Summary of the JNI

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Trail: Java Native Interface

Lesson: Summary of the JNI

Congratulations! You have learned a great deal about the JNI. To help you remember everything you have learned, this section summarizes the JNI functions and mapping types.

Mapping Between JNI and Native Types

The following two tables summarize how Java types map to native types and the rules for encoding Java types in native signatures.

Primitive Types and Native Equivalents

Java Type Native Type Size in bits

boolean jboolean 8, unsigned

byte jbyte 8

char jchar 16, unsigned

short jshort 16

int jint 32

long jlong 64

float jfloat 32

double jdouble 64

void void n/a

Encoding for Java Type Signatures

Signature	Java Programming Language Type
`Z`	`boolean`
`B`	`byte`
`C`	`char`
`S`	`short`
`I`	`int`
`J`	`long`
`F`	`float`
`D`	`double`
`L` fully-qualified-class ;	fully-qualified-class
`[` type	type`[]`
`(` arg-types `)` ret-type	method type

JNI String Handling Functions

GetStringChars


GetStringLength
GetStringUTFChars
GetStringUTFLength
NewString
NewStringUTF
ReleaseStringChars

ReleaseStringUTFChars

JNI Array Handling Functions

GetArrayLength


Get<type>ArrayElements

GetBooleanArrayElements
GetByteArrayElements
GetCharArrayElements
GetDoubleArrayElements
GetFloatArrayElements
GetIntArrayElements
GetLongArrayElements
GetShortArrayElements

Release<type>ArrayElements
Get<type>ArrayRegion
Set<type>ArrayRegion
GetObjectArrayElement

SetObjectArrayElement

JNI Method Handling Functions

GetObjectClass


 GetMethodID 
 GetStaticMethodID 
Call<returntype>Method

   CallBooleanMethod
   CallByteMethod
   CallCharMethod
   CallDoubleMethod
   CallFloatMethod
   CallIntMethod
   CallLongMethod
   CallObjectMethod
   CallShortMethod
   CallVoidMethod
CallStatic<returntype>Method
CallNonvirtual<returntype>Method
Call<returntype>MethodV

Call<returntype>MethodA

JNI Member Variable Handling Functions

GetFieldID


GetStaticFieldID
Get<type>Field

   GetBooleanField 
   GetByteField 
   GetCharField 
   GetDoubleField 
   GetFloatField 
   GetIntField 
   GetLongField 
   GetObjectField 
   GetShortField 
Set<type>Field
GetStatic<type>Field

SetStatic<type>Field

JNI Exception Handling Functions

ExceptionClear


ExceptionDescribe

ExceptionOccurred

JNI Local and Global Reference Handling Functions

NewGlobalRef


DeleteGlobalRef

DeleteLocalRef

JNI Thread Synchronization Functions

MonitorEnter

MonitorExit

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Java Type	Native Type	Size in bits
`boolean`	`jboolean`	8, unsigned
`byte`	`jbyte`	8
`char`	`jchar`	16, unsigned
`short`	`jshort`	16
`int`	`jint`	32
`long`	`jlong`	64
`float`	`jfloat`	32
`double`	`jdouble`	64
`void`	`void`	n/a