Java: How to determine if type is any of primitive/wrapper/String, or something else

Question

Is there a single method in JDK or common basic libraries which returns true if a type is a primitive, a primitive wrapper, or a String?

I.e.

Class<?> type = ...
boolean isSimple = SomeUtil.isSimple( type );

The need for such information can be e.g. to check whether some data can be represented in formats like JSON. The reason for a single method is to be able to use it in expression language or templates.

Prirmitives are not objects, so they are not instances of any classes. All is simple here. To check on wrapper: a instanceof Number. To check on String: str instanceof String. — DmitryKanunnikoff, Jul 30 '14 at 14:15
possible duplicate of [Determining if an Object is of primitive type](http://stackoverflow.com/questions/709961/determining-if-an-object-is-of-primitive-type) — dimo414, Jul 30 '14 at 14:19
@DmitryTsechoev: 1) You misread the question. There are also `Class` objects for primitive types (see [Double.TYPE](http://docs.oracle.com/javase/8/docs/api/java/lang/Double.html#TYPE)) and those should be tested, not the instances of the class / the primitive variable / field. 2) That a object is a instance of `Number` does not imply it's a primitive wrapper (e.g. `BigInteger` is not a primitive wrapper, but it's a `Number`) — fabian, Jul 30 '14 at 14:39

score 33 · Accepted Answer · answered Jul 30 '14 at 14:14

33

I found something:

Commons Lang: (would have to combine with check for String)

ClassUtils.isPrimitiveOrWrapper()

Spring:

BeanUtils.isSimpleValueType()

This is what I want, but would like to have it in Commons.

answered Jul 30 '14 at 14:14

Ondra Žižka

43,948
41
217
277

Boann · Answer 2 · 2014-07-30T14:43:23.913

24

Is there a single method which returns true if a type is a primitive

Class.isPrimitive:

Class<?> type = ...;
if (type.isPrimitive()) { ... }

Note that void.class.isPrimitive() is true too, which may or may not be what you want.

a primitive wrapper?

No, but there are only eight of them, so you can check for them explicitly:

if (type == Double.class || type == Float.class || type == Long.class ||
    type == Integer.class || type == Short.class || type == Character.class ||
    type == Byte.class || type == Boolean.class) { ... }

a String?

Simply:

if (type == String.class) { ... }

That's not one method. I want to determine whether it's one of those named or something else, in one method.

Okay. How about:

public static boolean isPrimitiveOrPrimitiveWrapperOrString(Class<?> type) {
    return (type.isPrimitive() && type != void.class) ||
        type == Double.class || type == Float.class || type == Long.class ||
        type == Integer.class || type == Short.class || type == Character.class ||
        type == Byte.class || type == Boolean.class || type == String.class;
}

edited Jul 30 '14 at 14:43

answered Jul 30 '14 at 14:22

Boann

48,794
16
117
146

That's not one method. I want to determine whether it's one of those named or something else, in one method. – Ondra Žižka Jul 30 '14 at 14:39
You say "there are only eight of them". What about `BigInteger`, `BigDecimal` and friends? Can I easily recognise them as also being primitive-like? – Steve Pitchers Apr 26 '17 at 17:39
4

@StevePitchers The Java Language Specification [defines the eight primitive types explicitly](https://docs.oracle.com/javase/specs/jls/se8/html/jls-4.html#jls-4.2). `BigInteger` and friends are reference types (and quite complicated ones!), although they are intended to operate like primitives by being immutable. Actually that immutability is broken, since they forgot to make those classes `final`. A better candidate for a "primitive-like" reference type would be `String`, or a ["value-based"](https://docs.oracle.com/javase/8/docs/api/java/lang/doc-files/ValueBased.html) class like `Optional`. – Boann Apr 26 '17 at 18:01

icza · Answer 3 · 2014-07-30T14:32:54.010

3

The java.util.Class type has the proper methods:

Class<?> type = ...

boolean primitive = type.isPrimitive();
boolean string_ = type == String.class;
boolean array = type.isArray();
boolean enum_ = type.isEnum();
boolean interf_ = type.isInterface();

edited Jul 30 '14 at 14:32

answered Jul 30 '14 at 14:23

icza

389,944
63
907
827

1) That's not a single method, 2) What if it's a subclass of String (i.e. in some Java-using script language) – Ondra Žižka Jul 30 '14 at 14:38
1

1) I just offered other similar methods which may be of interest to the questioner. 2) `java.lang.String` is a `final` class, so `type` cannot be a subclass of `String`. You can't extend `java.lang.String`. – icza Jul 30 '14 at 14:40
Class being final means nothing nowadays. See Javassist. – Ondra Žižka Jul 30 '14 at 14:49
If you want to manipulate byte code or the memory, then there is no good solution to anything because it can be modified in the background or the displayed value can be altered. – icza Jul 30 '14 at 14:52

score 0 · Answer 4 · answered Oct 01 '19 at 08:48

0

Guava provides the Primitives class with Primitives.isWrapperType(class) which returns true for Integer, Long, ...

answered Oct 01 '19 at 08:48

Joachim Sauer

302,674
57
556
614

score -3 · Answer 5 · answered Jul 30 '14 at 14:16

-3

Integer, Float, Character, etc are not primitives; they are wrapper classes which serve as containers for primitives. They are reference objects. True primitives are types like int, float, double, long, byte, char, and boolean -- non-object types. There's a big difference, since

value instanceof Float

won't even compile if "value" is a primitive. "String" is also not a primitive -- it's a type of object. 'null' is also not a primitive -- it's a literal value.

answered Jul 30 '14 at 14:16

CarlosZ

73
1
8

1

You should have informed yourself before posting this answer, e.g. in the "TYPE Field for Primitive Type Wrappers" section on http://docs.oracle.com/javase/tutorial/reflect/class/classNew.html . There are `Class` objects for primitive types!!!!! – fabian Jul 30 '14 at 14:24

score -5 · Answer 6 · answered Jul 30 '14 at 14:54

No there is not. And should not be. For tree difference question you should provide tree different answers.

public static <T> boolean  isPrimitive(Class<T> klass) {

    return klass.isPrimitive();
}

public static <T> boolean isString(Class<T> klass) {

    return String.class == klass; //String is final therefor you can not extend it.

}

public static <T> boolean isPrimitiveWrapper(Class<T> klass) {

    return Character.class == klass || Boolean.class == klass || klass.isAssignableFrom(Number.class);

}

`isPrimitiveWrapper(BigInteger.class)` will return true, you need to check all wrapper types explicitly. — Celos, Sep 19 '16 at 08:05

Java: How to determine if type is any of primitive/wrapper/String, or something else

6 Answers6

Linked

Related