Introduction to Java Programming

Java is a popular programming language, created in 1995.

It is used for:

• Mobile applications (specially Android apps)

• Desktop applications

• Web applications

• Web servers and application servers

• Games

• Database connection

• And much, much more!

Why Use Java?

• Java works on different platforms (Windows, Mac, Linux, Raspberry Pi, etc.)

• It is one of the most popular programming language in the world

• It is easy to learn and simple to use

• It is open-source and free

• It is secure, fast and powerful

• It has a huge community support (tens of millions of developers)

• Java is an object oriented language which gives a clear structure to programs and allows code to be reused, lowering development costs

• As Java is close to C++ and C#, it makes it easy for programmers to switch to Java or vice versa

Operators are used to perform operations on variables and values.

In the example below, we use the + operator to add together two values:

Example

int x = 100 + 50;

Although the + operator is often used to add together two values, like in the example above, it can also be used to add together a variable and a value, or a variable and another variable:

Example

int sum1 = 100 + 50;        // 150 (100 + 50)

int sum2 = sum1 + 250;      // 400 (150 + 250)

int sum3 = sum2 + sum2;     // 800 (400 + 400)

Java Data Types

As explained in the previous chapter, a variable in Java must be a specified data type:

Example

int myNum = 5;               // Integer (whole number)

float myFloatNum = 5.99f;    // Floating point number

char myLetter = 'D';         // Character

boolean myBool = true;       // Boolean

String myText = "Hello";     // String

Java Type Casting

Type casting is when you assign a value of one primitive data type to another type.

In Java, there are two types of casting:

• Widening Casting (automatically) - converting a smaller type to a larger type size
  byte -> short -> char -> int -> long -> float -> double
  
  

• Narrowing Casting (manually) - converting a larger type to a smaller size type
  double -> float -> long -> int -> char -> short -> byte

Java supports the usual logical conditions from mathematics:

• Less than: a < b

• Less than or equal to: a <= b

• Greater than: a > b

• Greater than or equal to: a >= b

• Equal to a == b

• Not Equal to: a != b

You can use these conditions to perform different actions for different decisions.

Java has the following conditional statements:

• Use if to specify a block of code to be executed, if a specified condition is true

• Use else to specify a block of code to be executed, if the same condition is false

• Use else if to specify a new condition to test, if the first condition is false

• Use switch to specify many alternative blocks of code to be executed

Loops

Loops can execute a block of code as long as a specified condition is reached.

Loops are handy because they save time, reduce errors, and they make code more readable.