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PrimesFactory Lab

PrimesFactory Lab. Laugh if you get the pun. Don’t forget: You can copy-paste this slide into other presentations, and move or resize the poll. Poll: Which of these is not a prime number?. Prime Numbers.

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PrimesFactory Lab

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  1. PrimesFactory Lab Laugh if you get the pun

  2. Don’t forget: You can copy-paste this slide into other presentations, and move or resize the poll. Poll: Which of these is not a prime number?

  3. Prime Numbers • A prime number (or a prime) is a natural number greater than 1 that has no positive divisors other than 1 and itself. • 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89… • If a number p is prime, then the only cases where p % t == 0 are when t==1 or t==p • e.g. If the number 23 is prime, then the only cases where 23 % t == 0 are when t==1 or t==23

  4. Don’t forget: You can copy-paste this slide into other presentations, and move or resize the poll. Poll: Which one of these is not a factor of 45...

  5. Factors • In mathematics, a divisor of an integer n, also called a factor of n, is an integer which divides n without leaving a remainder. • Factors of 24 • 1, 2, 3, 4, 6, 8,12, 24 • For an integer n, the factors t are numbers that satisfy the rule n % t == 0

  6. Don’t forget: You can copy-paste this slide into other presentations, and move or resize the poll. Poll: Which of these is not a prime factor of ...

  7. Prime Factors • The prime factors of a positive integer are the prime numbers that divide that integer exactly. • Factors of 24 • 1, 2, 3, 4, 6, 8,12, 24 • Prime factors of 24 are 2 and 3

  8. PrimesFactory • Three important methods • Calculate the prime factorization of any number • Print a list of all prime numbers • State whether or not a given number is a prime number

  9. PrimesFactory • Three important methods • getPrimeFactors(intnum) • //returns an ArrayList with all of the prime factors of num • listPrimesUpTo(intnum) • //returns a comma separated list of all prime numbers less than num • isPrime(intnum) • //return true if num is a prime number

  10. Arrays ArrayList String[] arr = new String[10];…//insert Strings into array…for(inti=0; i<arr.length; i++){System.out.println(arr[i]);} ArrayList<String> arrList= new ArrayList<String>();…//insert Strings into ArrayList…for(inti=0; i<arr.size(); i++){System.out.println (arrList.get(i));} Arrays vs. ArrayList

  11. Arrays ArrayList String[] arr = new String[10];…//insert Strings into array…for(String x : arr){System.out.println(x);} ArrayList<String> arrList= new ArrayList<String>();…//insert Strings into ArrayList…for(String x : arrList){System.out.println(x);} Arrays vs. ArrayList

  12. Arrays ArrayList Fixed length, set when it is createdMust keep track of last slot if array is not fullMust write code to shift elements if you want to insert or delete Shrinks and grows as neededLast slot is always arrList.size()-1Insert with justarrList.add(object)Delete with just arrList.remove(objectIndex) or arrList.remove(object) Arrays vs. ArrayList

  13. ArrayList methods • add(Object elem) • remove(int index) • remove(Object elem) • contains(Object elem) • isEmpty() • indexOf(Object elem) • size() • get(int index)

  14. Generics • ArrayList class is generic, which means it has a type parameter • Class header  public class ArrayList<E> • <E> is placeholder for any non-primitive type • ArrayList<String>  stores Strings • ArrayList<Integer>  stores ints • List is restricted to particular data type • Built-in safety

  15. The Jokes Get Pun-nier • What kind of music do Santa’s elves listen to the most? • What kind of musicians are Integers and Doubles? • Wrap music/Wrappers :P

  16. Auto-Boxing and -Unboxing • ArrayList must contain objects • NO PRIMITIVES • Objects usually start with upper case letter • String, Egg, Pokemon, Dog, etc. • Primitives usually start with lower case letter • int, double, boolean, etc. • Numbers must be boxed—placed in wrapper classes like Integer or Double—before insertion into an ArrayList

  17. Auto-Boxing and -Unboxing • Auto-boxing • Automatic wrapping of primitive types in their wrapper classes • Use intValue() or doubleValue() to retrieve the numerical value • Auto-unboxing • Automatic conversion of a wrapper class to its corresponding primitive type

  18. Auto-Boxing and –Unboxing Example ArrayList<Integer> arrList = new ArrayList<Integer>();arrList.add(4); //auto-boxing //4 is an int, wrapped in an //Integer before insertionint n = list.get(0); //auto-unboxing //Integer is retrieved //and converted to int

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