What is .intValue() in Java?

Question

l.get(i); will return Integer and then calling intValue(); on it will return the integer as type int.

Converting an int to Integer is called boxing.
Converting an Integer to int is called unboxing
And so on for conversion between other primitive types and their corresponding Wrapper classes.

Since java 5, it will automatically do the required conversions for you(autoboxing), so there is no difference in your examples if you are working with Java 5 or later. The only thing you have to look after is if an Integer is null, and you directly assign it to int then it will throw NullPointerException.

Prior to java 5, the programmer himself had to do boxing/unboxing.

As you noticed, intValue is not of much use when you already know you have an Integer. However, this method is not declared in Integer, but in the general Number class. In a situation where all you know is that you have some Number, you'll realize the utility of that method.

The Object returned by l.get(i) is an instance of the Integer class.

intValue() is a instance method of the Integer class that returns a primitive int.

See Java reference doc... http://docs.oracle.com/javase/6/docs/api/java/lang/Integer.html#intValue()

Java support two types of structures first are primitives, second are Objects.

Method that you are asking, is used to retrieve value from Object to primitive.

All java types that represent number extend class Number. This methods are in someway deprecated if you use same primitive and object type since [autoboxing] was implemented in Java 1.5.

int - primitive

Integer - object

Before Java 1.5 we was force to write

int i = integer.intValue();

since Java 1.5 we can write

int i = integer;

Those methods are also used when we need to change our type from Integer to long

long l = integer.longValue();

Consider this example:

Integer i = new Integer(10);
Integer j = new Integer(10);
if (!(i == j)) {
    System.out.println("Surprise, doesn't match!");
}
if (i.intValue() == j.intValue()) {
    System.out.println("Cool, matches now!");
}

which prints

Surprise, doesn't match!
Cool, matches now!

That proves that intValue() is of great relevance. More so because Java does not allow to store primitive types directly into the containers, and very often we need to compare the values stored in them. For example:

oneStack.peek() == anotherStack.peek() 

doesn't work the way we usually expects it to work, while the below statement does the job, much like a workaround:

oneStack.peek().intValue() == anotherStack.peek().intValue()

get(i) will return Integer object and will get its value when you call intValue().In first case, automatically auto-unboxing happens.