IronCodeMan

Concepts for Java

Java is a versatile, object-oriented programming language developed by Sun Microsystems (now owned by Oracle) in the mid-1990s. It's designed to be platform-independent, allowing developers to write code once and run it on any device or operating system that supports Java. Java's key features include its robustness, as it provides automatic memory management through garbage collection, strong type safety, and exception handling. It also offers platform independence through its "write once, run anywhere" philosophy, achieved by compiling Java code into bytecode that can run on any Java Virtual Machine (JVM). Additionally, Java boasts a rich standard library, extensive tooling support, and a large ecosystem of frameworks and libraries, making it popular for developing enterprise-level applications, mobile apps (with Android), web servers, and more.

Print Text

class HelloWorld {
  public static void main(String[] args) {
    System.out.println("Hello World!");
  }
}

Comments

// one line comment

/*
multi 
line 
comment
*/

Variables

int carCount = 2;
String name = "Joe";
boolean isPurple = true;

Data Types

int carCount = 2;
int age = 15;
short seaLevel = -10000;
long usBudget = 11000000000L;
long lightSpeed = 11799312874L;
float myGPA = 3.45f;
double piValue = 3.14159265;
char lastLetter = 'Z';
boolean isMale = true;
String myName = "Joe";

Math Op

int carCount = 6;
int truckCount = 3;

int total = carCount + truckCount;
System.out.println(total);

int subtract = carCount - truckCount;
System.out.println(subtract);

int multiple = carCount * truckCount;
System.out.println(multiple);
 
int divisble = carCount / truckCount;
System.out.println(divisble);
 
// performs division and gets remainder which is 0
int modulo = carCount % truckCount;
System.out.println(modulo);

Math Functions

import java.lang.Math;

double power = Math.pow(3.0, 6.0);
System.out.println(power);

double root = Math.sqrt(16.0);
System.out.println(root);

double floorVal = Math.floor(3.14);
System.out.println(floorVal);

double ceilVal = Math.ceil(4.3);
System.out.println(ceilVal);

double roundVal = Math.round(3.4);
System.out.println(roundVal);

// random number from 0 to 100
int ranNum = (int)(Math.random() * 101);
System.out.println(ranNum);

If/Else

int carCount = 6;

if (carCount > 3) {
  System.out.println("More than three cars");
} else if (carCount == 3) { 
  System.out.println("Equal to three cars");
} else {
  System.out.println("Less than three cars");
}

Ternary

int carCount = 3;

String result = (carCount > 2) ? "Yes" : "No";
System.out.println(result);

Switch

int carCount = 3;

switch (carCount) {
  case 1:
    System.out.println("One car");
    break;
  case 2:
    System.out.println("Two cars");
    break;
  case 3: 
    System.out.println("Three cars");
    break;
  default:
    System.out.println("More than three");
}

Functions

static int handleCars(int cars, int wheels) {
  int total = cars * wheels;
  return total;
}
    
int result = handleCars(3, 4);
System.out.println(result);

Interpolation

String name = "Joe";
String car = "Mazda";
String result = String.format(
  "%s drivers a %s", name, car
);
System.out.println(result);

Type Casting

import java.lang.Math;

public static String squareA(int length) {
  double result = (double)(Math.pow(length, 2));
  String strResult = String.valueOf(result);
  return strResult;
}

String squareL = "4";
int convertedVal = Integer.valueOf(squareL);
String area = squareA(convertedVal);
System.out.println(area);

Date and Time

import java.util.Date;
import java.util.Calendar;
import java.text.SimpleDateFormat;

// epoch time
long milliTime = System.currentTimeMillis();
System.out.println(milliTime );

Calendar cal=Calendar.getInstance();

// current year
int year = cal.get(Calendar.YEAR);
System.out.println(year );

// current month
int month = cal.get(Calendar.MONTH) + 1;
System.out.println(month );

// formatted date
String pattern = "MM/dd/yyyy";
SimpleDateFormat fullDate = 
  new SimpleDateFormat(pattern);

String formattedDate = 
  fullDate.format(new Date());

System.out.println(formattedDate );

Classes

import java.util.ArrayList;

class Cars {
  protected ArrayList<String> carList =
    new ArrayList<>();

  public void addCar(String car) {
    carList.add(car);
  }
  public void removeFirst() {
    carList.remove(0);
  }
  public String getFirstVal() {
    if(carList.size() > 0) {
      return carList.get(0);    
    }
    return "";
  }
  public static void main(String[] args) {
    Cars newList = new Cars();
    newList.addCar("Honda");
    newList.addCar("Mazda");
    newList.addCar("Toyota");
    newList.removeFirst();
    
