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92 lines
2.6 KiB
Markdown
92 lines
2.6 KiB
Markdown
# Lecture for January 23
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## Java Class
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In Java, your code must live in a class.
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```java
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public class NameOfClass {
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public static void main(String[] args) {
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// All program code
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}
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}
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```
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It is important that `NameOfClass` is named meaningfully for the code. It is convention to use CamelCase when using classes. (Capitalize your class names!)
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All methods have a method signature, it is unique to it. For main it is the words `public static void` and the argument `String[] args`.
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`public` means that any other piece of code can reference it.
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`void` means that the method returns nothing
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`main` is the name of the method. It is important to have `main` since that tells the Java Interpreter where to start in your program.
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`String[] args` is the command line arguments inputted into the program. For this part of the class, we don't need to worry about it.
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If you noticed `String` is a class, it is not a primitive type. This is denoted in Java by having it capitalized.
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## Arithmetic Expressions
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There is an order of operations in programming as well. It goes like this:
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1. Parenthesis
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2. Unary Operations
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3. *, /, %
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4. +, -
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And from there you read from left to right.
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## Constant Variables
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These are variables that can never be changed
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```java
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final int MINUTES_PER_HOUR = 60
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```
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The keyword `final` indicates to the Java compiler that it is a constant variable.
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By convention, constants are in all caps with underscores being separated between the words
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## Java Math Library
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There are some arithmetic expressions that we want to be able to do and we cannot achieve that simply with the standard operations
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| Method | Description |
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| -------------- | ----------------------------- |
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| Math.sqrt(x) | square root |
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| Math.abs(x) | absolute value |
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| Math.pow(a, b) | exponentiation $a^b$ |
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| Math.max(a, b) | returns the maximum of a or b |
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| Math.min(a, b) | returns the minimum of a or b |
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| Math.round(x) | rounds to the nearest integer |
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## Example: Finding Areas
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```java
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public class MoreVariables
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public static void main(String[] args) {
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// Decrate a variable
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int x;
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// Initialize ia variable
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x = 5;
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// Area of a square
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int squareArea = x * x;
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System.out.println("Area of a square: " + squareArea);
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double newSquare = Math.pow(x, 2);
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System.out.println("Area of square: " + newSquare);
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// Area of Circle
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final double PI = 3.14159;
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double radius = 3;
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double circleArea = radius * radius * PI;
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System.out.println("Area of circle: " + circleArea);
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}
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```
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