CODEWITHSUNDEEP
java
Qshbx
Qshbx

Reputation: 51

How do I avoid lots of checking in Java?

When writing a Java program, I face a problem as follows:

Map<Object, Map<Object, Map<Object, Object>>> map = new HashMap<>();
/**
* put operations
**/
Map<Object, Map<Object, Object>> a = null;
Map<Object, Object> b = null;
Object c = null;
a = map.get(/*some object*/);
if(a != null) {
    b = a.get(/*some object*/);
}
if(b != null) {
    c = b.get(/*some object*/);
}
if(c != null) {
    /*do what I want to do*/
}

If I want to be sure c is not null, I need to add an "if" three times to ensure that the code can run without exception. Is there a better way to do it?

Upvotes: 0

Views: 114

Answers (3)

wassgren
wassgren

Reputation: 19201

I think that the getOrDefault-method of the Map interface could work here. Especially if you combine it with the Optional class as follows:

Map<Object, Map<Object, Map<Object, Object>>> map = new HashMap<>();
Map<Object, Map<Object, Object>> a = map.getOrDefault("", Collections.emptyMap());
Map<Object, Object> b = a.getOrDefault("", Collections.emptyMap());
Optional.ofNullable(b.get("")).ifPresent(c -> {/* Do what I want to do */});

This way you simply use getOrDefault to retrieve empty maps (which I personally like better than null values. The Optional.ofNullable is a null-safe way of creating an Optional object and you can do what you want to do in the lambda expression.

Both Optional and Map.getOrDefault are part of Java 8.

Upvotes: 0

Marko Živanović
Marko Živanović

Reputation: 906

Encapsulate required functionality in a class implementing something like this:

interface ThreeKeysMap {
    void put(Object keyA, Object keyB, Object keyC, Object value);
    Object get(Object keyA, Object keyB, Object keyC);
}

Alternatively, you could create a class for your composite key:

public class ThreeKey {
    public Object keyA;
    public Object keyB;
    public Object keyC;

    // TODO: MUST override equals and hashCode methods or map won't work!!!!
}

and use it as a key for your map: Map<ThreeKey, Object> map = new HashMap<>();

Upvotes: 2

amit
amit

Reputation: 178411

You can create a class Key<T,E> that will hold your first pairs of objects, and than create a map

Map<Key<T,E>, Object>

This seems much more neat to me, because it seems you use the first two objects as a key, and the nested dictionary approach is less elegant for such a task.

Remember that if you follow this approach - you have to override equals() and hashCode(), and depending on usages - sometimes also compareTo()

Upvotes: 0

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