Java Immutables Library：检查所有Optional是否为空？

Question

I'd like to determine whether all Optional members of an immutable are empty. Is there a way to do this automatically without checking all the known Optionals by hand?

I'm concerned that even if do write a check for each Optional member someone will come along later and add an Optional field without updating that method.

Answer 1

It may change in the future, but I think you can try take a look at the overloaded builder methods generated for optional members:

For an optional attribute named opt , where elements are of type T

opt(T) sets present value for T

opt(Optional<T>) specifies present or absent

A Example

SomeValue.java

@Value.Immutable
public abstract class SomeValue {

    public abstract int foo();
    public abstract Optional<Object> obj();
    public abstract com.google.common.base.Optional<Double> d();
}

TestImmutables.java

public class TestImmutables {
    public static void main(String [] args) {
        SomeValue someValue = ImmutableSomeValue.builder().foo(2).build();

        for (Method method : someValue.getClass().getDeclaredMethods()) {
            System.out.print(method.getName() + "(");
            for (Type t : method.getGenericParameterTypes()) {
                System.out.print(t);
                System.out.print(",");
            }
            System.out.println(")");
        }
    }
}

Output

Each line is a method, pay attention to the methods generated for optional members.

builder()
equalTo(class immutables.ImmutableSomeValue,)
withObj(class java.lang.Object,)                           < obj
withObj(java.util.Optional<java.lang.Object>,)             < obj
withD(com.google.common.base.Optional<java.lang.Double>,)  < d
withD(double,)                                             < d
d()
withFoo(int,)
foo()
obj()
equals(class java.lang.Object,)
toString()
hashCode()
copyOf(class immutables.SomeValue,)

Basically you are looking for two overloads, each with exactly one parameter, and if parameter type of one is T , the parameter type of the other is SomeOptional<T> .