Website snapshot

content/ta/spring2018/cpsc220/jan23.md

@@ -0,0 +1,92 @@
+# Lecture for January 23
+
+## Java Class
+
+In Java, your code must live in a class.
+
+```java
+public class NameOfClass {
+  public static void main(String[] args) {
+    // All program code
+  }
+}
+```
+
+It is important that `NameOfClass` is named meaningfully for the code. It is convention to use CamelCase when using classes. (Capitalize your class names!)
+
+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`.
+
+`public` means that any other piece of code can reference it.
+
+`void` means that the method returns nothing
+
+`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.
+
+`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.
+
+If you noticed `String` is a class, it is not a primitive type. This is denoted in Java by having it capitalized.
+
+## Arithmetic Expressions
+
+There is an order of operations in programming as well. It goes like this:
+
+1. Parenthesis
+2. Unary Operations
+3. *, /, %
+4. +, -
+
+And from there you read from left to right.
+
+## Constant Variables
+
+These are variables that can never be changed
+
+```java
+final int MINUTES_PER_HOUR = 60
+```
+
+The keyword `final` indicates to the Java compiler that it is a constant variable.
+
+By convention, constants are in all caps with underscores being separated between the words
+
+
+
+## Java Math Library
+
+There are some arithmetic expressions that we want to be able to do and we cannot achieve that simply with the standard operations
+
+| Method         | Description                   |
+| -------------- | ----------------------------- |
+| Math.sqrt(x)   | square root                   |
+| Math.abs(x)    | absolute value                |
+| Math.pow(a, b) | exponentiation $a^b$          |
+| Math.max(a, b) | returns the maximum of a or b |
+| Math.min(a, b) | returns the minimum of a or b |
+| Math.round(x)  | rounds to the nearest integer |
+
+## Example: Finding Areas
+
+```java
+public class MoreVariables
+  public static void main(String[] args) {
+  	// Decrate a variable
+  	int x;
+  
+  	// Initialize ia variable
+  	x = 5;
+  
+  	// Area of a square
+  	int squareArea = x * x;
+  	System.out.println("Area of a square: " + squareArea);
+  	double newSquare = Math.pow(x, 2);
+  	System.out.println("Area of square: " + newSquare);
+  
+  	// Area of Circle
+  	final double PI = 3.14159;
+  	double radius = 3;
+  	double circleArea = radius * radius * PI;
+  	System.out.println("Area of circle: " + circleArea);
+  	
+}
+```
+