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Week 4-5 Java Programming

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Loops What is a loop? Loop is code that repeats itself a certain number of times There are two types of loops: For loop Used when we know exactly how many times we want to loop for While loop Used when we dont exactly know how many times we want to loop for

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Loops For loop structure: for(int i = 0; i < #; i++) { code here; } Programmers conventionally start counting at zero (zero- based numbering) Replace the # with the number of times you want the code looped

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Loops For loop: Lets create a program that will print 1 through 100 using a for loop that loops 100 times for(int i = 0; i < 100; i++) { System.out.println(i + 1); }

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Loops While loop structure: while(boolean someBool) { code here; } Notice that the boolean someBool will need to be true in order for it to enter the while loop (it acts as an if/else staement), inside the code is where you want to make it so that someBool will eventually become false in order for it to exit the loop or else it will loop infinitely and crash.

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Loops While loop: In a while loop, there is a condition, the condition is a comparison between two values in which if turned false it will exit the loop, else it will loop until your computer runs out of memory (crash) Example: int age = 0; while(age < 20) {// (age < 20) is the condition System.out.println(age); age++;// age is increased by 1 with every }// loop

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Loop Example: Count to from 1 to 100. Would it be better if we used for loop or while loop in this case? Given a list of 100 numbers from 1 to 100, randomly placed. I want you to find where the number 40 is located starting from the beginning of the list. Would it be better if we used for loop or while loop in this case?

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Learning to count like a programmer Most programmers count starting from zero Be extra careful when counting in programming, when I ask for position 5, what it really means is 6 units from the left since 0,1,2,3,4,5 is 6 units. When using String functions such as stringName.substring(0,5) will get the letters from the 0 th position to the 4 th position because the last letter is EXCLUDED (its how this function is programmed) Example: String someString = Hello; someString.substring(0,3) will return Hel

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Object Oriented Programming OOP is a program model which is based on objects instead of actions. Objects contain methods and values, methods are the procedures and values are the data for the program. An object is an instance of a class and it only defines data it needs to be concerned with, the code will not be able to accidently access other program data. The idea of a class is that it is reusable not only by the program that it was initially intended for but also other object oriented programs. The concept of data class allows the user to create a new objects that havent already been defined in the language itself

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Creating an OOP Program Create an object and then use it in the main function WaterBottle.java WaterBottleMain.java WaterBottle.java contains the objects details and what we can do with the object WaterBottleMain.java is just a regular program (the one with the main header function) that we will use to implement the object WaterBottle

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Creating an OOP Program WaterBottle.java and WbMain.java

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Creating an OOP Program What is contained in an Object file? Constructor Default values for the object once its created and stored into memory for later use Accessor Methods are used to retrieve data about the object Keyword for Accessor Methods is get Mutator Methods are used to set data about the object Keyword for Mutator Methods is set

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Randomization There is no true random generator that exists in computer programming, only complex patterns. Eventually numbers will repeat itself. If you think about it, you can throw dice and the number that appears on top will be random. But in computer terms, the programmer must tell exactly how the dice will select the number, through a complex algorithm. Algorithm - A process or set of rules to be followed in calculations or other problem-solving operations, esp. by a computer.

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Randomization There is a complex algorithm implemented in Javas library, were going to be using this algorithm to obtain randomly generated numbers Since its in the library, well have to take it out of the library and into our code by using this command: import java.util.Random;

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Randomization Using the random command, well have to declare it like we do to data types like integers etc. We declare a random object by: Random myVar = new Random(); Now myVar is of type Random, well be using myVar to generate our random results

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Randomization How to use it: You can use it in various ways, we can store the random number that is generated into memory (by creating an integer variable and setting it to the random number) or simply just printing it Random myVar = new Random(); int myInt = 0; myInt = myVar.nextInt(100); This code will generate random numbers from 0-99 and store it into the variable myInt

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Dice Create Dice.java and DiceMain.java

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Arrays What are arrays? You can think of an array as a list This list can only contain one data type Before creating an array, you have to already know how much space your list should reserve Arrays are static which means it cannot be changed Once an array of a certain size is set, the size cant be changed which is why you must know exactly how much space you need before using an array

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Arrays How do we use arrays? Arrays are defined in Java by default, so all we have to do is declare it, we declare it by: int[] myVar = new int[5];// This reserves space for 5 integers Notice that weve added square brackets, this is how an array is declared, the new int[5]; means were creating room for 5 integers

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Arrays How we would use arrays: int[] myVar = new int[5]; myVar[0] = 1; myVar[2] = 3; myVar[1] = 10; myVar[3] = 6; myVar[4] = 600; Notice that we use the variable name followed by square brackets with a number inside, the number inside is the address number, it locates the space on the list and then assigns a value to the space Also notice that the number does not have to be in order, you can assign a value to the space however you like

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Arrays Instead of using: int[] myVar = new int[5]; We can use this if we already know the integers we want stored on the list int[] myVar = {10, 3, 1, 6, 600, 500, 200};