java - Why does this return false and true? -

java - Why does this return false and true? -

public class test { public static final double default_double = 12.0; public static final long default_long = 1l; public static double converttodouble(object o) { homecoming (o instanceof number) ? ((number) o).doublevalue() : default_double; } public static long converttolong(object o) { homecoming (o instanceof number) ? ((number) o).longvalue() : default_long; } public static void main(string[] args){ system.out.println(converttodouble(null) == default_double); system.out.println(converttolong(null) == default_long); } }

edit

the ternary operator some type conversions under hood. in case mixing primitives , wrapper types, in case wrapper types gets unboxed, result of ternary operator "re-boxed":

if 1 of sec , 3rd operands of primitive type t, , type of other result of applying boxing conversion (§5.1.7) t, type of conditional look t.

so code equivalent (apart typo longvalue should doublevalue):

public static void main(string[] args){ double d = 12.0; system.out.println(d == default_double); long l = 1l; system.out.println(l == default_long); }

long values can cached on jvms , == comparing can hence homecoming true. if made comparisons equals true in both cases.

note if utilize public static final long default_long = 128l; , try:

long l = 128l; system.out.println(l == default_long);

it print false, because long values cached between -128 , +127 only.

note: jls requires char, byte , int values between -127 , +128 cached not long. code might print false twice on different jvm.

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