Definition:
Any data-type built-into a programing language is called primitive data type. Basic behavior of a primitive data type itself, however, cannot be changed.
There are 8 primitive data types in java. They are as follow:
1. byte
byte: The byte data type is an 8-bit signed two’s complement integer. It has a minimum value of -128 and a maximum value of 127 (inclusive). The byte data type can be useful for saving memory in large arrays, where the memory savings actually matters. They can also be used in place of int where their limits help to clarify your code; the fact that a variable’s range is limited can serve as a form of documentation.
Example:
byte v1 = 3; // 11
byte v2 = 5; // 101
byte min = -128; // 1000_0000 - first bit is sign bit
byte max = 127; // 0111_1111
2. short
short: The short data type is a 16-bit signed two’s complement integer. It has a minimum value of -32,768 and a maximum value of 32,767 (inclusive). As with byte, the same guidelines apply: you can use a short to save memory in large arrays, in situations where the memory savings actually matters.
Example:
short val = 89;
3. int
int: By default, the int data type is a 32-bit signed two’s complement integer, which has a minimum value of -231 and a maximum value of 231-1. In Java SE 8 and later, you can use the int data type to represent an unsigned 32-bit integer, which has a minimum value of 0 and a maximum value of 232-1. Use the Integer class to use int data type as an unsigned integer. See the section The Number Classes for more information. Static methods like compareUnsigned, divideUnsigned etc have been added to the Integer class to support the arithmetic operations for unsigned integers.
Example:
int val = 89;
4. long
long: The long data type is a 64-bit two’s complement integer. The signed long has a minimum value of -263 and a maximum value of 263-1. In Java SE 8 and later, you can use the long data type to represent an unsigned 64-bit long, which has a minimum value of 0 and a maximum value of 264-1. Use this data type when you need a range of values wider than those provided by int. The Long class also contains methods like compareUnsigned, divideUnsigned etc to support arithmetic operations for unsigned long.
Example:
long val = 89L;
5. float
float: The float data type is a single-precision 32-bit IEEE 754 floating point. Its range of values is beyond the scope of this discussion, but is specified in the Floating-Point Types, Formats, and Values section of the Java Language Specification. As with the recommendations for byte and short, use a float (instead of double) if you need to save memory in large arrays of floating point numbers. This data type should never be used for precise values, such as currency. For that, you will need to use the java.math.BigDecimal class instead. Numbers and Strings covers BigDecimal and other useful classes provided by the Java platform.
Example:
float val = 89.2f;
6. double
double: The double data type is a double-precision 64-bit IEEE 754 floating point. Its range of values is beyond the scope of this discussion, but is specified in the Floating-Point Types, Formats, and Values section of the Java Language Specification. For decimal values, this data type is generally the default choice. As mentioned above, this data type should never be used for precise values, such as currency.
Example:
double val = 89.2;
7. boolean
boolean: The boolean data type has only two possible values: true and false. Use this data type for simple flags that track true/false conditions. This data type represents one bit of information, but its “size” isn’t something that’s precisely defined.
Example:
boolean val = true;
8. char
char: The char data type is a single 16-bit Unicode character. It has a minimum value of ‘\u0000’ (or 0) and a maximum value of ‘\uffff’ (or 65,535 inclusive).
Example:
char val = '9';
char val = 65; // 'A'
In addition to the eight primitive data types listed above, the Java programming language also provides special support for character strings via the java.lang.String class. Enclosing your character string within double quotes will automatically create a new String object; for example,
String s = "this is a string";. String objects are immutable, which means that once created, their values cannot be changed. The String class is not technically a primitive data type, but considering the special support given to it by the language, you’ll probably tend to think of it as such. You’ll learn more about the String class in Simple Data Objects
Overflow of value
what happen if we assign a value out of data-type bound to its variable?
it will only get value of enough bits of its data-type of value, what you want to assign, to convert to value and assign to variable.
Example:
byte value1 = -128; // (1)...1111_1111_(1000_0000)
System.out.println(value1); // -128
byte value2 = -129; // (1)...1111_1111_(0111_1111)
System.out.println(value2); // 127
byte value2 = 129; // (0)...0000_0000_(1000_0001)
System.out.println(value2); // -127
byte value3 = 127; // (0)...0000_0000_(0111_1111)
System.out.println(value3); // 127
byte value3 = 128; // (0)...0000_0000_(1000_0000)
System.out.println(value4); // -128
When assigning value to a byte variable from int value, byte variable will only get 8 final bits of int value. First bit for sign bit, 7 remain bits for value, that is why we have value like above example!
Compare between primitive value and its box
We have heard that when compare objects, java will compare their references? Yes, but it not work with primitive value! When you compare with primivive values, wrapper class of it or mix of them, it will convert to primitive value and then compare in primitive value.
Example:
int val1 = 8;
Integer val2 = new Integer(8);
if (val1 == val2) {
System.out.println("equal");
} else {
System.out.println("not equal");
}
// output : "equal"
Example 2:
int val1 = 8;
Integer val2 = null;
if (val1 == val2) {
System.out.println("equal");
} else {
System.out.println("not equal");
}
// Output: NullPointerException
Yeah, we cannot convert null to a primitive value, of sure!
Reference link: https://docs.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html