Types

Primitive types

JNI primitive types, how they represented in Swift:

JNI	Swift
jbyte	Int8
jshort	Int16
jint	Int32
jlong	Int64
jchar	UInt16
jboolean	Bool
jfloat	Float
jdouble	Double

Pure primitive types can be passed as method arguments directly:

let intValue: Int32 = 9.41
let floatValue: Float = 9.41
let doubleValue: Double = 9.41
object.callVoidMethod(name: "setValues", args: intValue, floatValue, doubleValue)

These values cannot be nil and are always represented in the JNI signature as primitives.

Primitive type objects

However, if the Java side expects full object types like java.lang.Integer or java.lang.Long, you need to use their Swift wrapper equivalents listed below:

Swift Type	Swift Wrapper	Java Type
Int8	JInt8 (JByte)	java/lang/Byte
Int16	JInt16 (JShort)	java/lang/Short
Int32	JInt32 (JInt, JInteger)	java/lang/Integer
Int64	JInt64 (JLong)	java/lang/Long
Bool	JBool	java/lang/Boolean
Float	JFloat	java/lang/Float
Double	JDouble	java/lang/Double
UInt16	JUInt16 (JChar, JCharacter)	java/lang/Character

These values can be nil.

Usage Example:

let nilDoubleObject: JDouble? = nil
let doubleObject: JDouble? = 9.41
let double: Double = 9.41

// Object Double is NULL
object.callVoidMethod(name: "sendDouble", args: nilDoubleObject)

// Object Double is NOT NULL: 9.41
object.callVoidMethod(name: "sendDouble", args: doubleObject)

// Primitive Double: 9.41
object.callVoidMethod(name: "sendDouble", args: double)

Corresponding Kotlin Code:

fun sendDouble(value: Double) {
    Log.d("CHECK", "Primitive Double: $value")
}
fun sendDouble(value: Double?) {
    if (value != null) {
        Log.d("CHECK", "Object Double is NOT NULL: $value")
    } else {
        Log.d("CHECK", "Object Double is NULL")
    }
}

Non-primitive type objects

This includes all other Java object types like String, custom classes, collections, etc. They are represented in Swift as JObject or their specific subclasses (e.g., JString for java.lang.String).

These values can also be nil.

To know more please head to → Objects, → Classes, and → Signature