Integer a = 25; equals to Integer a = Integer.valueOf(25);, it's called Auto Boxing and happens on compilation time.
Integer class maintains an internal IntegerCache, ranges from -128 to 127
Integer.valueOf will use IntegerCache if its in range of -128 to 127. other than that, Integer will create new Integer object.
public static Integer valueOf(int var0) {
return var0 >= -128 && var0 <= Integer.IntegerCache.high ? Integer.IntegerCache.cache[var0 + 128] : new Integer(var0);
}