Guide to High School Computer Science
  • 💻Introduction
    • windows & Python Development
    • macOS & Python Development
    • Visual Studio Code Settings
    • Set up Github
    • Author Page
  • 🧠Prerequisite Skills
    • Keyboard Typing
    • Files & Directories
    • Use of Command Line
    • Git & GitHub
    • Markdown
    • Starting Your Python Project
  • 🐍Python Programming
    • 🍎Python Basics
      • What is Python?
      • Procedural Programming & Programming Paradigms
      • String Formatting
      • Data Types
      • Input & Output to Console
      • Working with Numbers
      • Useful Built-in Functions
      • Math & Random Module
      • Boolean Data Object
      • Comparison, Logical, and Membership Operators
      • If Statements
      • Binary Decisions
      • Multiple Decisions
      • Nested Conditions
      • [EXTRA] Bitwise Operators
      • [EXTRA] Python Style Guide
    • ⏮️Iterations
      • Introduction to While Loops
      • Infinite Loop
      • Controlling Your While Loops
      • Introduction to For Loops
      • For Loops w/ Numeric Sequences
      • For Loops w/ Strings & Lists
      • Iterable Functions w/ For Loops
    • 📦Collections
      • Strings
        • String Basics
        • String Indexing
        • String Slicing
        • String Operators & Functions
        • Basic String Methods
        • String Methods Extended
        • String Methods Document
      • Tuples & Lists
        • Tuples
        • List Basics
        • List are Mutable
        • Adding Items to a List
        • Removing Items from a List
        • Search & Reverse a List
        • List Comprehension
        • List Methods Document
      • Sets
      • Dictionary
      • How to Store Multiple Data Items
    • 💡Defining Functions
      • Functions
      • print() vs return
      • Pre-determined Arguments
      • Nested Functions
      • Map & Filter
      • [Extra] Dynamic Arguments
    • 💾File I/O
      • How to Save Text to an External File
      • Reading CSV in Python
      • Reading JSON in Python
    • 🔨Basic Python Projects
      • Basic Calculator
        • Improving the calculator
        • Exercise Set 1
        • Exercise Set 2
        • 💎Streamlit Application #1
      • Basic Password Generator
        • Exercise Set 3
        • Exercises Related to Math
        • 💎Streamlit Application #2
      • A To-Do Task List
    • ⏳Introduction to Algorithmic Thinking
      • Big-O Notation
      • Basic Algorithms
        • Linear Search
        • Binary Search
        • Basic Sorting Algorithms
      • Recursion
      • Brute Force Algorithms
      • Greedy Algorithm
        • Time on Task (CCC 2013 J4)
        • Dijkstra’s Algorithm
      • Divide and Conquer
        • Merge Sort
      • Dynamic Programming
    • 🤯Object Oriented Programming
      • Class & Objects (Definitions)
      • OOP in Python
      • Encapsulation
      • Polymorphism
      • Inheritance & Overriding
      • Override Magic Methods
      • Case Study: 2D Vectors
      • Case Study: Deck of Cards
      • Exercise
      • Abstract Data Types
      • Case Study: Static 1D Array From Java
    • Competitive Programming
      • Is This Sum Possible?
        • Is the dataset sorted?
        • Searching for a value
        • Determine if the difference between an integer from the array and the target value exists
        • Sorting Algorithms
        • Using Two Pointers
      • Two Sum - LeetCode
        • Generate all possible pairs of values
        • Subtract each value from the target, see if the difference exists in the list
      • Longest Common Prefix - LeetCode
        • Compare all possible prefixes
        • Create the longest common prefix with the direct neighbour
      • Length of Last Word - LeetCode
        • Compare all possible prefixes
      • Where can I go from one point to another?
      • Sample Outline
    • IB Recipe Book
  • 💾Python & Databases
    • Intro to Databases & Data Modeling
      • Common Data Types in SQL
      • Introduction to ERDs
      • Primary Keys and Foreign Keys
      • Database Normalization
    • What is SQL?
      • Getting Started
      • SELECT Queries
        • Selection with Conditions
        • Selection with Fuzziness
        • Selection and Sorting in Order
        • Selection without Duplicates
        • Selection with Limited Number of Outputs
      • AGGREGATE Queries
        • Counting Rows
        • Sum, Average, Min/Max Queries
        • Working with Aggregate Queries
        • Power of using Groups
        • Exercise
      • Interacting with Multiple Table
      • Inserting Data
      • External Resource
  • ☕Java Essentials
    • Basics
      • Starting Java
      • Data & Variables
      • Handling User Inputs & Type Conversion
      • Arithmetic
      • IPO Model
      • Basic Built-in Methods
      • Exercise Questions
    • Conditionals
      • Boolean Operators
      • Compare Strings
      • If Statements
      • If Else Statements
      • Making Multiple Decisions
      • Using Switch
      • Flowchart Symbols
      • Exercise Questions
    • Iterations
      • While Loops
      • For Loop
      • Exercises
    • Java Type Casting
    • Strings
      • Common String Practices
      • String Formatting
      • Java Special Characters
    • Collection
      • Arrays
      • For Each Loop
      • ArrayList
      • Exercise Questions
    • Static Methods
      • (Aside) Clearing your Console
    • Randomness in Java
    • Delayed Output in Java
    • Java Output Formatting
    • Java Style Guide
  • 🛠️JavaScript Programming
    • Our Programming Editor & Workflow
      • Hello, world!
      • Commenting & Variables
      • Data in JavaScript
      • Operators
      • String Formatting
      • Getting User Input
    • JavaScript Exercise Set 1
    • Making Decisions
      • Comparing Values
      • Combining Boolean Comparisons
      • Creating Branches
    • JavaScript Exercise Set 2
    • While Loops
      • Infinite While Loop
      • While Loops and Numbers
      • While Loops and Flags
      • While loops w/ Strings
    • JavaScript Exercise Set 3
    • Subprograms & Functions
      • Creating a Function in JavaScript
      • Function with Input and Assignable Output
    • JavaScript Exercise Set 4
  • 💾Topics in CS
    • Computer Environments & Systems
      • Computer Components
        • In-depth Explanations
      • File Maintenance
      • Computer & Safety
      • Software Development
      • Bits & Binary
    • Careers related to Computer Science
    • Postsecondary Opportunities
Powered by GitBook
On this page
  • A Basic Java Program w/ Variables
  • The 6 Data Types
  • Variables
  • Data Type and Their Storage Size
  • Constants
  • SOURCES
  1. Java Essentials
  2. Basics

