Java
Variables
These store data for processing.
A variable is given a data type and a name (or identifier).
A data type tells the system what kind of data it should store and a name or an identifier is set by a programmer to uniquely reference a specific data.
See sample code below:
String name = "Bob";
int age = 18;
double grade = 85.25;
char gradeLetter = 'B';
boolean isOnline = false;
String
Strings store a sequence of characters and are enclosed in double quotes.
See sample code below:
String name = "Bob";
Integer
Integers store whole numbers.
The max value you can store in an integer is 2147483647.
See sample code below:
int age = 18;
Double
Doubles store floating-point numbers (or numbers with decimal values).
The max value you can store in a double is approximately 1.7976931348623157 x 10308.
See sample code below:
double grade = 85.25;
Character
Characters store single alphanumeric characters and are enclosed in single quotes.
See sample code below:
char gradeLetter = 'B';
Boolean
Booleans only store two (2) possible values: true or false.
See sample code below:
boolean isOnline = false;
Operators
Every programming language provides a set of operators to use in manipulating variables.
Math Operators
See sample code below:
int a = 6;
int b = 5;
int sum = a + b;
int difference = a - b;
int product = a * b;
int quotient = a / b;
int remainder = a % b;
Addition
The plus sign (+) is used to add two numbers.
See sample code below:
int a = 6;
int b = 5;
int sum = a + b;
Subtraction
The dash sign (-) is used to subtract two numbers.
See sample code below:
int a = 6;
int b = 5;
int difference = a - b;
Multiplication
The asterisk sign (*) is used to multiply two numbers.
See sample code below:
int a = 6;
int b = 5;
int product = a * b;
Division
The forward slash sign (/) is used to divide two numbers.
See sample code below:
int a = 6;
int b = 5;
int quotient = a / b;
Modulo
The percent sign (%) is used to divide two numbers and returns the remainder.
See sample code below:
int a = 6;
int b = 5;
int remainder = a % b;
Increment
The double plus sign (++) is used to increase the value of a number by one (1).
See sample code below:
int a = 6;
a++;
Decrement
The double dash sign (--) is used to decrease the value of a number by one (1).
See sample code below:
int a = 6;
a--;
Assignment Operators
See sample code below:
int a = 6;
a += 5;
a -= 5;
a *= 5;
a /= 5;
Assignment
The equal sign (=) is used to assign a value to a variable.
See sample code below:
int a = 6;
Addition and Assignment
The plus and equal sign (+=) is used to add a value to a variable with the same data type and assign it to itself.
See sample code below:
int a = 6;
a += 5;
Subtraction and Assignment
The dash and equal sign (-=) is used to subtract a value to a variable with the same data type and assign it to itself.
See sample code below:
int a = 6;
a -= 5;
Multiplication and Assignment
The asterisk and equal sign (*=) is used to multiply a value to a variable with the same data type and assign it to itself.
See sample code below:
int a = 6;
a *= 5;
Division and Assignment
The forward slash and equal sign (/=) is used to divide a value to a variable with the same data type and assign it to itself.
See sample code below:
int a = 6;
a /= 5;
Conditional Operators
These operators always returns a boolean value.
See sample code below:
boolean a = 6 == 5;
boolean b = 6 != 5;
boolean c = 6 < 5;
boolean d = 6 > 5;
boolean e = 6 <= 5;
boolean f = 6 >= 5;
Equal to
The double equal sign (==) is used to compare two values together and check if the left variable is equal to the right variable.
See sample code below:
boolean a = 6 == 5;
Not equal to
The exclamation point and equal sign (!=) is used to compare two values together and check if the left variable is not equal to the right variable.
See sample code below:
boolean a = 6 != 5;
Less than
The left bracket symbol (<) is used to compare two values together and check if the left variable is less than the right variable.
See sample code below:
boolean a = 6 < 5;
Greater than
The right bracket symbol (>) is used to compare two values together and check if the left variable is greater than the right variable.
See sample code below:
boolean a = 6 > 5;
Less than or equal to
The left bracket symbol and equal sign (<=) is used to compare two values together and check if the left variable is less than or equal to the right variable.
See sample code below:
boolean a = 6 <= 5;
Greater than or equal to
The right bracket symbol and equal sign (>=) is used to compare two values together and check if the left variable is greater than or equal to the right variable.
See sample code below:
boolean a = 6 >= 5;
Logical Operators
These operators always returns a boolean value.
See sample code below:
boolean a = true && false;
boolean b = true || false;
boolean c = !true;
And
The double ampersand symbol (&&) is used to combine multiple conditions.
If both values are true, then the result is true.
