Data Types

In Java, there are 8 primitive data types. They are the basic building blocks for the language. You can build complex objects and applications based on these data types, similar to how you can create a skyscraper out of simple Lego pieces.

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

Integer Types

For negative and positive numbers without fractions, you have four choices: byte, short, int, and long.

Type Storage Range (Inclusive) Example
byte 1 byte -128 to 127 byte b = 127;
short 2 bytes –32,768 to 32,767 short s = 30000; short s1 = -32_000;
int 4 bytes –2,147,483,648 to 2,147,483, 647 (just over 2 billion) int i = 20;
long 8 bytes –9,223,372,036,854,775,808 to 9,223,372,036,854,775,807 long l = 100; long l1 = 100L; long l2 = 100l;

Byte

Note for each type, there is a storage associated with it. The storage space is called byte. Think of it like a bucket. It refers to how many bucket is needed to store the number. This is important when memory was expensive. But now, memory is usually not a factor for most computer, so most developers use int for simple numbers and long for large numbers.

Casting

Java automatically converts a smaller type number into a larger type because it is not losing any data.

byte b = 127;
int i = b;

However, to cast a larger type into a smaller type, you have to write the type you want to convert it to. For example, if you have an int (4 byte) and you want to convert it to a byte (1 byte), then there is a possibility that the number might not fit into the byte. Therefore, Java forces you to say, yes, I understand I might lose some data, convert it anyway.

int i = 129;
byte b = (byte)i; // casting from 4 bytes into 1 byte
// b becomes -127 because the maximum number a byte can be is 127

Decimal Types

Numbers with fractions

Type Storage requirements Range (Inclusive)
float 4 bytes Approximately ±3.40282347E+38F (6–7 significant decimal digits)
double 8 bytes Approximately ±1.79769313486231570E+308 (15 significant decimal digits)

Developers generally uses double because the precision is better. Because of the way double are store is not 100% correct, in the real world, we do not use double or float for money.

Casting

Java can automatically cast integers into float/double.

int i = 2000;
float f = i;

Because of the loss of precision, to cast from a decimal number into an integer, you have to explicitly say so.

float f = 3.14f;
int i = (int)f; //i is 3

char Type

The char type is a single character represented by a value enclosed in single quotes. It takes up 2 bytes.

char a = 'a';
char capA = 'A';
char semi = ';';
char num = '8';

Note '8' is NOT the same as the number 8 without quotes. One is a char, the other is an int.

You can use a number to represent a character. A is mapped to the number 65 so you can write it like this:

char numChar = 65; // 'A'

boolean Type

The boolean type has two values: false and true.

boolean t = true;
boolean f = false;

You can use it to store the result of a comparison because the comparison yields true or false.

boolean a = 1 > 0; // true
boolean b = 1 > 5; // false
boolean c = 1 == 1; // true
boolean d = 1 >= 5; // false
boolean e = 1 <= 5; // true
boolean f = 8 == '8'; // false

Is Java a true object oriented language?

No, because primitive types are not objects.

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