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If you’re looking to learn a programming language that’s cross-platform and easily accessible, Java is one of the most practical languages out there. This handy cheat sheet helps you keep track of the basics while you begin to learn.

Java has been around for quite some time and it’s one of the most widely used languages when it comes to web apps, applets, and even some Android app development. This cheat sheet, from Princeton University’s Introduction to Programming in Java course, makes a great reference for the basics you need to know, like structure, input/output, data types, and functions. Check out the the link below to dig a little deeper into Java at Princeton University’s web site.


This appendix summarizes the most commonly-used Java language features in the textbook. Here are the APIs of the most common libraries.

Hello, World.

Hello, World in Java

Editing, compiling, and executing.

Compiling Hello, World in Java

Built-in data types.

Built-in types of data

Declaration and assignment statements.

Assignment statements


int data type

Integer expressions

Floating-point numbers.

double data type

double expressions


boolean data type

Boolean operators

Comparison operators.

Comparison operators

Comparison examples

Parsing command-line arguments.

parsing Command-line arguments

Math library.

Math library API

Expressions that use Java library methods

The full java.lang.Math API.

Type conversion.

Type conversion

If and if-else statements.

If-else statements

Nested if-else statement.

Nested if-else statements in Java

While and for loops.

While loop       For loop

While and for loops in Java

Break statement.

Break statement in Java

Do-while loop.

Do-while loop in Java

Switch statement.

Switch statement in Java


An array

Compile-time initialization.

Compile-time initialization of arrays

Typical array-processing code.

Typical array-processing code

Two-dimensional arrays.

2D array

Compile-time initialization.

2D array compile-time initialization

Ragged arrays.

Ragged arrays

Our standard output library.

Standard output API

The full StdOut API.

Anatomy of printf

Formatting codes for printf

Our standard input library.

Standard input API

The full StdIn API.

Our standard drawing library.

Standard drawing API

The full StdDraw API.

Our standard audio library.

Standard audio API

The full StdAudio API.

Redirection and piping.

Redirecting standard output                Redirecting standard input



Anatomy of a function

Example functions

Libraries of functions.

Library abstraction

Our standard random library.

Standard random

Our standard statistics library.

Standard statistics

Using an object.

Using an object

Creating an object.

Instance variables.

Anatomy of instance variables


Anatomy of a constructor

Instance methods.

Anatomy of an instance method


Anatomy of a class

Object-oriented libraries.

Object-oriented library abstraction

Java’s String data type.

String library API

The full java.lang.String API.

String operations

Note: the java.lang.StringBuilder API is similar, but StringBuilder supports some operations more efficiently than String (notably, string concatenation) and some operations less efficiently (notably, substring extraction).

Java’s Color data type.

Color library API

The full java.awt.Color API.

Our input library.

Input API

The full In API.

Our output library.

Output API

The full Out API.

Our picture library.

Picture API

The full Picture API.

Compile-time and run-time errors.

Here’s a list of errors compiled by Mordechai Ben-Ari. It includes a list of common error message and typical mistakes that give rise to them.