Introduction to Java class and objects/function/final

These are general Java programming tutorials provided for free on YouTube:
http://thenewboston.org/list.php?cat=31

Java Syntax

I would personally watch as many as I could until I feel comfortable with Java. Once you get comfortable with Java, you can start Android programming:
http://thenewboston.org/list.php?cat=6

I am visual so I like learning by watching videos. If you would like to read instead, there are many other websites. For example: http://docs.oracle.com/javase/tutorial/


filenames must end with .java

	javac classname.java

	java classname

	error: Class names, 'variables.txt', are only accepted if annotation processing is explici
	tly requested
	1 error

	C:\JAVA>

	When they compile, the output file is .class and the filename corresponds with the class name in the file.


	**Make sure your class is named properaly (class java ...)


+ concatenation operator

	public class

		public method


	dot seperator

		class.method(aurgument );

			public class tuna {
				public void simpleMessage() {
					System.out.println("This is another class");
				}
			}

			public class apples {
				public static void main(String[] args) {
					tuna tunaObject = new tuna();
					tunaObject.simpleMessage();
				}
			}


	System.out.printf("Your first gf was %s", getName());
	System.out.println //prints endline breaks
		System.out.print(tuna); //continues from the previous

		public class tuna {
			public void simpleMessage(String name) {
				System.out.println("Hello " + name);
			}
		}


if/else statments

if (argument)
	dothis...;
else if (argument)
	dothat...;
...
else
	doother...;

Nesting
if () {
	if () {
		...
	}
}


Average

import java.util.Scanner;

class apples {

	public static void main(String[] args) {

		Scanner input = new Scanner(System.in);

		int total = 0;
		int grade;
		int average;
		int counter = 0;

		while (counter < 10) {

			grade = input.nextInt();
			total = total + grade;
			counter++;

		}

		average = total/10;
		System.out.println("Your average is " + average);

	}

}


Arrays

		int bucky[] = new int[10];

		int bucky[] = {2,4,5,7,9}; array initializer (subscript/indexer)

		bucky[0]=87;
		bucky[1]=543;
		bucky[9]=65;

		System.out.println(bucky[1]);


		Index

			System.out.println("Index\tValue");

			int bucky[] = {32, 48, 18, 54, 2};

			for(int counter=0; counter < bucky.length; counter++) {

				System.out.println(counter + "\t" + bucky[counter]);

			}


		Total Sum

		int bucky[] = {21, 16, 86, 21, 3};
		int sum=0;

		for (int counter=0; counter<bucky.length; counter++) {

			sum+=bucky[counter];

		}

		System.out.println("The sum of these numbers is " + sum);



Conditional Operators


System.out.println(age > 50 ? "You are old" : "You are Young");


import java.util.Scanner;

	public class apples {
		public static void main(String[] args) {

			Scanner input = new Scanner(System.in);
			tuna tunaObject = new tuna();

			System.out.println("Enter your name here: ");
			String name = input.nextLine();

			tunaObject.simpleMessage(name);

		}
	}



toString

	class apples {
		public static void main(String[] args) {
			potpie potObject = new potpie(4,5,6);
		}
	}

	public class potpie {
		private int month;
		private int day;
		private int year;

		public potpie(int m, int d, int y) {
			month = m;
			day = d;
			year = y;
			System.out.printf("The constructor for this is %s\n", this);
		}

		public String toString() {
			return String.format("%d/%d/%d", month, day, year);
		}

	}


Composition


	class apples {

		public static void main(String[] args) {

			potpie potObject = new potpie(4,5,6);
			tuna tunaObject = new tuna("Greg", potObject);

			System.out.println(tunaObject);

		}

	}


	public class tuna {

		private String name;
		private potpie birthday;

		public tuna(String theName, potpie theDate) {

			name = theName;
			birthday = theDate;

		}

		public String toString() {

			return String.format("My name is %s, my birthday is %s", name, birthday);

		}

	}

	public class potpie {

		private int month;
		private int day;
		private int year;

		public potpie(int m, int d, int y) {

			month = m;
			day = d;
			year = y;

			System.out.printf("The constructor for this is %s\n", this);

		}

		public String toString() {

			return String.format("%d/%d/%d", month, day, year);

		}

	}


Type-safe enumerations (enum types)

	JDK 1.5 is not available, type-safe enumerations can still be implemented as a regular Java class
Enumeration

	class apples {

		public static void main(String[] args) {

			for (tuna people: tuna.values())

			System.out.printf("%s\t%s\t%s\n", people, people.getDesc(), people.getYear());