    String firstCar = newList.getFirstVal();
    System.out.println(firstCar);
  }
}

Inheritance

class User {
  protected String username;
  protected String password;
  
  public User(
    String username,
    String password
  ) {
    this.username = username;
    this.password = password;  
  }
}

class Admin extends User {
  protected String Id;
  
  public Admin(
    String username,
    String password,
    String id
  ) {
    super(username, password);
    this.Id = id;
  }
  
  public String getUsername() {
    return this.username;
  }
  
  public String getAdminID() {
    return this.Id;
  }
}

class Test {
  public static void main(String[] args) {
    Admin newAdmin = new Admin(
      "alpha0",
      "pw1",
      "1FE"
    );
    System.out.println(
      newAdmin.getUsername()
    );
    System.out.println(
      newAdmin.getAdminID()
    );
  }
}

Method Overload

class UserForm {
  public String formA = "alpha";
  public String formB = "beta";
  public String formC = "gamma";
  public String formD = "epsilon";
  
  public String getForm(int age) {
    if (age > 65) {
      return formA;
    }
    return formB;
  }
  
  public String getForm(String id) {
    if (id == "1FE") {
        return formA;
    }
    return formC;
  }
  
  public String getForm(
    boolean isMilitary,
    boolean isNasa
  ) {
    if (isMilitary || isNasa) {
      return formD;
    }
    return formA;
  }
}

UserForm form = new UserForm();
int myAge = 67;
String myId = "1FE";
boolean veteran = false;
boolean nasa = true;

String form1 = form.getForm(myAge);
String form2 = form.getForm(myId);
String form3 = form.getForm(veteran, nasa);

System.out.println(form1 );
System.out.println(form2 );
System.out.println(form3 );

Abstract Class

abstract class Animation {
  public abstract void walk();
  public abstract void run();
  public abstract void idle();
}

class Human extends Animation {
  public void walk() {
    System.out.println("Human walks" );
  }
  public void run() {
    System.out.println("Human runs" );
  }
  public void idle() {
    System.out.println("Human idles" );
  }
}

class Zombie extends Animation {
  public void walk() {
    System.out.println("Zombie walks" );
  }
  public void run() {
    System.out.println("Zombie runs" );
  }
  public void idle() {
    System.out.println("Zombie idles" );
  }
}

Human player = new Human();
player.walk();

Zombie boss1 = new Zombie();
boss1.run();

Static Class

import java.lang.Math;

public static class Helper {
  public static double CircleA(int radius) {
    double power = Math.pow(radius, 2);
    return (double)(3.14 * power);
  }
    
  public static double SquareA(int length) {
    return (double)(Math.pow(length, 2));
  }
}
  
double circle = Helper.CircleA(3);
System.out.println(circle );
    
double square = Helper.SquareA(4);
System.out.println(square );

Arrays/Lists

String[] names = {"Joe", "Alex", "Bob"};
names[1] = "Tom";
String name = names[1];
int numItems = names.length;

System.out.println(name);
System.out.println(numItems);

Array Methods

import java.util.ArrayList;

// adds a new element
ArrayList<String> cars = new ArrayList<>();
cars.add("Honda");
cars.add("Mazda");
cars.add("Toyota");

// total number of element
int initLength = cars.size();
System.out.println(initLength );

// get element at index one
String secondCar = cars.get(1);
System.out.println(secondCar );

// removes element one
cars.remove(1);
System.out.println(cars.get(1) );

// becomes empty
cars.clear();
System.out.println(cars.size());

Concatenation

import java.util.Arrays;

String[] carListKr =
  {"Kia", "Hyundai", "Daewoo"};

String[] carListJp =
  {"Honda", "Mazda", "Toyota"};

String[] combined = Arrays.copyOf(
  carListKr, 
  carListKr.length + carListJp.length
);

System.arraycopy(
  carListJp,
  0,
  combined,
  carListKr.length,
  carListJp.length);

System.out.println(combined[1]);
System.out.println(combined[4]);

Sort Method

import java.util.ArrayList;
import java.util.Collections;

ArrayList<Integer> ages = new ArrayList<>();

ages.add(5);
ages.add(3);
ages.add(1);
ages.add(6);
ages.add(7);
ages.add(4);
ages.add(19);

