MODULE 4: DATA TYPES

Data Types

Data Types

• set of values together with a set of operations

• A type of data that can be stored

• How much memory an item occupies

• What types of operations can be performed on data

Java Data Types

Primitive data types & Reference data types

Primitive data types

A simple data type

Reference data types

Also known as Non-Primitive Data Type

More complex data types

Primitive Data Types

Integral, Floating, Textual, Logical

Integral Primitive Data Type

.byte, short, int, long

Floating Primitive Data Type

.float, double

Textual Primitive Data Type

.char

Logical Primitive Data Type

.boolean

String

• The String data type is used to store a sequence of characters (text). 

• String values must be surrounded by double quotes

Concatenation

• A numeric variable is concatenated to a String using the plus sign ( + )

• The entire expression becomes a String

• The println() method can accept a number or String

Main difference between primitive and non-primitive data types are:

• Primitive types are predefined (already defined) in Java. Non-primitive types are created by the programmer and is not defined by Java (except for String).

• Non-primitive types can be used to call methods to perform certain operations, while primitive types cannot.

• A primitive type has always a value, while non-primitive types can be null.

• A primitive type starts with a lowercase letter, while non-primitive types starts with an uppercase letter.

• The size of a primitive type depends on the data type, while non-primitive types have all the same size.

Type Conversion (Casting)

• when you assign a value of one primitive data type to another type.

• Used to avoid implicit type coercion

• Expression evaluated first, then type converted to dataTypeName

• Convert String to int or double

  Use methods from the built-in Java classes Integer and Double

Widening Casting (automatically), Narrowing Casting (manually)

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

Type-wrapper classes

• Each primitive type has a corresponding class contained in the java.lang package

• Include methods to process primitive type values

Integer.parseInt()

Double.parseDouble()