Brandon Rozek

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PhD Student @ RPI studying Automated Reasoning in AI and Linux Enthusiast.

Lecture for January 23

Java Class

In Java, your code must live in a class.

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

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

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);