Integercache inner class for Java integer encapsulation class

Personal understanding, do not like to spray, welcome correction.

First look at the following code, guess what the output is

1         Integer a = ten; 2         Integer B = Ten; 3         System.out.println (A = = b); 4         A = +; 5         b = +; 6         System.out.println (A = = b); 7         A = +; 8         b = +; 9         System.out.println (A = = B);    

Do you think true true True or false false?

Naïve, look.

You're right, that's the hole!

In a logical case, Integer is the package type, and the result should be false false.

So let's see how this code executes, and that's what happens.

First, when you assign a value, the following function is called, and here comes a strange thing, integercache, it looks like the problem is here.

Next look at what the Integercache is what, the following is the source of the class

In the source code we see this class has a [-128,127] integer array cache (the upper bound of this array seems to be variable, but I do not have RT source package, so I do not know the details), so look at the integer assignment code, it is very clear

This determines whether the size of your assignment is contained within the Integercache cache array.

If a reference to the object is returned, and thus less than or equal to 127 is greater than or equal to-128, the result can be obtained by = = Comparison to True, because the reference is the same, The number of out-of-range calls the integer constructor to recreate an integer object so that the value is the same but the result is false due to a different reference

So judging whether the object's value is the same or using a.equals (b)

Integercache inner class for Java integer encapsulation class