If one value is false, then the result is false.
See sample code below:
boolean a = true && false;
Or
The double pipe symbol (||) is used to combine multiple conditions.
If one value is true, then the result is true.
See sample code below:
boolean a = true || false;
Not
The exclamation point (!) is used to reverse a condition.
If a condition is true, then the result is false.
If a condition is false, then the result is true.
See sample code below:
boolean a = !true;
Basics
Learning a programming language usually starts with using the console.
What you need to know
Creating simple programs in Java starts with putting code inside its main loop function.
See sample code below:
class ConsoleApp1 {
public static void main(String[] args){
// your code here
}
}
Comments
Comments are specific texts in a programming language that is ignored in a program's execution.
See sample code below:
// single-line comment
/*
* multi-line comment
*/
Output
See sample code below:
System.out.println("Sample text");
Input
Java uses the Scanner package to get input from the console.
The Scanner package is imported by calling import java.util.Scanner; at the top of your class.
See sample code below:
import java.util.Scanner;
class ConsoleApp1 {
public static void main(String[] args){
Scanner scanner = new Scanner(System.in);
String a = scanner.nextLine();
}
}
Conditional Statements
Conditional statements make use of the keywords if, else, and else if.
The keyword if is always followed by a condition enclosed in parentheses.
If the condition inside the parentheses is true, it will then execute the code it contains.
Else, it will then execute the code inside the else block.
The else if keyword simply combines both the if and else statement.
See sample code below:
if (6 == 5){
// your code here
} else if (6 < 5){
// your code here
} else {
// your code here
}
Looping Statements
Looping statements make use of the keywords for, while, and do.
While
The keyword while is always followed by a condition enclosed in parentheses.
See sample code below:
while (6 != 5){
// your code here
}
For
The keyword for is also followed by a statement enclosed in parentheses but requires three (3) statements inside the parentheses: initialization, condition, and update.
See sample code below:
for (int a = 0; a < 6; a++){
// your code here
}
Do...While
The keyword do acts the same as a while statment and is always accompanied by the while statement.
The only difference being: do...while statements executes the code inside it first before checking the condition; and the while statements checks for the condition first before executing.
See sample code below:
do {
// your code here
} while (6 != 5);
C#
Variables
These store data for processing.
A variable is given a data type and a name (or identifier).
A data type tells the system what kind of data it should store and a name or an identifier is set by a programmer to uniquely reference a specific data.
See sample code below:
string name = "Bob";
int age = 18;
double grade = 85.25;
char gradeLetter = 'B';
bool isOnline = false;
String
Strings store a sequence of characters and are enclosed in double quotes.
See sample code below:
string name = "Bob";
Integer
Integers store whole numbers.
The max value you can store in an integer is 2147483647.
See sample code below:
int age = 18;
Double
Doubles store floating-point numbers (or numbers with decimal values).
The max value you can store in a double is approximately 1.7976931348623157 x 10308.
See sample code below:
double grade = 85.25;
Character
Characters store single alphanumeric characters and are enclosed in single quotes.
See sample code below:
char gradeLetter = 'B';
Bool
Bools only store two (2) possible values: true or false.
See sample code below:
bool isOnline = false;
Operators
Every programming language provides a set of operators to use in manipulating variables.
Math Operators
See sample code below:
int a = 6;
int b = 5;
int sum = a + b;
int difference = a - b;
int product = a * b;
int quotient = a / b;
int remainder = a % b;
Addition
The plus sign (+) is used to add two numbers.
See sample code below:
int a = 6;
int b = 5;
int sum = a + b;
Subtraction
The dash sign (-) is used to subtract two numbers.
See sample code below:
int a = 6;
int b = 5;
int difference = a - b;
Multiplication
The asterisk sign (*) is used to multiply two numbers.
See sample code below:
int a = 6;
int b = 5;
int product = a * b;
Division
The forward slash sign (/) is used to divide two numbers.
See sample code below:
int a = 6;
int b = 5;
int quotient = a / b;
Modulo
The percent sign (%) is used to divide two numbers and returns the remainder.
See sample code below:
int a = 6;
int b = 5;
int remainder = a % b;
Increment
The double plus sign (++) is used to increase the value of a number by one (1).
See sample code below:
int a = 6;
a++;
Decrement
The double dash sign (--) is used to decrease the value of a number by one (1).
See sample code below:
int a = 6;
a--;
Assignment Operators
See sample code below:
int a = 6;
a += 5;
a -= 5;
a *= 5;
a /= 5;
Assignment
The equal sign (=) is used to assign a value to a variable.
