I'm reading SCJP Java 6 by Kathy Sierra and Bert Bates and this book is confusing me so much. On page 245 they state that the following code below.
Integer i1 = 1000; Integer i2 = 1000; if(i1 != i2) System.out.println("different objects"); //Prints output different objects
Then on the very next page they have the following code
Integer i3 = 10; Integer i4 = 10; if(i3 == i4) System.out.println("same objects"); //Prints output same objects
I'm so confused! When I try this out on my own it seems that you cannot use the == to compare the same way you would use equals() method. Using the == always gives me 'false' even if the Integer variables are set to the same value (i.e. 10). Am I correct? Using the == to compare the same Integer object (with same values) will always result in 'false'
The key to the answer is called object interning. Java interns small numbers (less than 128), so all instances of
n in the interned range are the same. Numbers greater than or equal to 128 are not interned, hence
Integer(1000) objects are not equal to each other.