		}

	}

	public enum tuna {

		bucky("nice", "22"),
		kelsey("cutie", "10"),
		julia("bigmistake", "12");

		private final String desc;
		private final String year;

		tuna(String description, String birthday) {
			desc = description;
			year = birthday;

		}

		public String getDesc() {
			return desc;
		}

		public String getYear() {
			return year;
		}

	}



	EnumSet Range

		import java.util.EnumSet;

		class apples {

			public static void main(String[] args) {
				for (tuna people: tuna.values())
					System.out.printf("%s\t%s\t%s\n", people, people.getDesc(), people.getYear());

				System.out.println("\nAnd for the range of constants!!!\n");

				for (tuna people: EnumSet.range(tuna.kelsey, tuna.candy))
					System.out.printf("%s\t%s\t%s\n", people, people.getDesc(), people.getYear());
			}

		}


		public enum tuna {

			bucky("nice", "22"),
			kelsey("cutie", "10"),
			julia("bigmistake", "12"),
			nicole("italian", "13"),
			candy("different", "14"),
			erin("I wish", "16");

			private final String desc;
			private final String year;

			tuna(String description, String birthday) {
				desc = description;
				year = birthday;

			}

			public String getDesc() {
				return desc;
			}

			public String getYear() {
				return year;
			}
		}


Static

	Are defined the same the whole time the program is run, and can be accessed globally, using the class name reference.

	class apples {
		public static void main(String[] args) {
			tuna member1 = new tuna("Meagan", "Fox");
			tuna member2 = new tuna("Natalie", "Portman");
			tuna member3 = new tuna("Taylor", "Swift");

			System.out.println();
			System.out.println(member2.getFirst());
			System.out.println(member2.getLast());
			System.out.println(member2.getMembers());
			System.out.println();

			System.out.println(tuna.getMembers());
		}

	}

	public class tuna {

		private String first;
		private String last;
		private static int members = 0;

		public tuna(String fn, String ln) {

			first = fn;
			last = ln;
			members++;
			System.out.printf("Constructor for %s %s, members in the club: %d\n", first, last, members);

		}


		public String getFirst () {
			return first;
		}

		public String getLast () {
			return last;
		}

		public static int getMembers() {
			return members;
		}

	}


Final

	class apples {
		public static void main(String[] args) {
			tuna tunaObject = new tuna(10);

			for(int i = 0; i < 5; i++) {
				tunaObject.add();
				System.out.printf("%s", tunaObject);
			}
		}
	}

	public class tuna {

		private int sum;
		private final int NUMBER; //(final) initializer ( = 2; )

		public tuna(int x) {
			NUMBER = x;
		}

		public void add() {
			sum+=NUMBER;
		}

		public String toString() {
			return String.format("sum = %d\n", sum);
		}

	}



Building Objects for Constructors

	Variable length arguments

	class apples {
		public static void main(String[] args) {
			//tuna tunaObject = new tuna();
			//System.out.println(tunaObject.toMilitary());
			//System.out.println(tunaObject.toString());

			//tunaObject.setTime(13, 27, 6);
			//System.out.println(tunaObject.toMilitary());
			//System.out.println(tunaObject.toString());


			tuna tunaObject = new tuna();
			tuna tunaObject2 = new tuna(5);
			tuna tunaObject3 = new tuna(5,13);
			tuna tunaObject4 = new tuna(5,13,43);

			System.out.printf("%s\n", tunaObject.toMilitary());
			System.out.printf("%s\n", tunaObject2.toMilitary());
			System.out.printf("%s\n", tunaObject3.toMilitary());
			System.out.printf("%s\n", tunaObject4.toMilitary());

		}

	}



	public class tuna {

		private int hour;
		private int minute;
		private int second;

		public tuna() {
			this(0,0,0);
		}

		public tuna(int h) {
			this(h,0,0);
		}

		public tuna(int h, int m) {
			this(h,m,0);
		}

		public tuna(int h, int m, int s) {
			setTime(h,m,s);
		}

		public void setTime(int h, int m, int s) {
			setHour(h);
			setMinute(m);
			setSecond(s);
		}

		public void setHour (int h) {
			hour = ((h >=0 && h < 24) ? h : 0);
		}

		public void setMinute (int m) {
			minute = ((m >=0 && m < 60) ? m : 0);
		}

		public void setSecond (int s) {
			second = ((s >=0 && s < 60) ? s : 0);
		}

		public int getHour () {
			return hour;
		}

		public int getMinute () {
			return minute;
		}

		public int getSecond () {
			return second;
		}

		public String toMilitary() {
			return String.format("%02d:%02d:%02d", getHour(), getMinute(), getSecond());
		}
	}


