College Board Summary

College Board focus is on primitive types of int, double, and boolean. In unit1, String is mentioned, but it is technically a Wrapper Class. The primitive type that is building block for a String is a single character called char. String is an array of char's and the uppercase S in String means it is a Class.

Data Types

Now is a good time to understand data types. There are primitive types in Java, but you should know there are Wrapper Classes. Java likes everything to be a class. String is a Non-Primitive data type that is a Class in Java.

public class DefinePrimitives {
    public static void main(String[] args) {
      int anInt = 100;
      double aDouble = 89.9;
      boolean aBoolean = true;

      // not primitives but essential
      String aString = "Hello, World!";   // wrapper class shortcut assignment
      String aStringFormal = new String("Greetings, World!");
  
      System.out.println("anInt: " + anInt);
      System.out.println("aDouble: " + aDouble);
      System.out.println("aBoolean: " + aBoolean);
      System.out.println("aString: " + aString);
      System.out.println("aStringFormal: " + aStringFormal);
    }
  }
  DefinePrimitives.main(null)

Input Primitive data

Input is a key concept to all programming. The assignments in previous example are "static" or "hard coded". The examples when you use input are supplied by the user.

Scanner is the java utility class for console input.

// java style to import library
import java.util.Scanner;

// class must alway have 1st letter as uppercase, CamelCase is Java Class convention
public class ScanPrimitives {
    public static void main(String[] args) {    
        Scanner input;

        // primitive int
        input = new Scanner(System.in);
        System.out.print("Enter an integer: ");
        try {
            int sampleInputInt = input.nextInt();
            System.out.println(sampleInputInt);
        } catch (Exception e) {  // if not an integer
            System.out.println("Not an integer (form like 159), " + e);
        }
        input.close();

        // primitive double
        input = new Scanner(System.in);
        System.out.print("Enter a double: ");
        try {
            double sampleInputDouble = input.nextDouble();
            System.out.println(sampleInputDouble);
        } catch (Exception e) {  // if not a number
            System.out.println("Not an double (form like 9.99), " + e);
        }
        input.close();

        // primitive boolean
        input =  new Scanner(System.in);
        System.out.print("Enter a boolean: ");
        try {
            boolean sampleInputBoolean = input.nextBoolean();
            System.out.println(sampleInputBoolean);
        } catch (Exception e) {  // if not true or false
            System.out.println("Not an boolean (true or false), " + e);
        }
        input.close();

        // wrapper class String
        input =  new Scanner(System.in);
        System.out.print("Enter a String: ");
        try {
            String sampleInputString = input.nextLine();
            System.out.println(sampleInputString);
        } catch (Exception e) { // this may never happen
            System.out.println("Not an String, " + e);
        }
        input.close();
    }
}
ScanPrimitives.main(null);

Output Primitive Data

The second key to to all programming is Output. All programming has means to format and combine data. In these examples you see descriptions of the mathematical operation combine with the result of the operation.

public class PrimitiveDivision {
    public static void main(String[] args) {
        int i1 = 7, i2 = 2;
        System.out.println("Integer Division");
        System.out.println("\tint output with concatenation: " + i1 + "/" + i2 + " = " + i1/i2);
        System.out.println(String.format("\tint output with format: %d/%d = %d",i1, i2, i1/i2));
        System.out.printf("\tint output with printf: %d/%d = %d\n",i1, i2, i1/i2);

        double d1 = 7, d2 = 2;
        System.out.println("Double Division");
        System.out.println("\tdouble output with concatenation: " + d1 + "/" + d2 + " = " + d1/d2);
        System.out.println(String.format("\tdouble output with format: %.2f/%.2f = %.2f",d1, d2, d1/d2));
        System.out.printf("\tdouble output with printf: %.2f/%.2f = %.2f\n",d1, d2, d1/d2);

        System.out.println("Casting and Remainders");
        System.out.printf("\tint cast to double on division: %d/%d = %.2f\n",i1, i2, i1/(double)i2);
        System.out.println("\tint using modulo for remainder: " + i1 + "/" + i2 + " = " + i1/i2 + " remainder " + i1%i2);
    }
}
PrimitiveDivision.main(null);

Grade Calculator, putting Input and Output together

Primitive types rarely stand alone. This lab uses the primitive type double, but it also introduces the wrapper class Double. Also included is one of the most common Data Structures in Java, the ArrayList. These items are put together to create a grade calculator.

public class GradeCalculator {
    // introduction to Double wrapper class (object)
    ArrayList<Double> grades;   // similar to Python list

    // constructor, initializes ArrayList and call enterGrades method
    public GradeCalculator() {
        this.grades = new ArrayList<>();
        this.enterGrades();
    }

    // double requires test for zero versus threshold, DO NOT compare to Zero
    private boolean isZero(double value){
        double threshold = 0.001;
        return value >= -threshold && value <= threshold;
    }


    // enterGrades input method using scanner
    private void enterGrades() {
        Scanner input;

        while (true) {
            input = new Scanner(System.in);
            System.out.print("Enter a double, 0 to exit: ");
            try {
                double sampleInputDouble = input.nextDouble();
                System.out.println(sampleInputDouble);
                if (isZero(sampleInputDouble)) break;       // exit loop on isZero
                else this.grades.add(sampleInputDouble);    // adding to object, ArrayList grades
            } catch (Exception e) {  // if not a number
                System.out.println("Not an double (form like 9.99), " + e);
            }
            input.close();
        }
    }

    // average calculation 
    public double average() {
        double total = 0;   // running total
        for (double num : this.grades) {    // enhanced for loop
            total += num;   // shortcut add and assign operator
        }
        return (total / this.grades.size());  // double math, ArrayList grades object maintains its size
    }

    // static main method, used as driver and tester
    public static void main(String[] args) {
        GradeCalculator grades = new GradeCalculator(); // calls constructor, creates object, which calls enterGrades
        System.out.println("Average: " + String.format("%.2f", grades.average()));  // format used to standardize to two decimal points
    }
}
// IJava activation
GradeCalculator.main(null);

Hacks

Build your own Jupyter Notebook meeting these College Board and CTE competencies

Define in a Class the following data types
- Demonstrate use of Primitives: int, double, boolean, string
- Demonstrate use of Wrapper Class object: String
Describe in comments how each data type choice is appropriate to application
Perform arithmetic expressions and assignment in a program code Code.org Lesson
Determine what is result is in a variable as a result of an data type and expression (ie integer vs double)
Perform an arithmetic expressions that uses casting, add comments that show how it produces desired result. Learn more by watching this College Board video
Perform compound assignment operator (ie +=), add comments to describe the result of operator

Additional requirements

Multiple inputs and outputs are required
Jupyter NoteBook when committed to Fastpages must display Outputs
Building something that helps you study for another class is encouraged, here are some ideas: MPG, GPA, Celsius <--> Fahrenheit, The nth Fibonacci, GCD, Primes in range of numbers, Points per Game