An online markdown blog and knowledge repository.
Week 1: 16-May to 20-May 2022
A collection of draft, WIP, and straggler notes taken during class discussion, presentations, etc.
You Are A Software Developer! Get used to calling yourself this. We are all developers here, and the more often you say it the more of a reality it becomes. "Tech skills for a better life, community, and world." -Code Fellows Vision Mission: Guide people from all backgrounds to change lives through fast-paced, career-focused education. Shaping passionate learners with immersive training to meet industry needs and improve diversity." -Code Fellows Mission
Campus Director
Direct support to you while planning for your next career. Must graduate 401, submit a (stellar) resume, pass a qualifying moch behavioral interview (45 mins max) with post-interview feedback for improvement. DO NOT LEAVE THIS ON THE TABLE. Not a one-shot deal.
Connects alumni with 'partners' with Code Fellows, where CF manages resume passing and keeping alumni notified as to which partner(s) are viewing the CAP resume.
Prepare for reading a ton of documentation. Start getting good at extrapolating a solution from reading documentation and other resources. Put effort into exposure and practice throughout this class, and within tech. Slack DM Alex for short discussions or anything that is critically important. For longer discussions (30 mins+) schedule ahead of time w/ Alex. Lunch will always be from 1230 to 1330. Get code challenges out of the way 1st and DO NOT TAKE LONGER else you are doing yourself a dis-service. You have one job as a developer: SOLVE PROBLEMS, which can be an endless time suck. Do not refactor until you are done solving the problem. Goto Canvas and the Class Repo to keep up to date and help solving code problems, including class recordings (1-3 hrs after class to encode). FYI: React can work with other languages besides javascript. Spring MVC: Thymeleaf: Template engine. Assignments will re-open before mid-terms, then close for the remainder of the class. Final opportunity to submit assignments during 2nd half will be before final project week. Late work: Turn-in substantially completed work before deadlines, to avoid penalty when completed later. Do NOT worry about implementing tests in Code Challenge Day 1. While Alex is in Remo, he is available to get assistance/conversations.
Arrays should store like-data values.
Objects can store different data types.
Create objects multiple ways including let myObj = {}; and object instantiation of a class let myThingy = new Thingy([args],...)
DRY: Don't Repeat Yourself. Classes allow following this principal.
Strongly Typed Languages: Require declaring a Type (or Class).
Functional and Procedural languages include javascript: Run code top-to-bottom as a runtime language.
Compiled languages like Java are translated to run in a specific way, not just top-to-bottom.
Libraries: Do not utilize a 'main' function.
Protected, Public, and Private: Control access to classes and members.
Parameters: Abstract idea that the variables will eventually have values.
Arguments: Whatever you want to call the local variables you will use within the function.
Dot notation/object notation: Use '.' between objects and their members, child-objects, etc.
Escape character \: Use to enable use of a reserved character in a string.
Applications need an entry-point e.g. a 'main' function.
Libraries do not have an entry-point and are referenced by another App or other Libraries.
To execute java apps from command line: java appName.java But this performs the java runtime execution but it probably doesn't do a full compilation.
Compiler: javac.exe is an example. It just creates a 'build file' but does not execute it.
Always compile before pushing to your repo.
Probably the most commonly used types will be String and Int.
Hexadecimal values default to Int type, so be sure to cast to the correct type for the size of the Hex value.
CONSTANT_VALUES can be accessed outside of the defining class with: className.CONST_VAL;
Work within objects, using methods within those objects to get work done.
String Interpolation? NO Instead do: System.out.println("Maximum integer is: " + maxInt);
Terminology: Method (rather than Function) because we are working in a OOP language.
Short-cut declartion for float and double: 'f' and 'd'.
Expressions: Happen within parens ( expr... )
Need precision? Float (32-bit) over Decimal.
String type is a Class not a primitive type.
Characters 'char' are a special type that represent ASCII codes to display a specific single character.
char char1 + char char2 returns a 'string'.
Integer.parseInt(string): Converts a string into an integer.
Do not use '==' to compare/equality of objects, this includes String!
When comparing Types '==' will fail you so use {}.equals(other) instead.
Overflow: Wraps-around from MAX_VAL to MIN_VAL and vice-versa.
Two ways to create arrays:
int[] myArray = new int[10];
int[] myArray2 = {1,2,3};
Println(array) will return the reference address to the item in memory.
Common java utilities example: import java.util.____
Use StackOverflow and Google searches to find the import libraries you want/need rather than trying to wade through docs.oracle.com (don't get lost in the sauce).
Loops: FOR and WHILE
for(int i=0; i,myArr.length; i++) {
...
}
//use a boolean conditional because it will be easy to read
while(condition) {
incrementor/decrementor/condition-setter
...
}
For...Of
//for every value in :array do codeblock statements
for(type variable : array) {
codeblock;
}
//: is essentialy the "of" in the statement
//Inc/decrementor is not necessary here
Break: Break out of the parent looping structure. Continue: Move on with next iteration. Be aware: Procedural Debugging is a little different than Compiler debugging. Static: Can be applied to Methods and Variables.