Inheritance (Extends)

	Can be used on multiple levels (hierarchical) with inheritance

		only public methods can be inherited.

		tuna extends potpie
			potpie extends food

	class apples {
		public static void main(String[] args) {
			tuna tunaObject = new tuna();
			potpie potObject = new potpie();

			tunaObject.eat();
			potObject.eat();
		}
	}

	public class tuna extends food {
		public void eat() {
			System.out.println("I am the new method of tuna");
		}
	}

	public class potpie extends food {

	}

	public class food {
		public void eat() {
			System.out.println("I am the eat methods");
		}
	}






Constructor

	method must match the same name (method name) as the class name, inorder for it to be considered a constructor


Math Operators

	++pre-increment variable (-- subtraction)

		increments the variable before it returns


	post-increment++ variable (-- subtraction)

		increments the variable after it returns


		increment assign operator

			variable += 5


	Logical Operator (Multiple Test)

		&&	AND
		||	OR

			var1 && var2 (both have to be true)
			var1 || var2 (either must be true, the other maybe false)


	int whole numbers

		int + int = sum
		int * int = product
		int / int = divide
		int % int = modulus (remainder)

		int var = 1;

		int var_name(, var_name2, var_name3...);

			var_name = 1;


	double

		fraction/decimal numbers


	String variable = "value";



	"...it can only do one or the other."

	if (condition) {
		//condition is true
		testing

		!=		does not equal
		===		absolute equal
		>=		greater than or equal to
		<=		less than or equal to
		>		greater than
		<		less than

		block

	} else {
		//condition is false
	}

	While Loop

	while (counter < 10) {
		System.out.println(counter);
		counter++;
	}


	Do-while loop

		int counter = 0;

	do {

		System.out.println(counter);
		counter++;

	} while (counter <= 10);


Java Methods (declare after being used?)

	public static void main(String[] args) {
		int bucky[]={3,4,5,6,7};
		change(bucky);
		for(int y:bucky)
			System.out.println(y);
	}

	public static void change(int x[]) {
		for (int counter = 0; counter < x.length; counter++ ) {
			x[counter] += 5;
		}
	}

Java Local Variables

	public void setTime(int hour, int minute, int second) {
		this.hour = 4;
		this.minute = 5;
		this.second = 6;
	}


Java Global Variables

	public int hour = 1;
	public int minute = 2;
	public int second = 3'


Java Multi-Array

		int firstarray[][]={{8,9,10,11}, {12, 13, 14, 15}};
		int secondarray[][]={{30,31,32,33},{43},{4,5,6}};

		firstarray[0][1]; //[col][row]


Java Multi-Array Display

	public static void main(String[] args) {

		int firstarray[][]={{8,9,10,11}, {12, 13, 14, 15}};
		int secondarray[][]={{30,31,32,33},{43},{4,5,6}};

		//firstarray[0][1]; //[col][row]

		System.out.println("This is the first array");
		display(firstarray);

		System.out.println("This is the second array");
		display(secondarray);

	}

	public static void display(int x[][]) {

		for (int row=0; row < x.length; row++) {
			for (int column=0; column < x[row].length; column++ ) {
				System.out.print(x[row][column]+"\t");
			}
			System.out.println();
		}

	}


Variable Length Arguments

	public static void main(String[] args) {

		System.out.println(average(43,6,26,23));

	}

	public static int average(int...numbers) {

		int total = 0;

		for (int x:numbers)
			total+=x;

		return total/numbers.length;

	}



For loop

for(int counter = 1; counter <= 10; counter++) //counter+=3 step by 3, 6, 9...

Enhanced For Loop

		int bucky[] = {3,4,5,6,7};
		int total = 0;

		for (int x: bucky) { total +=x; }

		System.out.println(total);



Random Dice

	import java.util.Random;

		Random dice = new Random();
		int number;

		for(int counter=1; counter <= 10; counter++) {

			number = 1+dice.nextInt(6);

			System.out.println(number + " ");

		}


Random Face/Dice Generator

	Random rand = new Random();

		int freq[] = new int[7];

		for (int roll = 1; roll < 1000; roll++ ) {

			++freq[1+rand.nextInt(6)];

		}

		System.out.println("Face\tFrequency");

		for (int face=1; face<freq.length; face++) {

			System.out.println(face+"\t"+freq[face]);

