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Published byFerdinand Stone Modified about 1 year ago

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PrimesFactory Lab Laugh if you get the pun

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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?

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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

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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...

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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

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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...

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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

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PrimesFactory Three important methods 1.Calculate the prime factorization of any number 2.Print a list of all prime numbers 3.State whether or not a given number is a prime number

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PrimesFactory Three important methods 1.getPrimeFactors(int num) //returns an ArrayList with all of the prime factors of num 2.listPrimesUpTo(int num) //returns a comma separated list of all prime numbers less than num 3.isPrime(int num) //return true if num is a prime number

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Arrays vs. ArrayList ArraysArrayList String[] arr = new String[10]; … //insert Strings into array … for(int i=0; i

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

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

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

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Generics ArrayList class is generic, which means it has a type parameter ◦ Class header public class ArrayList is placeholder for any non-primitive type ◦ ArrayList stores Strings ◦ ArrayList stores ints List is restricted to particular data type Built-in safety

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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

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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

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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

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

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