Java Data Types
Java Data Types
As explained in the previous chapter, a variable in Java must be a specified data type:
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
- 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:
|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. Sufficient for storing 6 to 7 decimal digits|
|double||8 bytes||Stores fractional numbers. Sufficient for storing 15 decimal digits|
|boolean||1 bit||Stores true or false values|
|char||2 bytes||Stores a single character/letter or ASCII values|
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
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:
Even though there are many numeric types in Java, the most used for numbers
int (for whole numbers) and
double (for floating point numbers). However, we will describe them all as you continue to
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 data type can store whole numbers from -32768 to 32767:
short myNum = 5000; System.out.println(myNum);
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 = 100000; System.out.println(myNum);
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 data type can store fractional numbers from 3.4e−038 to 3.4e+038. Note that you should end the value with an "f":
float myNum = 5.75f; System.out.println(myNum);
double data type can store fractional numbers from 1.7e−308 to 1.7e+308. Note that you should end the value with a "d":
double myNum = 19.99d; System.out.println(myNum);
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.
A floating point number can also be a scientific number with an "e" to indicate the power of 10:
float f1 = 35e3f; double d1 = 12E4d; System.out.println(f1); System.out.println(d1);
A boolean data type is declared with the
boolean keyword and can only take the values
boolean isJavaFun = true; boolean isFishTasty = false; System.out.println(isJavaFun); // Outputs true System.out.println(isFishTasty); // Outputs false
Boolean values are mostly used for conditional testing, which you will learn more about in a later chapter.
char data type is used to store a
single character. The character must be
surrounded by single quotes, like 'A' or 'c':
char myGrade = 'B'; System.out.println(myGrade);
Alternatively, you can use ASCII values to display certain characters:
char a = 65, b = 66, c = 67; System.out.println(a); System.out.println(b); System.out.println(c);
Tip: A list of all ASCII values can be found in our ASCII Table Reference.
String data type is used to store a sequence of characters (text). String values must be surrounded by double quotes:
String greeting = "Hello World"; System.out.println(greeting);
The String type is so much used and integrated in Java, that some call it "the special ninth type".
A String in Java is actually 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.
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
- 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
- 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.