Determine if an Object is of Primitive Type

1. Overview

Sometimes we need to determine if an object is of primitive type, especially for wrapper primitive types. However, there are no built-in methods in the standard JDK to achieve this.

In this quick tutorial, we'll see how to implement a solution using core Java. Then we'll take a look at how we can achieve this using a couple of commonly used libraries.

2. Primitives and Wrapper Classes

There are nine predefined objects to represent eight primitives and a void type in Java. Each primitive type has a corresponding Wrapper Class.

To learn more about Primitives and Objects, please see this article.

The java.lang.Class.isPrimitive() method can determine if the specified object represents a primitive type. However,  it does not work on the wrappers for primitives.

For example, the following statement returns false:

Integer.class.isPrimitive();

Now let's take a look at different ways we can achieve this.

3. Using Core Java

First, let's define a HashMap variable which stores the wrapper and the primitive type classes:

private static final Map<Class<?>, Class<?>> WRAPPER_TYPE_MAP;
static {
    WRAPPER_TYPE_MAP = new HashMap<Class<?>, Class<?>>(16);
    WRAPPER_TYPE_MAP.put(Integer.class, int.class);
    WRAPPER_TYPE_MAP.put(Byte.class, byte.class);
    WRAPPER_TYPE_MAP.put(Character.class, char.class);
    WRAPPER_TYPE_MAP.put(Boolean.class, boolean.class);
    WRAPPER_TYPE_MAP.put(Double.class, double.class);
    WRAPPER_TYPE_MAP.put(Float.class, float.class);
    WRAPPER_TYPE_MAP.put(Long.class, long.class);
    WRAPPER_TYPE_MAP.put(Short.class, short.class);
    WRAPPER_TYPE_MAP.put(Void.class, void.class);
}

If the object is a primitive wrapper class, we can look it up from the predefined HashMap variable with java.utils.Map.ContainsKey() method.

Now we can create a simple utility method to determine if the object source is of a primitive type:

public static boolean isPrimitiveType(Object source) {
    return WRAPPER_TYPE_MAP.containsKey(source.getClass());
}

Let's validate that this works as expected:

assertTrue(PrimitiveTypeUtil.isPrimitiveType(false));
assertTrue(PrimitiveTypeUtil.isPrimitiveType(1L));
assertFalse(PrimitiveTypeUtil.isPrimitiveType(StringUtils.EMPTY));

4. Using Apache Commons – ClassUtils.isPrimitiveOrWrapper()

Apache Commons Lang has a ClassUtils.isPrimitiveOrWrapper method that can be used to determine if a class is a primitive or a wrapper of primitive.

First, let's add the commons-lang3 dependency from Maven Central to our pom.xml:

<dependency>
    <groupId>org.apache.commons<groupId>
    <artifactId>commons-lang3<artifactId>
    <version>3.5<version>
<dependency>

Then let's test it:

assertTrue(ClassUtils.isPrimitiveOrWrapper(Boolean.False.getClass()));
assertTrue(ClassUtils.isPrimitiveOrWrapper(boolean.class));
assertFalse(ClassUtils.isPrimitiveOrWrapper(StringUtils.EMPTY.getClass()));

5. Using Guava – Primitives.isWrapperType()

Guava provides a similar implementation via the Primitives.isWrapperType method.

Again, let's add the dependency from Maven Central first:

<dependency>
    <groupId>com.google.guava<groupId>
    <artifactId>guava<artifactId>
    <version>29.0-jre<version>
<dependency>

Likewise, we can test it using:

assertTrue(Primitives.isWrapperType(Boolean.FALSE.getClass()));
assertFalse(Primitives.isWrapperType(StringUtils.EMPTY.getClass()));

However, the Primitives.isWrapperType method won't work on the primitive class, the following code will returns false:

assertFalse(Primitives.isWrapperType(boolean.class));

6. Conclusion

In this tutorial, we illustrated how to determine if an object can represent a primitive data type using our own implementation using Java. Then we took a look at a couple of popular libraries that provide utility methods for achieving this.

The complete code can be found over on Github.