Variables and Types

Java code on variables and Types

      

Although Java is object oriented, not all types are objects (note this down). It is built on top of basic variable types called primitives.
Here is a list of all primitives in Java:

• byte (number, 1 byte)
• short (number, 2 bytes)
• int (number, 4 bytes)
• long (number, 8 bytes)
• float (float number, 4 bytes)
• double (float number, 8 bytes)
• char (a character, 2 bytes)
• boolean (true or false, 1 byte)

Java is a strong typed language, which means variables need to be defined before we use them.

                                        Numbers

To declare  and assign a number use the following syntax:

    int myNumber;
    myNumber = 5;

Or you can combine them:

int myNumber = 5;

To define a floating point number, use the following syntax:

double d = 4.5;
d = 3.0;

If you want to use float, you will have to cast:

float f = (float) 4.5;

Or, You can use this:

float f = 4.5f (f is a shorter way of casting float)

                                Characters and Strings

In Java, a character is it's own type and it's not simply a number, so it's not common to put an ASCII value in it, there is a special syntax for chars:

char c = 'g';

String is not a primitive. It's a real type, but Java has special treatment for String.
Here are some ways to use a string:

// Create a string with a constructor
String s1 = new String("Who let the dogs out?");
// Just using "" creates a string, so no need to write it the previous way.
String s2 = "Who who who who!";
// Java defined the operator + on strings to concatenate:
String s3 = s1 + s2;

There is no operator overloading in Java! The operator + is only defined for strings, you will never see it with other objects, only primitives.
You can also contact string to primitives:

int num = 5;
String s = "I have " + num + " cookies"; //Be sure not to use "" with primitives.

                                           Boolean

Every comparison operator in java will return the type Boolean that not like other languages can only accept two special values: true or false.

boolean b = false;
b = true;

boolean toBe = false;
b = toBe || !toBe;
if (b) {
    System.out.println(toBe);
}

int children = 0;
b = children; // Will not work
if (children) { // Will not work
    // Will not work
}

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