Internal working of Integer class

Question

I wanted to know some internal working of Integer class.

For example we can write:

Integer num = 9;

I wanted to know how an Integerclass is created in this case, as we have not created any Object. How does it works internally?

Answer 1

This is called autoboxing, a feature introduced in Java 5. The Java compiler transforms your statement into:

Integer num = Integer.valueOf(9);

You can read more about autoboxing here:

• http://docs.oracle.com/javase/tutorial/java/data/autoboxing.html
• http://docs.oracle.com/javase/1.5.0/docs/guide/language/autoboxing.html

Answer 2

This concept is called auto-boxing. The compiler will change your code to

Integer num = Integer.valueOf(9);

and continue compiling from there...