What is the difference between Integer and int in

Question

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");

Answer 1

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")).

Answer 2

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.

Answer 3

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);

Answer 4

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)

Answer 5

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.

Answer 6

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<Integer>).