How to Determine if an Object is of Primitive Type in Java?

Determining if an Object is of Primitive Type

When working with arrays of objects, it may be necessary to determine which objects are primitive types. While attempting to use the Class.isPrimitive() method, some users may encounter false results due to auto-boxing.

Understanding Auto-Boxing

Auto-boxing is a feature in Java that automatically converts primitive values to their corresponding wrapper classes when used as objects. For example, the primitive int is automatically converted to its wrapper class, Integer.

Correct Approach

To accurately determine if an object is of primitive type, it is necessary to check whether its type is a "wrapper for primitive" instead of using Class.isPrimitive(). This can be achieved by comparing the object's class with a set of known wrapper classes.

Customizing for Specific Types

The following code snippet includes a utility method, isWrapperType, that can be used to determine if an object's type is a wrapper type. It compares the object's class against a pre-defined set of wrapper classes and returns a boolean result.

<code class="java">import java.util.*;

public class Test {
    public static void main(String[] args) {
        System.out.println(isWrapperType(String.class));
        System.out.println(isWrapperType(Integer.class));
    }

    private static final Set<Class<?>> WRAPPER_TYPES = getWrapperTypes();

    public static boolean isWrapperType(Class<?> clazz) {
        return WRAPPER_TYPES.contains(clazz);
    }

    private static Set<Class<?>> getWrapperTypes() {
        Set<Class<?>> ret = new HashSet<>();
        ret.add(Boolean.class);
        ret.add(Character.class);
        ...
        return ret;
    }
}</code>

Conclusion

By using this custom approach, developers can accurately determine if an object within an Object[] array is of a primitive type, taking into account the effects of auto-boxing.

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