can you guess the output of this program?

[killutch]

public class Init{
	public static void main(String[] args){
		Integer a =10;
		Integer b = 10;
		if(a==b)System.out.println("same object");
		
		Integer c = 1000;
		Integer d = 1000;
		if(c!=d)System.out.println("not same object");
	}
}

apparently when a Boolean, Byte, Char, Short, Long, or Integer wrapper classes hold data that's a byte or smaller == is no longer a comparison between classes its between there primitive values but this doesn't apply to Double ha ha ha How in the word am I suppose to remember this stuff? No wonder the SCJP is supposed to be one of the hardest exams in the IT industry. Anyone have any interesting memorization strategies.

[eRaaaa]

?
-Djava.lang.Integer.IntegerCache.high=1000 and your statement isn`t longer correct :D

[doWhile]

See the JLS
Chapter*5.*Conversions and Promotions
to quote:

If the value p being boxed is true, false, a byte, or a char in the range \u0000 to \u007f, or an int or short number between -128 and 127 (inclusive), then let r1 and r2 be the results of any two boxing conversions of p. It is always the case that r1 == r2

The assumption it compares primitives is incorrect - it compares two identical (cached) objects

[killutch]

my bad. still weird though and figured i would share

[Tolls]

Integer a = 10;
...
Integer c = 1000;

In both those cases the compiler is autboxing the primitive on the right.
As part of autoboxing it essentially replaces the int with:

Integer a = Integer.valueOf(10);

valueOf() looks like this:

    public static Integer valueOf(int i) {
        if(i >= -128 && i <= IntegerCache.high)
            return IntegerCache.cache[i + 128]; // <-- get it from our cache.
        else
            return new Integer(i);
    }

which is where the magic that eRaaa and doWhile talk about occurs.