Java built-in data types

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Java data types

• Data types specify the type of data that can be stored inside Java Variables.
• Java is a statically-typed language. This means that all variables must be declared before they can be used.

Java has 9 built-in data types:

• 8 Primitive Data Types + String type

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Primitive Data Types

There are 8 different primitive data types:

1. boolean type
2. byte type
3. short type
4. int type
5. long type
6. double type
7. float type
8. char type

Tipo	Operatori	Esempio	Intervallo	Space
byte	+ - * / %	27 + 1	-128…127	1 byte
short	+ - * / %	27 + 1	-32768…32767	2 byte
int	+ - * / %	27 + 1	-2147483648…2147483647	4 byte
long	+ - * / %	27 + 1	-1e9…1e9	8 byte
float	+ - * / %	3.14 * 5.01e23	7 cifre decimali significative	4 byte
double	+ - * / %	3.14 * 5.01e23	15 cifre decimali significative	8 byte
boolean	&& || !	true || false	true, false	1 byte
char	+ -	‘a’	Tutti i caratteri codificati con unicode	2 byte
String	+ -	“Hello” + “World”

oss: Strings are not primitive data types

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boolean type

• The boolean data type has two possible values, either true or false.
• Default value: false

class Main {
  public static void main(String[] args) {
    	
    boolean flag = true;
    System.out.println(flag);    // prints true
  }
}

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byte type

• The byte data type can have values from -128 to 127 (8-bit signed two’s complement integer).
• If it’s certain that the value of a variable will be within -128 to 127, then it is used instead of int to save memory.
• Default value: 0

class Main {
  public static void main(String[] args) {
 
    byte range;
    range = 124;
    System.out.println(range);    // prints 124
  }
}

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short type

• The short data type in Java can have values from -32768 to 32767 (16-bit signed two’s complement integer).
• If it’s certain that the value of a variable will be within -32768 and 32767, then it is used instead of other integer data types (int, long).
• Default value: 0

class Main {
  public static void main(String[] args) {
    	
    short temperature;
    temperature = -200;
    System.out.println(temperature);  // prints -200
  }
}

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int type

• The int data type can have values from $-2^{31}$ to $2^{31}-1$ (32-bit signed two’s complement integer).
• Default value: 0

class Main {
  public static void main(String[] args) {
    	
    int range = -4250000;
    System.out.println(range);  // print -4250000
  }
}

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long type

• The long data type can have values from $-2^{63}$ to $2^{63}-1$ (64-bit signed two’s complement integer).
• Default value: 0

Warning

You must write the literal with the f ant the and

long a = 84489094021L;
long b = 84489094021;   // integer number too large
 
// when you don't put a L at the end of the number it is casted to a int

class LongExample {
  public static void main(String[] args) {
    	
    long range = -42332200000L;
    System.out.println(range);    // prints -42332200000
  }
}

Notice, the use of L at the end of -42332200000. This represents that it’s an integer of the long type.

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double type

• The double data type is a double-precision 64-bit floating point.
• It should never be used for precise values such as currency.
• Default value: 0.0 (0.0d)

class Main {
  public static void main(String[] args) {
    	
    double number = -42.3;
    System.out.println(number);  // prints -42.3
  }
}

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float type

• The float data type is a single-precision 32-bit floating point.
• It should never be used for precise values such as currency.
• Default value: 0.0 (0.0f)

Warning

You must write the literal with the f ant the and

float a = 12.2f;
float b = 12.3;    // Error: incompatible types

class Main {
  public static void main(String[] args) {
    	
    float number = -42.3f;
    System.out.println(number);  // prints -42.3
  }
}

Notice that we have used -42.3f instead of -42.3in the above program. It’s because -42.3 is a double literal.

To tell the compiler to treat -42.3 as float rather than double, you need to use f or F.

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char type

• It’s a 16-bit Unicode character.
• The minimum value of the char data type is '\u0000' (0) and the maximum value of the is '\uffff'.
• Default value: '\u0000'

class Main {
  public static void main(String[] args) {
    	
    char letter = '\u0051';
    System.out.println(letter);  // prints Q
 
	char letter1 = '9';
    System.out.println(letter1);  // prints 9
    	
    char letter2 = 65;
    System.out.println(letter2);  // prints A
  }
}

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String type

Java also provides support for character strings via java.lang.String class. Strings in Java are not primitive types. Instead, they are objects.

String myString = "Java Programming";

Here, myString is an object of the String class. To learn more, visit Java Strings.

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