Part 1

Input is always read as a string

"string literal"

String message = scanner.nextLine();

Variable's Type Persists

(but, int➡️double OK. not the other way around)

Boolean.valueOf("true" and "TRue")

System.out.println("Four: " + (2 + 2));

int / int = int

type casting : (double) int / int = double

{code block}

< 0 / 0-49 / 50-59 등 범위 다룰 때 : 0-49는 언뜻 봐서 comparison 2개가 요구되는 것처럼 보이지만, else if 앞뒤로 이미 처리한게 있는지 확인하면 깔끔해짐!

comparison is affected by how much information a variable can hold : String ∞ 🆚 int, double, 유한

Conditional : find the most demanding condition!!!!!

else문 : 한 줄이라고 {} 생략 안 됨!!!

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Part2

Math.sqrt의 결과는 항상 double

Break == Exit the Loop

Continue == return to the beginning of the Loop

Clarity : One part, One Task

본질(원형 먼저), 그 뒤에 조건 덧붙임! 🗯️"clac avg? get the sum & count ready!"

Execution simulate : at each point the condition i < 4 is evaluated.

PROGRAM : one piece at a time.

기능(Task)에 맞게 구조(Structure)를 짜라.

Methods cannot be defined e.g. inside other methods.

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Part3 : csv를 split(",")해서 Array를 거쳐서 ArrayList에 add()한 뒤, for Each : 로 iterate하여 필요한 결과값을 도출한다.

Array, ArrayList, String 모두 Reference type

Variables in Java : 1️⃣value type (actual val, limited amount) 2️⃣ Reference type

ArrayList assumes that all the variables contained in it are reference types.

remove(index) value type할꺼면 명시해라

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Part4

If a method receives as parameters all the variables whose values it uses, it can have a static modifier.

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Part5 : OOP is Abstracting; a program is built from small and distinct objects that work together

Object-oriented programming is primarily about isolating concepts into their own entities or, in other words, creating abstractions.

Constructor Overloading : 2 (or more) constructors in a class

a special case (특수/보편 관계?) ➡️ Call!

🛑 If a constructor calls another constructor, the constructor call must be the first command in the constructor.

Private variable can be accessed from all the methods contained by that class. (diff Object 👌)

.equals의 디폴트값: 그냥 ==처럼 refer val 끼리 비교함.

Every Class inherits the class Object (그래서 누구나 equals, toString 쓸 수 있는 거)

The contains() method of a list uses the equals method of the object type

equals(Object) always!!!

const === final : cannot be modified after they have been set in the constructor.

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Part 6

잘 변하지 않는 특징들을 field로, 상황에 따라 변하는 값은 그냥 getCalcVal() method로!

set of words??

The set is a clear distinct "concept"/ abstraction. ➡️ potential objects ➡️separating the concept into a class of its own.

1️⃣Proceed with small steps

• Try to separate the program into several sub-problems and work on only one sub-problem at a time
• Always test 과정중에, test solution to the sub-problem
• Recognize the conditions that require the program to work differently. (핵심 조건 뽑아내기)

2️⃣ Write as "clean" code as possible

• Indent your code
• Use descriptive method and variable names
• Don't make your methods too long, not even the main method
• Do only one thing inside one method
• Remove all copy-paste code
• Replace the "bad" and unclean parts of your code with clean code

As a corollary, a program that's broken is rarely fixed by adding more code to it.

String의 반댓말은 null이다.

stringTest tells it's a test class.

each method tests an individual unit.

Only checked existence of wanted functionality ? narrow view !!

CHECK that UNWANTED behavior doesn’t occur.

Gather together the things that change for the same reasons. Separate those things that change for different reasons.

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Part 7

OOP - structure formed by the data(자체)

Procedural - formed by functionality(기능)

Methods without the static modifier are instance methods. Methods with the static modifier are class methods