Did I set the type properly? Is the method accessible? Is my method expecting the correct type or the caller sending the correct type as args? Do the number of params match? Does the method return anything or is it void and is the caller expecting that? Where am I in the code body? Am I within another method or at the class root?
Gradle (tomorrow). Today: JavaC.
> javac filename.java
Note: There are many different ways a whiteboarding interview and layout will work/go. Problem Domain: The problem the interviewer supplies. Test Cases: Given a good input, a good output is expected (with examples?). Includes Edge Cases where errors or other returns could happen. Algorithm / Logic description: Use arrows and verbose english to discuss how the logic should work. Pseudocode: Required during week 1, later is optional. If it helps you, use it. Actual Code: Big O: Effeciency of the algorithm. No actual code writing is required to get this right. Step Through / After-code: Talk through the code, visualizing the step-through following current and next values based on operations.
Whiteboarding software. Recommended by Code Fellows.
Whiteboarding software. Alex says Miro is better than Invision.
You may have to ask questions of the interviewer to better understand the problem. What are the inputs and outputs? What are the types? Consider drawing example in/outputs. Edge Cases: Update these throughout the interview. Consider questions about nulls, empty/undefined, various datatypes, and whether in-place or output new result.
Ask as many questions about the problem as you can early in the process: inputs, desired outputs, are objects required or okay to just build a new method, etc. Keep whiteboard neat, but use enough style to differentiate sections of the whiteboard. Use the software to create images/drawing shapes with labels to depict input(s), output, and then put the steps in between. Chat about the algorithm next. Still not code, rather describe the algorithm operation(s). Pseudo-code: With a visual and an algorithm, write pseudo-code to represent how the actual code would work. Big-O Notation: Creating a variable is O(1); Not creating any new structures so Space O(1); Time O(n). More Big-O: Mention the worst-case scenario O(n) in time for the algorithm and make an assertion about use of space. Testing Discussion: Describe which testing suites you would use, if/when purposely-failing tests, null/empty tests, and known-good (must pass) test methods. Remember to cover start and stop conditions if they are used. Talk-though the whiteboarding every step of the way. At any time throughout the process, tell the interviewer when you are going to stop and think through something briefly -- avoid uncomfortable and/or unexpected silence. Revisit the algorithm to ensure it matches your code. You can talk as you type and what you type. Ask the interviewer if they have any questions about what you've done so far and whether anything could be reviewed. If you want to use a built-in method you'd better know how it works! Testing: Mention JUnit Jupiter as the testing tools and the basic pass/fail requirement.
Do not have to use '.Equals()' when comparing non-objects. Do not overload a single method => DRY and single-responsibility. Public: Accessible everywhere within the current Project. Private: Limited access within a subset of the current Project (more on this later).
Experience and Exposure are going to help you getting through these problems. This problem was "Given an array, return an array with the middle index removed." Good question to ask: "Should the array be edited in-place or can I return a new array?" Another good question: "Do you have sample input I can use?" Another question regarding arrays: "If working with an odd-length array, should there be any special handling?" What do I know about arrays? They have a length; They are of a set size. Visual: Should reflect the algorith including input and result or output of the algorithm. Recursion: A separate iterating process than Looping. When thinking through the Algorithm:
When Pseudo-coding:
Solve the problem first then write the code.
$> gradle init which generates project files etc..gitignore file with your submitted work.Import using package.class.member or package.class.*
Arrange => Act => Assert
Arrange: Configure variables to prep for testing including test-inputs and expected outputs. Act: Call the function under test. Assert: Pass/Fail output based on expected return the function under test. Use the term "System Under Test" or 'sut' Create your test names to describe what the test is doing and expected output. Note: Empty Tests will PASS by default!
Make sure the language and SDK selection in Project Structure are correct. Do not use the Oracle SDK for this class. Run the tests after setting SDK and continue only if the tests pass.
ArrayList has built-in methods like .add and several others:
.get(n) accesses an element via the index number 'n'..set(n) modifies an element in place via index number 'n'..remove(n) removes an element via the index number 'n'..clear(); removes all elements from the array.String[] studentArray = new String[9]; // create new array of strings with capacity of 9
ArrayList<Integer> classSizes = new ArrayList<>(); // this is an object Type
This comes from a parent package to the ArrayList class.
Use like my_arrayList.addAll(Arrays.asList(my_other_array));
Has built-in methods like SORT that take an existing Array as an argument and sort it (in-place?).
CONDITIONAL instead of IF DEFINE functions instead of DECLARING them DECLARE variables
Question: Is this a sorted array? If so, should it stay that way?
Name your Package and Class the same thing.
Exporting a package: First line of package should be package package_name; to make it available to the rest of your code in your App.
Importing: Grab a single class import package_name.ClassName; or all members in a package import package_name.*;
Create a package to easily reuse code, including your own!
IntelliJ: rClick => New => Package. Create a new Class within the package_name folder.
Package Names are camelCase.
Class Names are PascalCase.
HashMaps aka Dictionaries aka Hash Tables aka Key-Value Stores.
