程式中經常會用到數字比較，但是你認為1000 == 1000 和 100 == 100比較值是否相同呢？
integer a = 1000 , b = 1000;
system.out.println(a == b);
integer c = 100 , d = 100;
system.out.println(c == d);
false
true
integer會將-127~128加入到快取陣列中，所以兩次宣告得100是指向同一物件得。
我們可以通過反射，獲取到該陣列中維護得數字：
class cache = integer.class.getdeclaredclasses()[0];
field mycache = cache.getdeclaredfield("cache");
mycache.setaccessible(true);
integer newcache = (integer) mycache.get(cache);
system.out.println(newcache.length);
for (integer integer : newcache)
256
-128,-127,-126,-125,-124,-123,-122,-121,-120,-119,-118,-117,-116,-115,-114,-113,-112,-111,-110,-109,-108,-107,-106,-105,-104,-103,-102,-101,-100,-99,-98,-97,-96,-95,-94,-93,-92,-91,-90,-89,-88,-87,-86,-85,-84,-83,-82,-81,-80,-79,-78,-77,-76,-75,-74,-73,-72,-71,-70,-69,-68,-67,-66,-65,-64,-63,-62,-61,-60,-59,-58,-57,-56,-55,-54,-53,-52,-51,-50,-49,-48,-47,-46,-45,-44,-43,-42,-41,-40,-39,-38,-37,-36,-35,-34,-33,-32,-31,-30,-29,-28,-27,-26,-25,-24,-23,-22,-21,-20,-19,-18,-17,-16,-15,-14,-13,-12,-11,-10,-9,-8,-7,-6,-5,-4,-3,-2,-1,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,
class cache = integer.class.getdeclaredclasses()[0];
field mycache = cache.getdeclaredfield("cache");
mycache.setaccessible(true);
integer newcache = (integer) mycache.get(cache);
system.out.println(newcache.length);
newcache[132] = newcache[133];
system.out.println(newcache[132]);
int a = 2;
int b = a + a;
system.out.printf("%d + %d = %d", a, a, b);
256
52 + 2 = 5
2+2 = 4 結果應該在快取的第132位，但是我們將133位的5換給了他，所以結果就變為5
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