See sample code below:
int a = 6;
Addition and Assignment
The plus and equal sign (+=) is used to add a value to a variable with the same data type and assign it to itself.
See sample code below:
int a = 6;
a += 5;
Subtraction and Assignment
The dash and equal sign (-=) is used to subtract a value to a variable with the same data type and assign it to itself.
See sample code below:
int a = 6;
a -= 5;
Multiplication and Assignment
The asterisk and equal sign (*=) is used to multiply a value to a variable with the same data type and assign it to itself.
See sample code below:
int a = 6;
a *= 5;
Division and Assignment
The forward slash and equal sign (/=) is used to divide a value to a variable with the same data type and assign it to itself.
See sample code below:
int a = 6;
a /= 5;
Conditional Operators
These operators always returns a bool value.
See sample code below:
bool a = 6 == 5;
bool b = 6 != 5;
bool c = 6 < 5;
bool d = 6 > 5;
bool e = 6 <= 5;
bool f = 6 >= 5;
Equal to
The double equal sign (==) is used to compare two values together and check if the left variable is equal to the right variable.
See sample code below:
bool a = 6 == 5;
Not equal to
The exclamation point and equal sign (!=) is used to compare two values together and check if the left variable is not equal to the right variable.
See sample code below:
bool a = 6 != 5;
Less than
The left bracket symbol (<) is used to compare two values together and check if the left variable is less than the right variable.
See sample code below:
bool a = 6 < 5;
Greater than
The right bracket symbol (>) is used to compare two values together and check if the left variable is greater than the right variable.
See sample code below:
bool a = 6 > 5;
Less than or equal to
The left bracket symbol and equal sign (<=) is used to compare two values together and check if the left variable is less than or equal to the right variable.
See sample code below:
bool a = 6 <= 5;
Greater than or equal to
The right bracket symbol and equal sign (>=) is used to compare two values together and check if the left variable is greater than or equal to the right variable.
See sample code below:
bool a = 6 >= 5;
Logical Operators
These operators always returns a bool value.
See sample code below:
bool a = true && false;
bool b = true || false;
bool c = !true;
And
The double ampersand symbol (&&) is used to combine multiple conditions.
If both values are true, then the result is true.
If one value is false, then the result is false.
See sample code below:
bool a = true && false;
Or
The double pipe symbol (||) is used to combine multiple conditions.
If one value is true, then the result is true.
See sample code below:
bool a = true || false;
Not
The exclamation point (!) is used to reverse a condition.
If a condition is true, then the result is false.
If a condition is false, then the result is true.
See sample code below:
bool a = !true;
Basics
Learning a programming language usually starts with using the console.
What you need to know
Creating simple programs in C# starts with putting code inside its main loop function.
See sample code below:
using System;
namespace ConsoleApp1
{
internal class Program
{
static void Main(string[] args)
{
// your code here
}
}
}
Comments
Comments are specific texts in a programming language that is ignored in a program's execution.
See sample code below:
// single-line comment
/*
* multi-line comment
*/
Output
See sample code below:
Console.WriteLine("Sample text");
Input
See sample code below:
string a = Console.ReadLine();
Conditional Statements
Conditional statements make use of the keywords if, else, and else if.
The keyword if is always followed by a condition enclosed in parentheses.
If the condition inside the parentheses is true, it will then execute the code it contains.
Else, it will then execute the code inside the else block.
The else if keyword simply combines both the if and else statement.
See sample code below:
if (6 == 5)
{
// your code here
}
else if (6 < 5)
{
// your code here
}
else
{
// your code here
}
Looping Statements
Looping statements make use of the keywords for, while, and do.
While
The keyword while is always followed by a condition enclosed in parentheses.
See sample code below:
while (6 != 5)
{
// your code here
}
For
The keyword for is also followed by a statement enclosed in parentheses but requires three (3) statements inside the parentheses: initialization, condition, and update.
See sample code below:
for (int a = 0; a < 6; a++)
{
// your code here
}
Do...While
The keyword do acts the same as a while statment and is always accompanied by the while statement.
The only difference being: do...while statements executes the code inside it first before checking the condition; and the while statements checks for the condition first before executing.
See sample code below:
do
{
// your code here
}
while (6 != 5);
Android (Java)
Basics
Programming in Android using Java starts with using the Android Studio IDE.
What you need to know
To start creating applications for Android, we first need to create a new project.
There will be a button available at the top of the starting page of Android Studio named "New Project".
Android Studio New Project Button
Creating a new project in Android Studio may be confusing for some people because of the multiple options given to us at the start.