HashMaps are good at storing retreivable, organized data.
Set extends HashMaps?
HashSet inclues member .addAll(ArrayList<>) to bulk-add an existing ArrayList.
Linked- versions of HashMaps and HashSets maintain order.
Good at handling: Counts, Lookups, and Uniqueness.
Measure Uniqueness!!
Quick Lookups!!
Count Instances!!
Maps accept a Key Value pairs as args.
Values belong to a specific Key.
KV Pairs need to be typed e.g. Key of type Integer, Value of type String.
Create a HashMap Example: HashMap<String, ArrayList<Boolean>> variableName = new HashMap<>();
Create a HashSet Example: HashSet<String> variableName = new HashSet<>();
Path: import java.nio.file.Path;
Paths: import java.nio.file.Paths;
Access, Read, track (counting instances): HashMap<String, Integer> myMap = new HashMap<>(); String[] items = {string, string, ...}; System.out.println(scannerInstance.nextLine());
Access: Path path_var = Paths.get(file_path_var);
Get Absolute Path: path_var.toAbsolutePath(); outputs the path in full of the path_var value.
Java's Scanner class has built-in methods that will be helpful.
Boolean .hasNextLine() returns true only if look-ahead to next line succeeds.
Remember to use RegEx101.com to help when regex is the right solution for finding strings in lines.
Scanner scanner = new Scanner(path);
scanner.hasNext();
scanner.nextLine();
Relative vs. Absolute file pathing:
/bin directory.Types include: Runtime Exceptions, IO Exceptions i.e. File System based.
try {
// run your might-throw-an-exception code here
myScanner = new Scanner(myPath);
}
catch (IDException ioe) {
// oopsie something bad happened in the try block
System.out.println("That file cnnot be scanned or was not found. File path is: " + myPath.toAbsolutePath());
ioe.printStackTrace();
System.exit(status_code);// status_code can be any integer but 0 is usually 'success'
// any other integer is 'failure of some type'
}
Multiple Catch blocks can be defined.
You will want to consider the following when creating a member:
gradle init and respond to questions e.g. library, java, groovy, new APIs, JUnit Jupiter.Note: Difference between an App and a Library? Apps have Main (an 'entry point').
Note: Sometimes the project directory must be removed and gradle init run again.
package bakery;
public class CinnamonRolls extends BakedGoods {
public boolean hasSwirl;
public CinnamonRolls( <parent-constructor-params>, boolean swirl) {
super(parent-param, ...);
hasSwirl = swirl;
}
}
When creating a bunch of objects, consider categorizing them and using ArrayList for storage in another object.
Public: The class you are working in can see all other access-modified members. Protected: Classes, Packages, Subclasses, and other Project-level items have access. Private: Only the defining Class can access these members. Default: Only the defining class or Package.
Note: Default is an optional modifier keyword.
Build your own constructor! Use 'public' to allow calling the Constructor from other modules. The term 'this' relates to the current scope. Multiple Constructors can be created with differing parameter lists.
public static final int MY_CONST = 1;
// use UPPER_SNAKE_CASE for constant properties
@override decorator.class... {
@override
public Stringn toString() {
return property.toString() + ...;
}
}
Create these to help ID:
Even very simple domain models will help simplify code development.
Bitmap Transformer! Create a very very very simple PhotoShop - edit images. Minimum Requirements:
Class TA Ben has done this project recently so he can help but will not give you the answer.
Groups of 3 will work on this lab. Assigned by Alex.
Whiteboard Only. Paired programming. Bookmark and save the Whiteboard Rubric! Timebox this assignment - strict!
./gradlew run --args strings...
To have your App accept other types (besides String[]), just define the args parameter list in Main method.
./gradlew run --args %arg_types_defined_by_main_method%
Linked lists and Trees are very common interview/technical questions. Nested objects (nodes) with links REF'ing other Nodes.
Blocks of space will get consumed by bits, bytes, and Big/Little endian storage types and methods.
Traverse a LL:
Linked List Node
// Nodes are selfish and only care about their State
// Member next is not even assigned!
public class Node {
public int value;
public Node next; // defaults null
public Node(int value) {
this.value = value;
}
}
Linked List Class
public class LinkedList {
Node head = null; // no LLNodes so force null so callers know list is empty
Node tail = null; // OPTIONAL
public void insert(int value) {
// create a new Node
}
public Boolean includes(int value) {
// does one of the LLNodes have this value?
return false; // default return
}
// override toString
@Override
public String tostring() {
return " ";
}
}
Discussion of BigO analysis of Singly-Linked Lists.
Measured in milliseconds so BigO is measured relatively in terms of efficiency.
Remember ONE thing: Additional Allocation => Should I measure my input?
Aliasing: alias ls='ls -la' causes ls to always run ls -la.
[X] Mess with this to streamline my processes.
String.concat(stringOne).concat(stringTwo), StringBuilder class, String.format("%s %n", stringOne), String.join(str1, str2, ...)).Assignments Due Thursday:
Get-Ahead Work Items As Time Permits:
Baeldung String Concatenation Methods
IntelliJ Live Templates
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