What s the difference between primitive and reference types

Question

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

User · Answer

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).

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);

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

Primitive data type  The primitive data type is a basic type provided by a programming language as a basic building block  So it s predefined data types  A primitive type has always a value  It storing simple value   It specifies the size and type of variable values  so the size of a primitive type depends on the data type and it has no additional methods   And these are reserved keywords in the language  So we can t use these names as variable  class or method name  A primitive type starts with a lowercase letter  When declaring the primitive types we don t need to allocate memory   memory is allocated and released by JRE-Java Runtime Environment in Java   8 primitive data types in Java                                                                                                                     Primitive type   Size      Description                                                                                                                                                                                            byte             1 byte    Stores whole numbers from -128 to 127                                                ---------------- --------- -----------------------------------------------------------------------------------    short            2 bytes   Stores whole numbers from -32 768 to 32 767                                          ---------------- --------- -----------------------------------------------------------------------------------    int              4 bytes   Stores whole numbers from -2 147 483 648 to 2 147 483 647                            ---------------- --------- -----------------------------------------------------------------------------------    long             8 bytes   Stores whole numbers from -9 223 372 036 854 775 808 to 9 223 372 036 854 775 807    ---------------- --------- -----------------------------------------------------------------------------------    float            4 bytes   Stores fractional numbers  Sufficient for storing 6 to 7 decimal digits              ---------------- --------- -----------------------------------------------------------------------------------    double           8 bytes   Stores fractional numbers  Sufficient for storing 15 decimal digits                  ---------------- --------- -----------------------------------------------------------------------------------    char             2 bytes   Stores a single character letter or ASCII values                                     ---------------- --------- -----------------------------------------------------------------------------------    boolean          1 bit     Stores true or false values                                                          ---------------- --------- -----------------------------------------------------------------------------------    Reference data type  Reference data type refers to objects  Most of these types are not defined by programming language except for String  arrays in JAVA   Reference types of value can be null  It storing an address of the object it refers to  Reference or non-primitive data types have all the same size  and reference types can be used to call methods to perform certain operations   when declaring the reference type need to allocate memory  In Java  we used new keyword to allocate memory  or alternatively  call a factory method   Example   List lt  String  gt  strings   new ArrayList lt  gt          Calling  new   to instantiate an object and thereby allocate memory   Point point   Point 1 2                 Calling a factory method

[java] What's the difference between primitive and reference types?

Primitive Type

Reference Type

Wildcard Type

Void Type

Null Type

Union Type

Interference Type

Unknown Type

Var Type

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