Exploring Java Data Types in Depth - datacouch-io/spark-java GitHub Wiki

In this section, we'll delve deeper into Java data types. As mentioned earlier, Java requires variables to be specified with a data type. Here's a recap of some common data types:

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

Data types are divided into two groups:

  • Primitive data types - includes byte, short, int, long, float, double, boolean and char
  • Non-primitive data types - such as String, Arrays and Classes (you will learn more about these in a later chapter)

Primitive Data Types

A primitive data type specifies the size and type of variable values, and it has no additional methods.

There are eight primitive data types in Java:

Data Type Size Description
byte 1 byte Stores whole numbers from -128 to 127
short 2 bytes Stores whole numbers from -32,768 to 32,767
int 4 bytes Stores whole numbers from -2,147,483,648 to 2,147,483,647
long 8 bytes Stores whole numbers from -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
float 4 bytes Stores fractional numbers from 3.4eāˆ’038 to 3.4e+038. Sufficient for storing 6 to 7 decimal digits
double 8 bytes Stores fractional numbers from 1.7eāˆ’308 to 1.7e+038. Sufficient for storing 15 decimal digits
boolean 1 byte Stores true or false values
char 2 bytes Stores a single character/letter

Numbers

Primitive number types are divided into two groups:

Integer types stores whole numbers, positive or negative (such as 123 or -456), without decimals. Valid types are byte, short, int and long. Which type you should use, depends on the numeric value.

Floating point types represents numbers with a fractional part, containing one or more decimals. There are two types: float and double.

Even though there are many numeric types in Java, the most used for numbers are int (for whole numbers) and double (for floating point numbers).
Integer Types
Byte

The byte data type can store whole numbers from -128 to 127. This can be used instead of int or other integer types to save memory when you are certain that the value will be within -128 and 127:

byte myNum = 100;
System.out.println(myNum);
Short

The short data type can store whole numbers from -32768 to 32767:

short myNum = 6666;
System.out.println(myNum);
Int

The int data type can store whole numbers from -2147483648 to 2147483647. In general, and in our tutorial, the int data type is the preferred data type when we create variables with a numeric value.

int myNum = 23333333;
System.out.println(myNum);
Long

The long data type can store whole numbers from -9223372036854775808 to 9223372036854775807. This is used when int is not large enough to store the value. Note that you should end the value with an "L":

long myNum = 15000000000L;
System.out.println(myNum);
Floating Point Types

You should use a floating point type whenever you need a number with a decimal, such as 9.99 or 3.14515.

Float

The float data type can store fractional numbers from 3.4eāˆ’038 to 3.4e+038. Note that you should end the value with an "f":

float myNum = 5.75f;
System.out.println(myNum);
Double

The double data type can store fractional numbers from 1.7eāˆ’308 to 1.7e+038. Note that you should end the value with a "d":

double myNum = 19.99d;
System.out.println(myNum);

Q: Use float or double? S: The precision of a floating point value indicates how many digits the value can have after the decimal point. The precision of float is only six or seven decimal digits, while double variables have a precision of about 15 digits. Therefore it is safer to use double for most calculations.

Booleans

A boolean data type is declared with the boolean keyword and can only take the values true or false:

boolean isJavaFun = true;
boolean isCodingBoring = false;
System.out.println(isJavaFun);     // Outputs true
System.out.println(isCodingBoring);   // Outputs false

Boolean values are mostly used for conditional testing, which you will learn more about in a later chapter.

Characters

The char data type is used to store a single character. The character must be surrounded by single quotes, like 'A' or 'c':

char myGrade = 'A';
System.out.println(myGrade);

Non-Primitive Data Types

Non-primitive data types are called reference types because they refer to objects.

The 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-primitve 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.

Strings

The String data type is used to store a sequence of characters (text). A String in Java is a non-primitive data type, because it refers to an object. The String object has methods that is used to perform certain operations on strings. (Don't worry if you don't understand the term "object" just yet. We will learn more about strings and objects in a later chapter.)

String values must be surrounded by double quotes:

String myCat = "I'm a cat-person";
System.out.println(myCat);

Examples of non-primitive types are Strings, Arrays, Classes, Interface, etc. You will learn more about these in a later chapter.