		}


Time

	private int hour;
	private int minute;
	private int second;

	public void setTime(int h, int m, int s) {
		hour = ((h >= 0 && h < 24) ? h : 0);
		minute = ((m >= 0 && m < 60) ? m : 0);
		second = ((s >= 0 && s < 60) ? s : 0);
	}

	public String toMilitary() {

		return String.format("%02d:%02d:%02d", hour, minute, second );

	}

	public String toString() {

		return String.format("%d:%02d:%02d %s", ((hour==0 || hour==12) ? 12 : hour%12), minute, second, (hour < 12 ? "AM" : "PM"));

	}


	public static void main(String[] args) {
		tuna tunaObject = new tuna();
		System.out.println(tunaObject.toMilitary());
		tunaObject.setTime(13, 27, 6);
		System.out.println(tunaObject.toMilitary());
	}


Compound Interest

	A=P(1+R)^n

	A = Amount
	P = Principle
	* (1+R = Rate) ^ (power) n = Years

	double amount;
	double principal = 10000;
	double rate = .01;

	for (int day = 1; day <= 20; day++) {

		amount = principal*Math.pow(1 + rate, day);
		System.out.println(day + "   " + amount);

	}

System.out.println(Math.abs());

abs = absolute value (-26.7 == 26.7)
ceil = ceiling (7.4 == 8.0)
floor = floor (7.8 == 7.0)
max = maximum (8.6, 5.2 == 8.6)
min = minimum (8.6, 5.2 == 5.2)
pow = power (5, 3 == 125)
sqrt = square root (9 == 3)


GUI

	import javax.swing.JOptionPane;

	class apples {
		public static void main(String[] args) {

			String fn = JOptionPane.showInputDialog("Enter first number");
			String sn = JOptionPane.showInputDialog("Enter second number");

			int num1 = Integer.parseInt(fn);
			int num2 = Integer.parseInt(sn);
			int sum = num1 + num2;

			JOptionPane.showMessageDialog(null, "The answer is " +sum, "the title", JOptionPane.PLAIN_MESSAGE);
		}
	}


GUI with JFrame

	import javax.swing.JFrame;

	class apples {
		public static void main(String[] args) {

			tuna bucky = new tuna();
			bucky.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
			bucky.setSize(275,180);
			bucky.setVisible(true);

		}
	}

	import java.awt.FlowLayout;
	import javax.swing.JFrame;
	import javax.swing.JLabel;

	public class tuna extends JFrame {
		private JLabel item1;
		public tuna() {
			super("The Title Bar");
			setLayout(new FlowLayout());

			item1 = new JLabel("This is a sentence");
			item1.setToolTipText("This is going to show up on hover.");
			add(item1);
		}
	}



Event Handling

	import javax.swing.JFrame;

	class apples {
		public static void main(String[] args) {
			tuna bucky = new tuna();
			bucky.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
			bucky.setSize(350,100);
			bucky.setVisible(true);
		}
	}

	import java.awt.FlowLayout;
	import java.awt.event.ActionListener;
	import java.awt.event.ActionEvent;
	import javax.swing.JFrame;
	import javax.swing.JTextField;
	import javax.swing.JPasswordField;
	import javax.swing.JOptionPane;

	public class tuna extends JFrame {

		private JTextField item1;
		private JTextField item2;
		private JTextField item3;
		private JPasswordField passwordField;

		public tuna() {

			super("The Title Bar");
			setLayout(new FlowLayout());

			item1 = new JTextField(10);
			add(item1);

			item2 = new JTextField("Enter text here");
			add(item1);

			item3 = new JTextField("uneditable", 20);
			item3.setEditable(false);
			add(item3);

			passwordField = new JPasswordField("mypass");
			add(passwordField);

			thehandler handler = new thehandler();
			item1.addActionListener(handler);
			item2.addActionListener(handler);
			item3.addActionListener(handler);
			passwordField.addActionListener(handler);

		}

		private class thehandler implements ActionListener {

			public void actionPerformed(ActionEvent event) {

				String string = "";

				if (event.getSource() == item1)
					string = String.format("field 1: %s", event.getActionCommand());
				else if(event.getSource() == item2)
					string = String.format("field 2: %s", event.getActionCommand());
				else if(event.getSource() == item3)
					string = String.format("field 3: %s", event.getActionCommand());
				else if(event.getSource() == passwordField)
					string = String.format("password field is : %s", event.getActionCommand());

				JOptionPane.showMessageDialog(null, string);

			}

		}

	}