Collections.sort(ages);

for (int i : ages) {
  System.out.println(i);
}

Objects

class User {
  public String first;
  public String last;
  public int age;
  public boolean retired;
  public String[] carBrands;
  
  public User (
    String first,
    String last,
    int age,
    boolean retired,
    String[] carBrands
  ) {
    this.first = first;
    this.last = last;
    this.retired = retired;
    this.carBrands = carBrands;
  }
  
  public String fullName() {
      return String.format("%s %s", first, last);
  }
}

String[] brands = {"Mazda", "Toyota"};
User user = new User (
  "Joe",
  "Doe",
  23,
  false,
  brands
);

System.out.println(user.first);
System.out.println(user.carBrands[1]);
System.out.println(user.fullName());

Maps (Key/Value)

import java.util.*;

Map<String, String> carMap = new HashMap<>();
carMap.put("Joe", "Toyota");
carMap.put("Bob", "Mazda");
carMap.put("Tom", "Ford");

System.out.println(carMap.get("Tom") + "\n");

carMap.remove("Tom");
System.out.println(carMap.containsKey("Tom"));

Sets

import java.util.*;

Set<String> cars = new HashSet<String>();
cars.add("Mazda");
cars.add("Toyota");
cars.add("Honda");

System.out.println(cars.contains("Honda") );

cars.remove("Honda");
System.out.println(cars.contains("Honda"));

Stack

import java.util.*;

ArrayList<String> cars = new ArrayList<>();
cars.add("Mazda");
cars.add("Toyota");
cars.add("Honda");

System.out.println(cars.get(cars.size() - 1));

cars.remove(cars.size() - 1);
System.out.println(cars.get(cars.size() - 1));

Queues

import java.util.*;

ArrayList<String> cars = new ArrayList<>();
cars.add("Mazda");
cars.add("Toyota");
cars.add("Honda");

System.out.println(cars.get(0));

cars.remove(0);
System.out.println(cars.get(0));

Linked List

import java.util.*; 

class Node {
  public String value;
  public Node next;
  
  public Node(String value) {
    this.value = value;
  }
}

class LinkedList {
  
  public Node head = null;
  
  public void addValue(String val) {
    Node newNode = new Node(val);
    if (this.head == null) {
      this.head = newNode;
    } else {
      Node current = this.head;
      while(current.next != null) {
        current = current.next;
      }
      current.next = newNode;
    }
  }
  
  public String returnHead() {
    return this.head.value;
  }
  
  public void traverse() {
    Node current = this.head;
    while(current != null) {
      System.out.println(current.value );
      current = current.next;
    }
  }
  public static void main(String[] args) {
    LinkedList carList = new LinkedList();
    carList.addValue("Mazda");
    carList.addValue("Toyota");
    carList.addValue("Honda");
    
    System.out.println(carList.returnHead() );
    carList.traverse();
  }
}

Graphs

import java.util.*; 

class Graph {
  public Map<String, ArrayList<String>>
    graphMap = new HashMap<>();
  
  public void addNode(String val) {
    ArrayList<String> tempArr = 
      new ArrayList<>();

    graphMap.put(val, tempArr);
  }
  
  public void addVertices(
    String node1, String node2
  ) {
    ArrayList<String> tempArr = 
      new ArrayList<String>();
    
    if(graphMap.containsKey(node1) == false) {
      graphMap.put(node1, tempArr);
    }
    if(graphMap.containsKey(node2) == false) {
      graphMap.put(node2, tempArr);
    }

    graphMap.get(node1).add(node2);
    graphMap.get(node2).add(node1);
  }

  public void breadthTraverse(String start) {
    ArrayList<String> queue =
    new ArrayList<String>();

    queue.add(start);
    Map<String, Boolean> visited =
      new HashMap<>();

    visited.put(start, true);
    
    while(queue.size() > 0) {
      String val = queue.get(0);
      System.out.println(val );

      queue.remove(0);
      ArrayList<String> tempArr =
        graphMap.get(val);

      for (int i = 0; i < tempArr.size(); i++) {
        String tempKey = tempArr.get(i);
        if(
          visited.containsKey(tempKey
        ) == false) {
          queue.add(tempKey);
          visited.put(tempKey, true);
        }
      }
    }
  }

  public void depthTraverse(String start) {
    ArrayList<String> stack =
      new ArrayList<>();

    stack.add(start);

