问题
This is a past exam question and I was wondering what a primitive type and reference type are first off? With an array I know the a reference type is where the array is composed of objects or variables, but a primitive type is where you would create the array with just int or strings. (right?)
How do you think you would answer the question on the test and be given good credit? Without really referring directly to an primitive ARRAY type... Is there a way to do it without that? Or do you think it would be fine to just explain it with the array.
回答1:
These are the primitive types in Java:
- boolean
- byte
- short
- char
- int
- long
- float
- double
All the other types are reference types: they reference objects.
This is the first part of the Java tutorial about the basics of the language.
回答2:
From book OCA JAVA SE 7
Just as men and women are fundamentally different (according to John Gray, author of Men Are from Mars, Women Are from Venus), primitive variables and object reference variables differ from each other in multiple ways. The basic difference is that primitive variables store the actual values, whereas reference variables store the addresses of the objects they refer to. Let’s assume that a class Person is already defined. If you create an int variable a, and an object reference variable person, they will store their values in memory as shown in figure 2.13.
int a = 77;
Person person = new Person();
回答3:
Primitive Data Types :
- Predefined by the language and named by a keyword
- Total no = 8
boolean
char
byte
short
integer
long
float
double
Reference/Object Data Types :
- Created using defined constructors of the classes
- Used to access objects
- Default value of any reference variable is null
- Reference variable can be used to refer to any object of the declared type or any compatible type.
回答4:
these are primitive data types
- boolean
- character
- byte
- short
- integer
- long
- float
- double
saved in stack in the memory which is managed memory on the other hand object data type or reference data type stored in head in the memory managed by GC
this is the most important difference
回答5:
Primitives vs. References
First :-
Primitive types are the basic types of data:
byte, short, int, long, float, double, boolean, char.
Primitive variables store primitive values.
Reference types are any instantiable class as well as arrays:
String, Scanner, Random, Die, int[], String[], etc.
Reference variables store addresses to locations in memory for where the data is stored.
Second:-
Primitive types store values but Reference type store handles to objects in heap space. Remember, reference variables are not pointers like you might have seen in C and C++, they are just handles to objects, so that you can access them and make some change on object's state.
Read more: http://javarevisited.blogspot.com/2015/09/difference-between-primitive-and-reference-variable-java.html#ixzz3xVBhi2cr
回答6:
As many have stated more or less correctly what reference and primitive types are, one might be interested that we have some more relevant types in Java. Here is the complete lists of types in java (as far as I am aware of (JDK 11)).
Primitive Type
Describes a value (and not a type).
11
Reference Type
Describes a concrete type which instances extend Object (interface, class, enum, array). Furthermore TypeParameter is actually a reference type!
Integer
Note: The difference between primitive and reference type makes it necessary to rely on boxing to convert primitives in Object instances and vise versa.
Note2: A type parameter describes a type having an optional lower or upper bound and can be referenced by name within its context (in contrast to the wild card type). A type parameter typically can be applied to parameterized types (classes/interfaces) and methods. The parameter type defines a type identifier.
Wildcard Type
Expresses an unknown type (like any in TypeScript) that can have a lower or upper bound by using super or extend.
? extends List<String>
? super ArrayList<String>
Void Type
Nothingness. No value/instance possible.
void method();
Null Type
The only representation is 'null'. It is used especially during type interference computations. Null is a special case logically belonging to any type (can be assigned to any variable of any type) but is actual not considered an instance of any type (e.g. (null instanceof Object) == false).
null
Union Type
A union type is a type that is actual a set of alternative types. Sadly in Java it only exists for the multi catch statement.
catch(IllegalStateException | IOException e) {}
Interference Type
A type that is compatibile to multiple types. Since in Java a class has at most one super class (Object has none), interference types allow only the first type to be a class and every other type must be an interface type.
void method(List<? extends List<?> & Comparable> comparableList) {}
Unknown Type
The type is unknown. That is the case for certain Lambda definitions (not enclosed in brackets, single parameter).
list.forEach(element -> System.out.println(element.toString)); //element is of unknown type
Var Type
Unknown type introduced by a variable declaration spotting the 'var' keyword.
var variable = list.get(0);
回答7:
The short answer is primitives are data types, while references are pointers, which do not hold their values but point to their values and are used on/with objects.
Primatives:
boolean
character
byte
short
integer
long
float
double
Lots of good references that explain these basic concepts. http://www.javaforstudents.co.uk/Types
来源：https://stackoverflow.com/questions/8790809/whats-the-difference-between-primitive-and-reference-types