Topics Discussed: Boolean Logic / Operators
Source Code for Lesson 9:
import java.lang.Math;
import java.util.Scanner;
class Jtutorial1 {
public static void main(String args[]){
Scanner input = new Scanner(System.in);
// Declare a double, run some tests on it.
// Is it even or odd? Is it a perfect square? Is it a whole number?
// Is the number squared even?
//<, <=, >, >=, || , &&, !=
double choice=0;
boolean isEven=false, isPS=false, isWhole=false, isSquaredEven=false;
System.out.println("Enter a value for the variable: ");
choice = input.nextDouble();
//even
if((choice%2) < 1){
isEven=true;
//System.out.println("The number " + choice + " is even prior to the decimal point. ");
}
else{
isEven=false;
//System.out.println("The number " + choice + " is NOT even. ");
}
//perfect square
if(((Math.sqrt(choice))%1) == 0){//sqrt(9) == 3
isPS=true;
//System.out.println("The number " + choice + " is a perfect square: " + Math.sqrt(choice));
}
else{
isPS=false;
//System.out.println("The number " + choice + " is NOT a perfect square: " + Math.sqrt(choice));
}
if ((choice%1) == 0){
isWhole=true;
//System.out.println("The number " + choice + " is a whole number: ");
}
else {
isWhole=false;
//System.out.println("The number " + choice + " is NOT a whole number: ");
}
if((((Math.pow(choice, 2)))%2) == 0){
isSquaredEven=true;
//System.out.println("The number " + choice + " squared is even: "+ Math.pow(choice, 2));
}
else{
isSquaredEven=false;
//System.out.println("The number " + choice + " squared is NOT even: " + Math.pow(choice, 2));
}
if(isEven){
System.out.println("The number is even. ");
}
if(isPS){
System.out.println("The number is a perfect square. ");
}
if(isWhole){
System.out.println("The number is whole. ");
}
if(isSquaredEven){
System.out.println("The number sqared is even. ");
}
} //End main
} //End class
HomeWork for Lesson 9:
/*
* See math operations in java here: https://docs.oracle.com/javase/8/docs/api/java/lang/Math.html
* Each of these operators can be called like I called Math.pow (ex: Math.abs(variable) )
*
* Problems that you should try to solve-- Pick one or more!
* A: Allow the user to enter a telephone number, use an if statement to invalidate numbers that are too long / short in length
* if the telephone number is within the right length, seperate the numbers appropriately into how they would appear in your
* country of origin: Ex. 7818789000 would turn into 781-878-9000 in the USA. (This won't require much but mod / division)
* Hint: Use long or double if you need to use a big number.
*
* B: Write a program that will allow you to input a number to select an operation (output a menu, then allow the user to select one).
* In that menu you should be allowing the user to choose a shape (circle, square, rectangle, etc). Once they select it, ask them to
* input the dimensions of it (circle can be radius, diameter, circumferece, rectangle can be length, width, perimeter or area.... etc etc.)
* Once you have taken in a few points of input, calculate the missing pieces of information. Perhaps someone has a rectangle
* where they have the area and the length, but not the width. Using java, figure out what the missing width is.
*
* C: Extra credit for people that are antsy to get some after the last 2 assignments:
* write a program that determines the last digit of 3^n power (3^3 = 27, thus 7). Hint, you can use n%4 to help you on this one.
*/
Boolean operators
Boolean operators are variables which have two states, “true” or “false” (default is false if you use a simple declaration). These can be used in a variety of ways, but are most typically seen when you need to confirm that something happened in an if statement or a loop (in later lessons). Here’s a few examples:
int empPay1=0;
boolean isChanged;//ischanged defaults to false
System.out.println("Enter the income for employee 1 that is greater than 0.");
empPay1= input.nextInt(); // Enter pay
if (empPay1 > 0){// if the value is > 0, meaning it's been changed
isChanged=true;
}
if(isChanged){//if the value has been changed (by the if above)
System.out.println("empPay has been changed");
}//You could just use an else here, but instead you could use the following:
if(!isChanged){
System.out.println("empPay has not been changed");
}
In the above example I show that booleans can be used in place of the standard if conditionals and used as a simple true / false that is set as part of another conditional. At present these must seem convoluted, but in the future when our variables change around a bit more it will make more sense to use these than other pieces of code.