Pass reference to method instead of value (or something like that) - JAVA

Question

I have multiple objects with value stored in -

object.getList().get(0).getSomeObject.getName(0)

It's possible, that list is empty so-

object.getList().get(0)

throws a NPE

I want to pass-

object.getList().get(0).getSomeObject.getName()

to another method and handle the exception there.

For example:

// calling the method
myMethod(object.getList().get(0).getSomeObject.getName());

public void myMethod(Object o){
    try {
        String name = o;
    }catch (Exception e){
        // do something
    }
}

Is it possible to do something like that -

EvaluateLaterObject elo = new EvaluateLaterObject(object.getList().get(0).getSomeObject.getName());
myMethod(elo);

public void myMethod(EvaluateLaterObject elo){
    try {
        String name = elo.getValue();
    }catch (Exception e){
        // do something
    }
}

Thank you in advance!

Probably duplicate of this https://stackoverflow.com/questions/18198176/java-8-lambda-function-that-throws-exception — SME_Dev, Sep 25 '19 at 12:06

Michael · Accepted Answer · 2019-09-25T12:13:39.117

2

You can use a functional interface such as Supplier and a lambda

myMethod(() -> object.getList().get(0).getSomeObject.getName());

public void myMethod(Supplier<String>){
    try {
        String name = elo.get();
    }catch (Exception e){
        // do something
    }
}

If you want to support any exception, you'll need to define your own functional interface e.g.

@FunctionalInterface
interface ThrowableSupplier<T>
{
    T get() throws Throwable;
}

edited Sep 25 '19 at 12:13

answered Sep 25 '19 at 12:01

Michael

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Only works for unchecked (runtime) exceptions though. – SME_Dev Sep 25 '19 at 12:04
@SME_Dev Right. Trivially avoided though. – Michael Sep 25 '19 at 12:08

Joop Eggen · Answer 2 · 2019-09-25T12:12:57.947

Either what already was given by Michael

Supplier<String> objectSupplier = () -> object.getList().get(0).getSomeObject.getName();

public void myMethod(Supplier<String> objectSupplier){
    try {
        String name = objectSupplier.get();
    }catch (Exception e){
        // do something
    }
}

Which does not really handle the exception.

Or use the optionality. Assuming the list items have class ListItem and getSomeObject is of class Item:

Optional<String> nameOpt = object.getList().stream()  // Stream<ListItem>
        .findFirst()                                  // Optional<ListItem>
        .map(ListItem::getSomeObject)                 // Optional<Item>
        .map(Item::getName);                          // Optional<String>

public void myMethod(Optional<String> nameOpt){
    nameOpt.ifPresent(name -> System.out.println(name));
    String nm = nameOpt.orElse("(No Name)");
}

Right. The correct approach here is to avoid the NPE in the first place. — Michael, Sep 25 '19 at 12:11

Pass reference to method instead of value (or something like that) - JAVA

2 Answers2