    Map<String, Boolean> visited =
      new HashMap<>();

    visited.put(start, true);
    
    while(stack.size() > 0) {
      String val = stack.get(stack.size() - 1);
      System.out.println(val );
      stack.remove(stack.size() - 1);
      ArrayList<String> tempArr =
        graphMap.get(val);

      for (int i = 0; i < tempArr.size(); i++) {
        String tempKey = tempArr.get(i);
        if(
          visited.containsKey(tempKey) == false
        ) {
            stack.add(tempKey);
            visited.put(tempKey, true);
        }
      }
    }
  }

  public static void main(String[] args) {
    Graph newGraph = new Graph();
    newGraph.addNode("a");
    newGraph.addVertices("a", "b");
    newGraph.addVertices("a", "c");
    newGraph.addVertices("b", "d");
    newGraph.addVertices("b", "e");
    newGraph.addVertices("d", "f");
    newGraph.addVertices("d", "g");
    newGraph.addVertices("d", "h");
    newGraph.addVertices("e", "i");
    newGraph.addVertices("e", "j");
    newGraph.breadthTraverse("a");
    newGraph.depthTraverse("a");
  }
}

For Loops

import java.util.ArrayList;

ArrayList<String> names = new ArrayList<>();
names.add("Joe");
names.add("Alex");
names.add("Bob");

for (int i = 0; i < names.size(); i++) {
  System.out.println(names.get(i) );
}

While Loops

import java.util.ArrayList;

ArrayList<String> carList = new ArrayList<>();
carList.add("Mazda");
carList.add("Toyota");
carList.add("Honda");

while(carList.size() > 0) {
  System.out.println(carList.get(0) );
  carList.remove(0);
}

System.out.println(carList.size());

Loop Breaks

import java.util.ArrayList;

ArrayList<String> cars = new ArrayList<>();
cars.add("Toyota");
cars.add("Honda");
cars.add("Mazda");

for (int i = 0; i < cars.size(); i++) {
  if (cars.get(i) == "Honda") {
    String result =
      String.format("Found at index %d", i);
    System.out.println(result);
    break;
  }    
  String result =
    String.format("Visited index %d", i);
  System.out.println(result);
}

Recursion

import java.util.ArrayList;

public static int getSum(ArrayList<Integer> arr) {

  if (arr.size() == 0) return 0;
  int firstVal = arr.get(0);
  arr.remove(0);
  System.out.println(firstVal );
  
  return firstVal + getSum(arr);
}

ArrayList<Integer> testArr = new ArrayList<>();
testArr.add(1);
testArr.add(2);
testArr.add(4);
testArr.add(5);

int sum = getSum(testArr);
System.out.println(sum );

Regex Words

import java.util.regex.Matcher;
import java.util.regex.Pattern;

Pattern pattern = Pattern.compile(
  "(\\w+)",
  Pattern.CASE_INSENSITIVE
);

String phrase = "I am legend";
Matcher match = pattern.matcher(phrase);
String result = match.find() ?
  match.group(1) : "";

System.out.println(result);

Regex Numbers

import java.util.regex.Matcher;
import java.util.regex.Pattern;

Pattern pattern = Pattern.compile(
  "(\\d+)",
  Pattern.CASE_INSENSITIVE
);

String phrase = "I am 23";
Matcher match = pattern.matcher(phrase);
String result = match.find() ?
  match.group(1) : "";

System.out.println(result);

Regex Test

import java.util.regex.Matcher;
import java.util.regex.Pattern;

Pattern pattern = Pattern.compile(
  "Lee",
  Pattern.CASE_INSENSITIVE
);

String phrase = "Bob Lee";
Matcher match = pattern.matcher(phrase);
boolean result = match.find();

System.out.println(result);

Regex Characters

import java.util.regex.Matcher;
import java.util.regex.Pattern;

Pattern pattern = Pattern.compile(
  "(#+\\w?)",
  Pattern.CASE_INSENSITIVE
);

String phrase = "##I am legend##";
Matcher match = pattern.matcher(phrase);
String result = match.find() ?
  match.group(1) : "";

System.out.println(result);

IronCodeMan

Basics

Data Structure

Iterables

Classes

Regex

Concepts for Java

Print Text

Comments

Variables

Data Types

Math Op

Math Functions

If/Else

Ternary

Switch

Functions

Interpolation

Type Casting

Date and Time

Classes

Inheritance

Method Overload

Abstract Class

Static Class

Arrays/Lists

Array Methods

Concatenation

Sort Method

Objects

Maps (Key/Value)

Sets

Stack

Queues

Linked List

Graphs

For Loops

While Loops

Loop Breaks

Recursion

Regex Words

Regex Numbers

Regex Test

Regex Characters