Java basic intro Cheat Sheet by phon

public class MyDate {
	private int year;
	private int month;
	private int day;
	private int objectNumber;
	static int objectCounter;
	static String[] strMonths = { "January", "February",
			"March", "April", "May", "June", "July", "August", "September", "October", "November",
			"December"};
	MyDate(){
		this.setDate(1900,1,1);
		objectCounter++;
		objectNumber = objectCounter;
	}
	MyDate(int aYear,int aMonth,int aDay){
		this.setDate(aYear, aMonth, aDay);
		objectCounter++;
		objectNumber = objectCounter;
	}
	
	public int getObjectNumber() {
		return objectNumber;
	}
	public void setDate(int aYear,int aMonth,int aDay) {
		this.setYear(aYear);
		this.setMonth(aMonth);
		this.setDay(aDay);
	}
	public void setYear(int aYear) {
		year = aYear;
	}
	public void setMonth(int aMonth) {
		month = aMonth;
	}
	public void setDay(int aDay) {
		day = aDay;
	}
	public int getYear() {
		return year;
	}
	public int getMonth() {
		return month;
	}
	public int getDay() {
		return day;
	}
	public static int yearDiff (MyDate start, MyDate end) {
		int amonth = start.month;
		int ayear = start.year;
		int counter = 0;
		int result = 0;
		if (end.year >= start.year) {
				boolean process = true;
				while(process == true) {
					if(amonth == 12) {
						amonth = 1;
						ayear++;
						counter++;
					}
					else if (amonth == end.month && ayear == end.year) {
						process = false;
					}
					else {
						amonth++;
						counter++;
					}
				}
				if (start.day > end.day) {
					counter--;
				}
				result = counter / 12;
		}
		else {
			result = -1;
		}
		return result;
	}

	@Override
	public String toString() {
		return day +" "+ strMonths[month - 1] +" "+ year;
	}
	
	MyDate nextDay() {
		if (this.getMonth() == 12) {
			this.setDate(this.getYear() + 1,1,1);
		}
		else {
			if(this.getMonth() == 4 || this.getMonth() == 6 || this.getMonth() == 9 || this.getMonth() == 11) {
				if(this.getDay() == 30) {
					this.setMonth(this.getMonth() + 1);
					this.setDay(1);
				}
				else {
					this.setDay(this.getDay() + 1);
				}
			}
			else if(this.getMonth() != 2){
				if(this.getDay() == 31) {
					this.setDay(1);
					this.setMonth(this.getMonth() + 1);
				}
				else {
					this.setDay(this.getDay() + 1);
				}
			}
			else {
				if (isLeapYear(this.getYear()) == true && this.getDay() == 29) {
					this.setMonth(this.getMonth() + 1);
					this.setDay(1);
				}
				else if (isLeapYear(this.getYear()) == false && this.getDay() == 28) {
					this.setMonth(this.getMonth() + 1);
					this.setDay(1);
				}
				else {
					this.setDay(this.getDay() + 1);
				}
			}
		}
		return this;
	}
	
	MyDate nextMonth(){
		if (this.getMonth() == 12) {
			this.setMonth(1);
			this.setYear(this.getYear() + 1);
		}
		else if (this.getMonth() == 3 || this.getMonth() == 5 || this.getMonth() == 8 || this.getMonth() == 10) {
			if(this.getDay() == 31) {
				this.setDate(this.getYear(), this.getMonth() + 1, 30);
			}
			else {
				this.setMonth(this.getMonth() + 1);
			}
		}
		else if (this.getMonth() == 1){
			if (isLeapYear(this.getYear()) == true && this.getDay() >= 29) {
				this.setDate(this.getYear(),this.getMonth() + 1, 29);
			}
			else {
				this.setDate(this.getYear(),this.getMonth() + 1, 28);
			}
		}
		else{
			this.setMonth(this.getMonth() + 1);
		}
		return this;
	}
	
	MyDate nextYear() {
		if (isLeapYear(this.getYear()) == true && this.getDay() == 29 && this.getMonth() == 2) {
			this.setDate(this.getYear() + 1, 2 , 28);
		}
		else {
			this.setYear(this.getYear() + 1);			
		}
		return this;
	}
	MyDate previousDay() {
		if (this.getMonth() == 1 && this.getDay() == 1) {
			this.setYear(this.getYear() - 1);
			this.setMonth(12);
			this.setDay(31);
		}
		else {
			if(this.getMonth() == 5 || this.getMonth() == 7 || this.getMonth() == 10 || this.getMonth() == 12) {
				if (this.getDay() == 1) {
					this.setMonth(this.getMonth() - 1);
					this.setDay(30);
				}
				else {
					this.setDay(this.getDay() - 1);
				}
			}
			else if (this.getMonth() != 3) {
				if (this.getDay() == 1) {
					this.setDate(this.getYear(), this.getMonth() - 1, 31);
				}
				else {
					this.setDay(this.getDay() - 1);
				}
			}
			else {
				if(isLeapYear(this.getYear()) == true && this.getDay() == 1){
					this.setDate(this.getYear(),this.getMonth() - 1, 29);
				}
				else if (this.getDay() == 1) {
					this.setDate(this.getYear(), this.getMonth() - 1, 28);
				}
				else {
					this.setDay(this.getDay() - 1);
				}
			}
		}
		return this;
	}
	
