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A conditional expression with numeric second and third operands of differing
types may give surprising results.
For example:
Object t = true ? Double.valueOf(0) : Integer.valueOf(0);
System.out.println(t.getClass()); // class java.lang.Double
Object f = false ? Double.valueOf(0) : Integer.valueOf(0);
System.out.println(f.getClass()); // class java.lang.Double !!
Despite the apparent intent to get a `Double` in one case, and an `Integer` in
the other, the result is a `Double` in both cases.
This is because the rules in
[JLS ยง 15.25.2](https://docs.oracle.com/javase/specs/jls/se9/html/jls-15.html#jls-15.25.2)
state that differing numeric types will undergo binary numeric promotion. As
such, the latter case is evaluated as:
Object f =
Double.valueOf(
false
? Double.valueOf(0).doubleValue()
: (double) Integer.valueOf(0).intValue());
To get a different type in the two cases, one can either explicitly cast the
operands to a non-boxable type:
Object f = false ? ((Object) Double.valueOf(0)) : ((Object) Integer.valueOf(0));
System.out.println(t.getClass()); // class java.lang.Integer
Or use if/else:
Object f;
if (false) {
f = Double.valueOf(0);
} else {
f = Integer.valueOf(0);
}
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