CODEWITHSUNDEEP
javamethodsnulldouble
Tremendo JuanPablo
Tremendo JuanPablo

Reputation: 11

null detection for double method

I'm employing a private lib. One of the objects has a method that delivers either a double or a null.

How could I perform:

if (object.method != null) {
    // do some numeric operations with the returned value
}

Additional details:

library = org.apache.commons.collections4.map
class = LRUmap
method = get

My code is:

public class ExampleNode extends GeneralNode {
    private LRUMap<Integer, Double> cache;

    public ExampleNode() {
        this.setCache(new LRUMap<Integer,Double>(100));
    }    

    public void setCache(LRUMap<Integer, Double> lruMap) {
        this.cache = lruMap;
    }

    public double getDatumCacheDebug(int llave){
        return this.cache.get((Object)llave,false);
    }
}

And then I call:

//outside ExampleNode
    if ( actualNode.getDatumCacheDebug(k) != null ) {

Eclipse Neon3 says: "The operator != is undefined for the argument type(s) double,null."

Upvotes: 0

Views: 158

Answers (3)

Patricia Shanahan
Patricia Shanahan

Reputation: 26185

The signature of the library method is:

public V get(Object key,
    boolean updateToMRU)

in class LRUMap<K,V>

The returned value is a Double, and therefore could be null, but it is being unboxed to double before the null test:

public double getDatumCacheDebug(int llave){
    return this.cache.get((Object)llave,false);
}

I suggest changing the signature of this method to return Double instead of double, so that the information about whether the result was null is preserved and can be tested. Otherwise, it will throw NullPointerException if get returns null.

Upvotes: 0

strash
strash

Reputation: 1321

A working variant of your code will be:

if (object.method != 0) {
    // do some numeric operations with the returned value
}

But it is better practice to refactor your method object.method() to return a specific number for your "null cases"- example: a method that is searching for an index in a list - returns the index number if found and -1 if not found or exception is thrown during the search (a null case for the search)

Upvotes: 0

SilverNak
SilverNak

Reputation: 3381

When the method returns a primitive double (and not the Double class), it can never be null. A primitive value will always have a value of its type (i. e. you can't do double d = null;).

Thus this check would never return true and the compiler does not allow you to do it.

Upvotes: 1

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