necessary in the standard deviation equation
        }
        s = Math.pow((sum / (this.values.size() - 1)), 0.5);    //Calculates the standard deviation
        return (s);
    }


    public static void main(String[] args) {
        STDevCalculator values = new STDevCalculator(); 
        System.out.println("Standard Deviation of dataset: " + String.format("%.2f", values.stdev()));
    }   
}
STDevCalculator.main(null);

Enter a Value, 0 to exit: 5.0
Enter a Value, 0 to exit: 10.0
Enter a Value, 0 to exit: 15.0
Enter a Value, 0 to exit: 20.0
Enter a Value, 0 to exit: 0.0
Standard Deviation of dataset: 6.45

Standard Deviation is the amount of variation in a dataset and is very vital in many situations regarding data analysis, making this program quite useful.