Primitives Class Notes

Why Java

  • Has simple syntax
  • Allows for automatic garage collection
  • More flexible and efficient because its OO
  • It can be run on any platform
    • First compose with Java
    • Then into byte code
    • Then runs on a jvm
  • It allows for multi threading
  • Secure

    Primitives vs. Non primitives

  • Primitives
    • Predefined
    • Lowercase
    • “Primitives”
    • Cannot call methods
    • Value
    • Different sizes based on which primitive it is
  • Non primitives
    • Done by you
    • Uppercase
    • “Reference types”
    • Can call methods
    • Can be null
    • All same size Primitives Types
  • Boolean
    • One bit
  • Int
    • 2-3 bits
  • Double
    • Decimals
    • 64 bits
  • Char, float, long, etc

    Review Cont

  • Variable naming conventions
    • Letters, numbers, or underscores — nothing else
    • Typically starts with lowercase and then a capital
    • The final keyword means that the value cannot be changed later
  • Casting
    • Manual casting vs automatic
    • Widening happens automatically and you go from small data type to bigger data type
      • Ex: int to double
    • Narrowing is going from bigger data type to a smaller one and you have to declare it

Hacks

  1. 10/4 is equal to 2.5 which will round down to 2 or round up to 3 depending on the rounding since it is an integer data type. –> 2 
    int x = 10;
int y = 4; 
int z = x/y;
/// What is the value of z?


  2. val is 205 and its going to be looped 5 total times. 2 to the power of 5 is 32. 205/32 is equal to 6. –> 
    int val = 205;
for(int i=0; i<5; i++>) {
  val/=2;
}
// At the end of its executition, what is the value of the variable val in the code above?


  3. A is not a valid assignment statement because the variable is not on the left side of the assignment sign. D is not a valid assignment statement because the equation is on the left side and not the right side of the assignment sign. –? a, d

  4. I is being added to itself and the loop executes 5 times. So 3+3>6+6>12+12>24+24>48+48=96 –> 96 
    int i = 3;
for(int j=5;j>0;j--){
  i += i;
}
// What will be the value of i at the end of this loop's iteration


  5. The loop iterates 4 times. 51>52>103>304 = 120 –> 120 
    int i =5, p=27;
for(int l=23;l<p;l++>){
  i *= (l-22);
}
// What is the value for I at the end of the code above?


  6. This is an example of casting that converts the doubles into int. This is narrowing casting since the data type is getting smaller. 455 + 3.75 = 458.75 rounded up is 459 or rounded down is 458 –> 458 
    int i = 100;
double d = 4.55, d2 = 3.75;
int j = (int)(d*100 + d2);
// What is the value of j at the end of the code's execution?

FRQ 2006

1 Part A

// boolean meaning return type true or false
public boolean conflictsWith(Appointment other){
  // getting the time of two different appointments and checking if they overlap with one another using given method
  if (getTime().overlapsWith(other.getTime())){
    return true;
    // returning true if there is an overlap otherwise false is returned
  else {
    return false;
  }
}
}

1 Part B

public void clearConflicts(Appointment appt){
  // Looping through each appointment in the appointment list array list
  for (int i = 0; i < apptList.size(); i++){
    // Using given methods to check if the paramater appointment conflists with any appointments already in the appointment arraylist
    if (appt.conflictsWith(apptList(i))){
      // if the appointments overlap then the appointment at the given index will be removed from the array list
      appList.remove(i);
    }
  }
}

1 Part C

public boolean addAppt(Appointment appt, boolean emergency){
  // if there is an emergency then the appointment will clear
  if (emergency) {
    clearConflicts(appt);
    }
  else {
    // otherwise it loops through the appointment list and checks if that appointment conflicts with another appointment using the get method
    for (int i = 0; i < apptList.size(); i++) {
      if (appt.conflictsWith((Appointment)apptList.get(i))) {
        return false;
      }
    }
  }
 return apptList.add(appt);
  
}

2 Part A

public double purchasePrice(){
  return ((1 + taxrate) * getListPrice());
  
}

3 Part A

public int compareCustomer(Customer other){
 int nameCompare = getName().compareTo(other.getName());
 if (nameCompare != 0) {
  return nameCompare;
 }
 else {
  return getID() - other.getID();
 } 
}