• all non zero numbers are true
  • the most common example: 1 = true; 0 = false
  • == checks for comparison
  • not to be confused with = which is assignment
  • != checks for inequality
  • <, >, >=, <=
  • these operands do their normal functions
  • || relates to the or function
  • && related to and function

New Vocab

Compound Boolean Expression

  • Logical operators allow you to combine and connect booleans in useful ways.
    • not, or, and
  • ! operator takes precedence over &&, and && takes precedence over || Ex: a && b || b

Truth Tables Or operator true true true true false true false true true false false false And operator true true true true false false false true false false false false Not operator true false false true

DeMorgans Law

  • easy reminder-- De Morgan’s Laws: move the NOT inside, AND becomes OR and move the NOT inside, OR becomes AND Ex: !(c == d) is equivalent to (c != d)

!(c != d) is equivalent to (c == d)

!(c < d) is equivalent to (c >= d)

!(c > d) is equivalent to (c <= d)

!(c <= d) is equivalent to (c > d)

!(c >= d) is equivalent to (c < d)

Comparing Strings, Objets, Numbers

  • comparing the objects with == returns true
  • You can also do this comparison with != to check if two objects are not aliases
  • .equals(). This method is called from a variable and it passes a parameter to compare to in order to determine if the values are equal strings Ex: 
         if(favoritMovie.equals("Gentlemen"))
 {
     System.out.println("Good Choice");
 }
 else 
 {
     System.out.println("Are you sure that's your favorite movie?");
 }
    objets Ex: Rectangle one = new Rectangle(3,7); Rectangle two = one;

boolean same = one == two; // Will be true numbers Ex: if(one.equals(two)) { System.out.println(one + " is equal to " + two); }

compound boolean tangible 

int temp = 90;
boolean sunny = true; 
if (temp > 70 && sunny) {
    System.out.println("Time to get outside!");
}

Time to get outside!

Demorgans law tangible 

boolean a = true;
boolean b = false;
if (a) {
    System.out.println("True code block");
}

if (a && !b) {
    System.out.println("True code block");
}

if (a || b) {
    System.out.println("True or False code block");
}

if ((a && !b) && (a || a)) {
    System.out.println("true or false");
}

if (!a && b ) {
    System.out.println("False code block");
}

True code block
True code block
True or False code block
true or false

comparing 

int x = 0;
int y= 1;

System.out.println(x == y);

false

Homework

2009 FRQ 3B 

public int getChargeStartTime(int chargeTime)  // determines start time to charge battery at lowest cost 
{
 int startTime = 0;
 for (int i = 1; i < 24; i++)  // iterate through the differeant start times with a returned values <= 23
 {
 if (this.getChargingCost(i, chargeTime)
 < this.getChargingCost(startTime, chargeTime))
 {
 startTime = i;
 }
 }
 return startTime;
}

2017 FRQ 1B 

public boolean isStrictlyIncreasing(){
    for(int i = 1; i < digitList.size(); i++){  // iterate through the digits 
        if (digitList.get(i-1).compareTo(digitList.get(i)) >= 0)
        {
            return false;
        }
        else
        {
            return true;
        }
    }
}

2019 FRQ 3B 

public boolean isBalanced(ArrayList<String> delimiters) {
    int open = 0;
    int close = 0;
    for (String d: delimiters) {
        if (d.equals(openDel)) {
            open++;
        } else if (d.equals(closeDel)) {
            close++;
        }

        if (close > open) return false; 
    }
    return open == close; 
}