Android Studio New Project Dialog
To keep things simple, we can start with the "Empty Views Activity" option
Android Studio Empty Views Option
Do note that other versions of Android Studio may not include this option.
For that scenario, we can simply pick the "No Activity" option.
Android Studio No Activity Option
After clicking next, we can then edit a few details of the project such as:
- The name
Android Studio Project Name
- The package name
Android Studio Project Package Name
- The save location of the project
Android Studio Project Save Location
- The programming language the project will use
Android Studio Project Programming Language
- The minimum Android version the project (or the application) support
Android Studio Project Android Version
- And the build configuration language of the project.
Android Studio Project Build Configuration Language
For now, we are going to be using these settings below:
Android Studio Project Settings
Upon clicking the "Finish" button, you will see this window pop up.
Android Studio IDE
Do note that you will need to let the IDE finish the Gradle project sync indicated near the top,
Android Studio Gradle Sync at the Top
and at the bottom of the window.
Android Studio Gradle Sync at the Bottom
After the Gradle has finished syncing, this will be the final look of the IDE.
Android Studio IDE Final Look
Do note that if you chose the "No Activity" option, you will not have the default "activity_main.xml" and "MainActivity.java" files at the start.
Android Studio No Activity IDE Final Look
To add a new activity, right-click on the "app" folder on the left and choose the "New > Activity > Empty Views Activity" option.
Android Studio No Activity New Activity
You can choose to either change or ignore the settings on the pop-up window.
Android Studio No Activity New Activity Settings
After clicking the "Finish" button, make sure to edit the "AndroidManifest.xml" located at the folders at the left at "app > manifests > AndroidManifest.xml" and modify the "<activity>" tag for the Activity you just created just like this example below.
Android Studio No Activity Manifest
This will serve as the default activity that will open as soon as your application starts.
Activity
Activities in Android represents a single screen in an application.
An example of this is the "MainActivity.java" that is generated at the start of a new project.
Android Studio Activity
Every activity is composed of two (2) things.
The corresponding Java and XML files.
Android Studio Activity Composition
The Java file contains the back-end functions of the activity.
Android Studio Activity Java
The XML file contains the front-end functions of the activity.
Android Studio Activity XML
Intent
An Intent represents an action you want an activity to do.
Intents can be used to start activities.
See sample code below:
Intent intent = new Intent(CurrentActivity.this, ActivityToStart.class);
startActivity(intent);
Intents can also be used to pass data to activities.
See sample code below:
Intent intent = new Intent(CurrentActivity.this, ActivityToStart.class);
intent.putExtra("data_name", "data_value");
startActivity(intent);
The data sent to the other activity using "putExtra()" can be retrieved using the "getIntent()" method.
See sample code below:
String data = getIntent().getStringExtra("data_name");
The method to be used in getting your data should match the type of the data you sent.
User Interface
The XML file of an activity is where the user interface lives.
Button
A button represents a clickable element.
See sample code below:
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Sample text"/>
The code above will look like the example below.
Android Studio Button
TextView
A TextView element shows text.
See sample code below:
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Sample text"/>
The code above will look like the example below.
Android Studio TextView
EditText
An EditText element gives a user an area to type in.
See sample code below:
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:hint="Sample text"/>
A hint acts as a placeholder to give a user some context about an element.
The code above will look like the example below.
Android Studio EditText
Intermediate
This section will talk about a few functions available in Android.
Getting text from a widget
Getting any text or content from any widget, such as TextViews and EditTexts, is very simple.
See sample code below:
EditText editText = findViewById(R.id.editTextId);
String text = editText.getText().toString();
Alerting a user through an EditText
An EditText contains a "setError()" method to alert a user about an input.
See sample code below:
EditText editText = findViewById(R.id.editTextId);
editText.setOnKeyListener(new View.OnKeyListener() {
@Override
public boolean onKey(View v, int keyCode, KeyEvent event) {
if (editText.getText().toString().contains("1")){
editText.setError("Input contains the number 1!");
}
return false;
}
}
See preview below:
Android Studio EditText Set Error
Toast
A Toast gives a user a simple feedback about an action that is performed in the app.
See sample code below:
Toast.makeText(this, "Sample text", Toast.LENGTH_SHORT).show();
See preview below:
Android Studio Toast
AlertDialog
A dialog in general is a small window that asks the user to make a decision or enter additional information.
See sample code below:
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setTitle("Sample title");
builder.setMessage("Sample text");
builder.setPositiveButton("Done", (dialog, which) -> dialog.dismiss());
AlertDialog alertDialog = builder.create();
alertDialog.show();
See preview below:
Android Studio AlertDialog
Advanced
This section will talk about more advanced functions available in Android.