Integer Class, auto-boxing and Caching

Today, i decided to search a little the latest j2sdk sources. My initial search began with the usage of final modifier in the signature of a method. What is its exact usage, etc.

I wrote some sample programs and decompiled them, finding nothing of interest. Then i tried to investigate auto-boxing. I wrote a sample program that calls a method that has an Integer class as parameter. Something like that:

public void bar(Integer i) { ... }
	
int i = 1;
System.out.println(i);

When i used auto-boxing, the compiler used the Integer.valueOf(int) method. So i started searching if it is more optimized to use auto-boxing, or not.

When i changed the i variable to Integer type, and called normally the constructor of the Integer class, i realized that the constructor was invoked normally, with int as parameter.

The mystery solved when i read the original Integer class sources.

The contructor simply instantiates a new Integer object. On the other hand, the Integer.valueOf(int) does the following:

public static Integer valueOf(int i) {pre
	final int offset = 128;
	if (i >= -128 && i <= 127) { // must cache 
		return IntegerCache.cache[i + offset];
	}
	
	return new Integer(i);
}