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 3.4e−038 to 3.4e+038. Note that you should end the value with an "f":
Example
float myNum = 5.75f;
System.out.println(myNum);
Double
The 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":
Example
double myNum = 19.99d;
System.out.println(myNum);
Use float or double?
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.
Scientific Numbers
A floating point number can also be a scientific number with an "e" to indicate the power of 10:
Example
float f1 = 35e3f;
double d1 = 12E4d;
System.out.println(f1);
System.out.println(d1);
Booleans
A boolean data type is declared with the boolean keyword and can only take the values true or false:
Example
boolean isJavaFun = true;
boolean isFishTasty = false;
System.out.println(isJavaFun);
System.out.println(isFishTasty);
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':
Example
char myGrade = 'B';
System.out.println(myGrade);
Alternatively, you can use ASCII values to display certain characters:
Example
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.
Strings
The String data type is used to store a sequence of characters (text). String values must be surrounded by double quotes:
Example
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 are 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
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.
