What is the difference between Integer and int in Java

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For example why can you do   int n   9    But not   Integer n   9    And you can do   Integer parseInt  1      But not   int parseInt  1

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This is taken from Java  The Complete Reference  Ninth Edition  Java uses primitive types  also called simple types   such as int or double  to hold the basic data types supported by the language  Primitive types  rather than objects  are used for these quantities for the sake of performance  Using objects for these values would add an unacceptable overhead to even the simplest of calculations  Thus  the primitive types are not part of the object hierarchy  and they do not inherit Object  Despite the performance benefit offered by the primitive types  there are times when you will need an object representation  For example  you can   t pass a primitive type by reference to a method  Also  many of the standard data structures implemented by Java operate on objects  which means that you can   t use these  object specific  data structures to store primitive types  To handle these  and other  situations  Java provides type wrappers  which are classes that encapsulate a primitive type within an object  Wrapper classes relate directly to Java   s autoboxing feature  The type wrappers are Double  Float  Long  Integer  Short  Byte  Character  and Boolean  These classes offer a wide array of methods that allow you to fully integrate the primitive types into Java   s object hierarchy

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To optimize the Java code runtime  int primitive type s  has been added including float  bool etc  but they come along with there wrapper classes so that if needed you can convert and use them as standard Java object along with many utility that comes as their member functions  such as Integer parseInt  1

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Integer refers to wrapper type in Java whereas int is a primitive type  Everything except primitive data types in Java is implemented just as objects that implies Java is a highly qualified pure object-oriented programming language  If you need  all primitives types are also available as wrapper types in Java  You can have some performance benefit with primitive types  and hence wrapper types should be used only when it is necessary   In your example as below   Integer n   9    the constant 9 is being auto-boxed  auto-boxing and unboxing occurs automatically from java 5 onwards  to Integer and therefore you can use the statement like that and also Integer n   new Integer 9   This is actually achieved through the statement Integer valueOf 9  intValue

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int is a primitive type  Variables of type int store the actual binary value for the integer you want to represent  int parseInt  1   doesn t make sense because int is not a class and therefore doesn t have any methods   Integer is a class  no different from any other in the Java language  Variables of type Integer store references to Integer objects  just as with any other reference  object  type  Integer parseInt  1   is a call to the static method parseInt from class Integer  note that this method actually returns an int and not an Integer    To be more specific  Integer is a class with a single field of type int  This class is used where you need an int to be treated like any other object  such as in generic types or situations where you need nullability   Note that every primitive type in Java has an equivalent wrapper class     byte has Byte short has Short int has Integer long has Long boolean has Boolean char has Character float has Float double has Double   Wrapper classes inherit from Object class  and primitive don t  So it can be used in collections with Object reference or with Generics   Since java 5 we have autoboxing  and the conversion between primitive and wrapper class is done automatically   Beware  however  as this can introduce subtle bugs and performance problems  being explicit about conversions never hurts

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An int variable holds a 32 bit signed integer value  An Integer  with capital I  holds a reference to an object of  class  type Integer  or to null   Java automatically casts between the two  from Integer to int whenever the Integer object occurs as an argument to an int operator or is assigned to an int variable  or an int value is assigned to an Integer variable  This casting is called boxing unboxing   If an Integer variable referencing null is unboxed  explicitly or implicitly  a NullPointerException is thrown    In the above text  the term  variable  means local variable  field or parameter

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int is a primitive type that represent an integer  whereas Integer is an Object that wraps int  The Integer object gives you more functionality  such as converting to hex  string  etc   You can also use OOP concepts with Integer  For example  you can use Integer for generics  i e  Collection lt Integer gt

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int is a primitive type and not an object  That means that there are no methods associated with it  Integer is an object with methods  such as parseInt    With newer java there is functionality for auto boxing  and unboxing   That means that the compiler will insert Integer valueOf int  or integer intValue   where needed  That means that it is actually possible to write  Integer n   9    which is interpreted as  Integer n   Integer valueOf 9

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int is a primitive data type while Integer is a Reference or Wrapper Type  Class  in Java   after java 1 5 which introduce the concept of autoboxing and unboxing you can initialize both int or Integer like this   int a  9 Integer a   9    both valid After Java 1 5       why Integer parseInt  1    but not int parseInt  1         Integer is a Class defined in jdk library and parseInt   is a static method belongs to Integer Class  So  Integer parseInt  1    is possible in java  but int is primitive type  assume like a keyword  in java  So  you can t call parseInt   with int

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An Integer is pretty much just a wrapper for the primitive type int  It allows you to use all the functions of the Integer class to make life a bit easier for you   If you re new to Java  something you should learn to appreciate is the Java documentation  For example  anything you want to know about the Integer Class is documented in detail   This is straight out of the documentation for the Integer class    The Integer class wraps a value of the primitive type int in an object  An object of type Integer contains a single field whose type is int

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In Java int is a primitive data type while Integer is a Helper class  it is use to convert for one data type to other   For example            double doubleValue   156 5d           Double doubleObject    new Double doubleValue            Byte myByteValue   doubleObject byteValue              String myStringValue   doubleObject toString      Primitive data types are store the fastest available memory where the Helper class is complex and store in heap memory   reference from  David Gassner  Java Essential Training

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Integer is an wrapper class Object and int is primitive type  This difference plays huge role when you want to store int values in a collection  because they accept only objects as values  until jdk1 4   JDK5 onwards because of autoboxing it is whole different story

[java] What is the difference between Integer and int in Java?

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