Strange behaviour or not?

Question

Hi all...I'm new in this forum and I have a question to you. I think my curiosity is about the compiler, so I post here.
I use Java SE 1.5 and 1.6. If I write a simple class like the following
public class Prova{
public static void main(String[] args){
Integer a1=128;
Integer a2=128;
/*1*/System.out.println(a1==a2);
/*2*/System.out.println(a1);
/*3*/System.out.println(a2);
I get the following strange result
/*1*/ prints true if a1 and a2 are both inizialized between -128 and 127 (exactly 256 values, the ones obtainable from a byte) and false for values less then -128 or bigger then 127...
Is this a strange behaviour or not? Why do I obtain such results?
please note that /*2*/ and /*3*/ ALWAYS print the declared values (in this case 128).
thank you!

Answer 1

Shadow-DK wrote:
From version 1.5 that declaration began correct and the result was similar to Integer i = new Integer(100);
No that wouldn't permit caching. Its like Integer i = Integer.valueOf(100);The caching MUST occur for values -128 thru 127, it may occur for other values. I would not rely on caching not occurring outside that range.
See [the language spec section on boxing conversion|http://java.sun.com/docs/books/jls/third_edition/html/conversions.html#5.1.7]
If you aren't sure what the compiler is doing, it can be informative to use the javap command with the -c option to view the classfile.
Usage: javap <options> <classes>...
where options include:
   -c                        Disassemble the code
   -classpath <pathlist>     Specify where to find user class files
   -extdirs <dirs>           Override location of installed extensions
   -help                     Print this usage message
   -J<flag>                  Pass <flag> directly to the runtime system
   -l                        Print line number and local variable tables
   -public                   Show only public classes and members
   -protected                Show protected/public classes and members
   -package                  Show package/protected/public classes
                             and members (default)
   -private                  Show all classes and members
   -s                        Print internal type signatures
   -bootclasspath <pathlist> Override location of class files loaded
                             by the bootstrap class loader
   -verbose                  Print stack size, number of locals and args for met
                             If verifying, print reasons for failureBruce