Unit 1
Temperature Converter
- Primitives Notes
- Data Types
- Input Primitives
- Output Primitive Data
- Grade Calculator
- Primitives Hacks
-
primitive data types: lowercase
- boolean
- integers
- doubles
- float
- character
-
non primitive data types: uppercase
- wrapper class - string
- arrays
-
wrapper classes used to convert any data type into an object
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)
- hard coded: variables are assigned values beforehand
- dynamic: variable values are determined by user input
- scanner: 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);
- Examples show 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);
- Lab uses primitive double and Wrapper Class double
- Uses ArrayList
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);
import java.util.Scanner;
public class CelciustoKelvin {
public static void main (String[] args) {
Scanner input;
//we used a wrapper class to introduce our program to the user.
String aString = "This is our program to convert Celcius to Kelvin. We are using it for our AP Chemistry class.";
System.out.println(aString);
//we used the string to greet the user
input = new Scanner(System.in);
System.out.println("Enter your name as a string: ");
String name = input.nextLine();
System.out.println("Hello " + name );
input.close();
//the integer is used to get the age of the user
input = new Scanner(System.in);
System.out.println("Enter your age as an integer: ");
String age = input.nextLine();
System.out.println("You are " + age + " years old." );
input.close();
//boolean is used to get a true or false answer about whether the user is in AP Chemistry
input = new Scanner(System.in);
System.out.println("Are you in AP Chemistry? Enter your answer as a Boolean: ");
String chem = input.nextLine();
System.out.println("Your answer: " + chem);
input.close();
//double is used to get a number from the user and convert it using arithmetic expression
input = new Scanner(System.in);
System.out.println("Enter a degree in Celsius as a double: ");
double celsius = input.nextDouble();
double kelvin = (celsius + 273.0);
System.out.println( celsius + " degree Celsius is equal to " + kelvin + " in Kelvin");
input.close();
}
}
CelciustoKelvin.main(null);