I want to make a generic method that determines whether the first parameter is null, and if it is the case returns the second which is the default, else returns the first.
Can I make this possible?
I don't know how to implement it properly.
public static <T> ifNull(Object parameter, Object default, Class<T> type) {
return type.cast(parameter == null ? default: parameter));
}
Note: this code doesn't work for real, it's just an example.
I think this link might be useful: is there a Java equivalent to null coalescing operator (??) in C#?
public static <T> T coalesce(T one, T two) {
return one != null ? one : two; }
or
public static <T> T coalesce(T... params) {
for (T param : params)
if (param != null)
return param;
return null; }
You can use something like this,
public static <T> T getValOrDefault(T value, T defaultValue) {
return value != null ? value : defaultValue;
}
I am not 100 % sure, but i think you want something like that:
public static <T> T ifNull(T parameter, T defaultValue) {
return parameter == null ? defaultValue: parameter;
}
If you are receiving two nullable objects of Object type and want to type-cast them dynamically to the given type by passing an in instance of Class<T> to your method, I think you were intending to achieve this:
public static <T> Optional<T> ifNull(Object first, Object second, Class<T> type) {
return Optional.ofNullable(type.cast(first))
.or(() -> Optional.ofNullable(type.cast(second)));
}
Class<T> object represents a class or interface
Method cast() will cast the given object to a particular type T, if it's the object is assignable to that type, otherwise a ClassCastException will be thrown. Note that compiler will not issue warnings for such way of downcasting (which is always potentially unsafe).
Optional is a special container-object introduced with Java 8 in order to be used a return type in cases when the resulting value could be null. Optional object might either contain a value or be empty, but it would never be null (if you are following good practices and not using optional as a field, method parameter and not storing it anywhere)
Optional.ofNullable() creates optional object containing the given value, if it's non-null, otherwise returns an empty optional.
Method or() will substitute the current optional object, if it is empty, with the provided optional.
The result of method execution will be the following:
Optional[first] --(first == null)--> Optional[second] --(second == null)--> empty optional
Note:
<T> or wild card <? extends Number> between modifiers and return type or keyword void (in the method above <T> is ageneric type parameter and Optional<T> is a return type).default is a keyword in Java.