Java is a language

Java is a language that promises to run everywhere (that supports the Java runtime). It is a language that has a syntax. It is a language some people use. It is a language I'm not really excited about.

File Structure

Java follows a pretty basic schema, where each class is located in its own files which shares the same name.

Example: public class HelloWorld { ... } would be found in HelloWorld.java

Semantics && Syntax

Java is a object oriented langues, meaning it is based around classes.

Variables

Variables are defined using the type followed by an identifier.

SomeClass myClass;

Assigning a value to a variable is done by the use of the = symbol.

myClass = new SomeClass();

Key words

TODO: labels (break search)

• class: define a class
• new: instantiate a new instance of a class
• public: denotes public visibility
• private: denotes private visibility
• try: wraps code that might throw an exception
• catch: catches the exception thrown in the try block
• finally: wraps code that always runs after the try catch block (even if there is a return statement before)
• while: loop a code block until a condition is met (evaluates at the beginning)
• do: loop a code block until a condition is met (evaluates at the end)
• break: interrupt a loop
• final: used to declare const values (value cannot be changed)

Primitive datatypes

• byte: 8 bit
• short: 16 bit integer
• int: 32 bit integer
• long: 64 bit integer
• float: 32 bit floating point (IEEE 754)
• double: 64 bit double precision floating point
• boolean: true or false

Typecasting

Java allows for safely cast from a smaller space to a larger space without explicit casting.

Example: byte -> short -> int

Operands

• +: addition
• -: subtraction
• *: multiplication
• /: division
• %: modulo (rest of division)
• ++: increment by one
• --: decrement by one
• /=: divide and assign the result
• >: larger then comparison
• ||: logical or (as in either x or y)

Comments

Doc comments contain general information about the program and it's functionality. These can include:

• @author
• @version
• @param
• @return
• @throws
• {@link}
• {@docRoot}

Example:

/** 
 * A Java program.
 * 
 * @author  Thomas P. (thomas@example.com)
 * @version 1.01, 09/2025
 */ 

Inline comments are commonly used to provide some context to the reader. Example:

// This implementation is trash. 

Arrays

Error handling

Exception

When to throw an Exception:

• The application logic encounters an issue
• You can handle it gracefully (even if "graceful" means printing an error and exiting)

Error

When to throw an Error:

• The JVM runtime system is compromised
• There's nothing reasonable the application can do

Tooling

OpenJDK: The Open Java Development Kit is an implementation of Java Standard Edition. It encompasses tools and library's required to work-on and compile Java projects like:

• javac: The Java transpiler, which is used to compile files with a .java ending to files with a .class ending. Files with the .class ending get interpreted and executed by the Java runtime.
• java: The Java runtime. To execute a program run java {ProgramName} ({ProgramName} represents the entry class of the program).
• javadoc: Used to auto-generate HTML-Docs of a given program by referencing the doc comments.