Data & Variables

A Basic Java Program w/ Variables

class Main {
    public static void main(String[] args) {
        int age = 31;
        float temp = -2.5f;
        double large_decimal = 12345.6789;
        char grade = 'A';
        String name = "Mr. Park";
        boolean working = false;

        System.out.println("Age: " + age);
        System.out.println("Current Outside Temperature: " + temp);
        System.out.println("Large Decimal:" + large_decimal);
        System.out.println("Letter Grade: " + grade);
        System.out.println("Name: " + name);
        System.out.println("Are they working?: " + working);
    }
}

The 6 Data Types

In Java Programming, there are many datatypes we can work with. We will be analyzing 6 different datatypes.

Integer : int

Integer helps us to represent integer values in our program.

The int data type can store whole numbers from -2147483648 to 2147483647. We can use these values to do arithmetic operations.

Decimals : float

The float data type allows us to represent decimal based numbers. The values must end with a letter f. Example: float pi = 3.14f;

Longer Decimals : double

The double data type also allow us to represent decimal based numbers. The big difference between double and float is that a double variable is able to contain a larger value than float.

Text : String

The String data type is used to store a sequence of characters (text). String values must be surrounded by double quotes.

Single Character : char

The char data type is used to store a single character. The character must be surrounded by single quotes, like 'A' or 'c'.

True & False Values : boolean

For this, Java has a boolean data type, which can only take the values true or false.

Variables

Variables are labeled containers that helps to hold data in programming. The variables have labels so that we can reference them in our code. We can also update variables, create variables, and manipulate variables to help our code have functionality.

Variable Formatting

DATATYPENAME variable_label = VALUE;

All variables must have an explicit datatype stated, given a label name, and assigned a value. It must also have a semi-colon to end the line.

Variable Naming Conventions

  1. start with lowercase letters

  2. labels that have multiple words are either camelCased or use under_scores

  3. labels should not be ambiguous String a = "Park" is less descriptive than String last_name = "Park"

Data Type and Their Storage Size

Data Type
RAM Storage Size

int

32 bits

float

32 bits

double

64 bits

char

16 bits

string

depends on String object

boolean

1 bit

Constants

A constant variable is the one whose value is fixed and only one copy of it exists in the program. Once you declare a constant variable and assign value to it, you cannot change its value again throughout the program. (Tutorialspoint)

Java does not support constants, but we can use two keywords: static and final to mimic such behaviour.

  • static variables are created at compile, only one copy of them is available.

  • final variables cannot be modified after its creation

In basic programs we don't really have a need for these types of data.

SOURCES

PreviousStarting JavaNextHandling User Inputs & Type Conversion

Last updated 7 months ago

FUN FACT: boolean was named after a mathematician named

labels cannot be the same as the in Java

w3schools --

tutorialspoint --

☕
George Boole
built-in keywords
https://www.w3schools.com/java/java_data_types.asp
https://www.tutorialspoint.com/difference-between-constants-and-final-variables-in-java