The Java TM Tutorial

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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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