What is the difference between an int and an Integ

Question

I was reading More Joel on Software when I came across Joel Spolsky saying something about a particular type of programmer knowing the difference between an int and an Integer in Java/C# (Object Oriented Programming Languages).

So, what is the difference?

Answer 1

Java:

int, double, long, byte, float, double, short, boolean, char - primitives. Used for hold the basic data types supported by the language. the primitive types are not part of the object hierarchy, and they do not inherit Object. Thet can'be pass by reference to a method.

Double, Float, Long, Integer, Short, Byte, Character, and Boolean, are type Wrappers, packaged in java.lang. All of the numeric type wrappers define constructors that allow an object to be constructed from a given value, or a string representation of that value. Using objects can add an overhead to even the simplest of calculations.

Beginning with JDK 5, Java has included two very helpful features: autoboxing and autounboxing. Autoboxing/unboxing greatly simplifies and streamlines code that must convert primitive types into objects, and vice versa.

Example of constructors:

Integer(int num)
Integer(String str) throws NumberFormatException
Double(double num)
Double(String str) throws NumberFormatException

Example of boxing/unboxing:

class ManualBoxing {
        public static void main(String args[]) {
        Integer objInt = new Integer(20);  // Manually box the value 20.
        int i = objInt.intValue();  // Manually unbox the value 20
        System.out.println(i + " " + iOb); // displays 20 20
    }
}

Example of autoboxing/autounboxing:

class AutoBoxing {
    public static void main(String args[]) {
        Integer objInt = 40; // autobox an int
        int i = objInt ; // auto-unbox
        System.out.println(i + " " + iOb); // displays 40 40
    }
}

P.S. Herbert Schildt's book was taken as a reference.

Answer 2

An int and Integer in Java and C# are two different terms used to represent different things. It is one of the the primitive data types that can be assigned to a variable that can store exactly. One value of its declared type at a time.

For example:

int number = 7;

Where int is the datatype assigned to the variable number which holds the value seven. So an int is just a primitive not an object.

While an Integer is a wrapper class for a primitive data type which has static methods. That can be used as an argument to a method which requires an object, where as int can be used as an argument to a method which requires an integer value, that can be used for arithmetic expression.

For example:

Integer number = new Integer(5);

Answer 3

Regarding Java 1.5 and autoboxing there is an important "quirk" that comes to play when comparing Integer objects.

In Java, Integer objects with the values -128 to 127 are immutable (that is, for one particular integer value, say 23, all Integer objects instantiated through your program with the value 23 points to the exact same object).

Example, this returns true:

Integer i1 = new Integer(127);
Integer i2 = new Integer(127);
System.out.println(i1 == i2); //  true

While this returns false:

Integer i1 = new Integer(128);
Integer i2 = new Integer(128);
System.out.println(i1 == i2); //  false

The == compares by reference (does the variables point to the same object).

This result may or may not differ depending on what JVM you are using. The specification autoboxing for Java 1.5 requires that integers (-128 to 127) always box to the same wrapper object.

A solution? =) One should always use the Integer.equals() method when comparing Integer objects.

System.out.println(i1.equals(i2)); //  true

More info at java.net Example at bexhuff.com

Answer 4

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 heep memory.

reference from "David Gassner" Java Essential Training.

Answer 5

int is predefined in library function c# but in java we can create object of Integer

Answer 6

One more thing that I don't see in previous answers: In Java the primitive wrappers classes like Integer, Double, Float, Boolean... and String are suposed to be invariant, so that when you pass an instance of those classes the invoked method couldn't alter your data in any way, in opositión with most of other classes, which internal data could be altered by its public methods. So that this classes only has 'getter' methods, no 'setters', besides the constructor.

In a java program String literals are stored in a separate portion of heap memory, only a instance for literal, to save memory reusing those instances