当一个可以为null时，java查找来自两种不同对象类型的两个数字中的最小值

Question

I'm trying to figure out the best way of grabbing the smallest of two numbers when the numbers are attributes inside of two different objects. Each, but not both, of the objects can be null, which can lead to null pointer exceptions. Each object has their own getValue() method, which will return a Long value. There's the basic if/else that I'd prefer not to do:

if (obj1 != null && obj2 != null) {  // neither object is null
    minValue = obj1.getValue() <= obj2.getValue() ? obj1.getValue() : obj2.getValue();
} else if (obj1 == null && obj2 != null) { // only obj1 is null
    minValue = obj2.getValue();
} else { // only obj2 is null (they can't both be null, so we don't need an if for the situation where they're both null)
    minValue = obj1.getValue();
}

I've tried some other things:

// can throw null pointer exception
Collections.min(Arrays.asList(obj1.getValue(), obj2.getValue()));

// while both objects have a getValue() method, they are of different types, so mapping doesn't work
Collections.min(Arrays.asList(obj1, obj2)
    .filter(obj -> obj != null)
    .map(obj -> obj.getValue()) // this line will fail since the methods correspond to different objects
    .collect(Collectors.toList()));

I feel like this should be a fairly easy problem, but my brain's not allowing it to work. There's due to be some min function where you can bipass a situation where the object can be null?

Answer 1

long minValue = Math.min(obj1 == null ? Long.MAX_VALUE : obj1.getValue(),
                         obj2 == null ? Long.MAX_VALUE : obj2.getValue());

Answer 2

I am not sure I fully understand your question, but if I do, something like this could work:

if(obj1 == null) 
   minValue = obj2.getValue();
else if(obj2 == null)
   minValue = obj1.getValue();
else minValue = obj1.getValue() < obj2.getValue() ? obj1.getValue() : obj2.getValue();

Answer 3

You could have a method that takes in your ObjType, does a null check and returns Long.MAX_VALUE, or the value if it's null.

public Long getVal(ObjType val)
{
    if(val != null)
    {
       return val.getValue();
    }
    return Long.MAX_VALUE;
}

then do

Math.min(obj1, obj2);