	MyDate previousMonth() {
		if (this.getMonth() == 1) {
			this.setMonth(12);
			this.setYear(this.getYear() - 1);
		}
		else if (this.getMonth() == 5 || this.getMonth() == 7 || this.getMonth() == 10 || this.getMonth() == 12) {
			if(this.getDay() == 31) {
				this.setDate(this.getYear(), this.getMonth() - 1, 30);
			}
			else {
				this.setMonth(this.getMonth() - 1);
			}
		}
		else if (this.getMonth() == 3){
			if (isLeapYear(this.getYear()) == true && this.getDay() >= 29) {
				this.setDate(this.getYear(),this.getMonth() - 1, 29);
			}
			else {
				this.setDate(this.getYear(),this.getMonth() - 1, 28);
			}
		}
		else{
			this.setMonth(this.getMonth() - 1);
		}
		return this;
	}
	
	MyDate previousYear() {
		if (isLeapYear(this.getYear()) == true && this.getDay() == 29 && this.getMonth() == 2) {
			this.setDate(this.getYear() - 1, 2 , 28);
		}
		else {
			this.setYear(this.getYear() -1);			
		}
		return this;	
	}
	static boolean isLeapYear(int Year) {
		if (Year % 4 != 0) {
			return false;
		}
		else if (Year % 100 != 0) {
			return true;
		}
		else if (Year % 400 != 0) {
			return false;
		}
		else {
			return true;
		}
	}
}

import java.time.LocalDate;

public class Person {
	private String firstname;
	private String lastname;
	private MyDate birthday = new MyDate();
	
	Person(String aFirstname, String aLastname){
		firstname = aFirstname;
		lastname = aLastname;
	}
	
	Person(String aFirstname, String aLastname, int aYear, int aMonth, int aDay){
		firstname = aFirstname;
		lastname = aLastname;
		birthday.setDate(aYear, aMonth, aDay);
	}
	public int getAge(MyDate aDate) {
		int age = MyDate.yearDiff(birthday, aDate);
		return age;
	}
	public boolean isEligible(MyDate elecDate) {
		if (MyDate.yearDiff(this.birthday, elecDate) >= 18) {
			return true;
		}
		else {
			return false;
		}
	}
	public void printPersonInfo() {
		System.out.println("Person: "+firstname+" "+lastname);
		System.out.println("Birthday: "+birthday.getDay()+" "+MyDate.strMonths[birthday.getMonth() - 1]+" "+birthday.getYear());
	}

}

import java.util.Scanner;
public class ElectionTester {
	public static void main(String[] args) {
		MyDate election = new MyDate(2019, 3, 24);		
		Person a = new Person("Lalisa", "Manoban", 1997, 3, 27);
		printPersonElectionInfo(a, election);	
		Person b = new Person("Nuda", "Inter", 2012, 1, 16);
		printPersonElectionInfo(b, election);			
		Person c = new Person("Hallo", "World",1998,2,1);
		printPersonElectionInfo(c, election);	//
		boolean processing = true;
		while(processing == true) {
			String firstname;
			String lastname;
			int year;
			int month;
			int day;
			Scanner in = new Scanner(System.in);
			System.out.print("Enter firstname or type 'q' to exit:");
			String dataA = in.nextLine();
			if(dataA.equals("q") == true) {
				processing = false;
				break;
			}
			else {
				firstname = dataA;
				Scanner in1 = new Scanner(System.in);
				System.out.print("Enter lastname:");
				lastname = in1.nextLine();
				Scanner in3 = new Scanner(System.in);
				System.out.print("Enter year of birthday: ");
				year = in3.nextInt();
				Scanner in4 = new Scanner(System.in);
				System.out.print("Enter month of birthday: ");
				month = in4.nextInt();
				Scanner in5 = new Scanner(System.in);
				System.out.print("Enter day of birthday: ");
				day = in5.nextInt();
				Person data = new Person(firstname,lastname,year,month,day);
				printPersonElectionInfo(data, election);
			}
		}
		System.out.println("Exit the program. Thank you.");
	}
	public static void printPersonElectionInfo(Person p, MyDate election) {
		p.printPersonInfo();
		System.out.println("Age: " + p.getAge(election));
		if(p.isEligible(election))
			System.out.println("This person is eligible to vote.");
		else
			System.out.println("This person is NOT eligible to vote");
		
		System.out.println("-----------------------------------");
	}
}