Java String objects in Java Add pdf417 in Java Java String objects

22.5 Java String objects using barcode generation for swing control to generate, create pdf-417 2d barcode image in swing applications. USPS POSTNET Barcode We note that Get servlet pdf417 2d barcode StringUTFRegion() was not in the original JNI speci cation. It was added for Java 2 SDK version 1.2 (commonly called JDK 1.

2) meaning it has been around for several years now. Unfortunately, it can be easy to miss the documentation about GetStringUTFRegion() and a few other new JNI functions because of the way the JNI documentation is organized. Most of the JNI functions are described in the online docs [1] in the section titled JNI 1.

1 Speci cation . The enhancements added since Java 1.1 appear in the section labeled JNI Enhancements, below which are links to JNI Enhancements in version 1.

2 , and JNI Enhancements in version 1.4 . In order to see all the JNI functions, you need to follow the links to all three documents.

(Fortunately, this situation has improved with the J2SE 5.0 document set where all the JNI functions are combined into one document.) One might also come across some (scant) documentation (see the JNI Programmer s Guide [3]) referring to a SetStringUTFRegion() function that permits directly setting the characters in a region of a jstring.

This function would be analogous to the Set functions for array elements, to be discussed later. However, to the best of our knowledge, such a function does not really exist in JNI. The Web Course contains a simple string handling example in les called StringExample.

java and NativeString.cpp. The string handling example takes an input string and uses C code to reverse the order of the characters.

The reversed string is returned as the return value of the native method. Of course the same thing could be done purely in Java. The example is simply meant to illustrate the use of the JNI string handling functions.

When the native method declaration declares the method return to be String, as our nativeProcessString example does, the value returned to the calling Java code must be a Java String. To create one on the native side, the native code uses the NewStringUTF() function which takes a C array of UTF-8 characters as an input argument and creates and returns a jstring. When the jstring is returned to the calling Java code, it is converted to a Java String by the JNI subsystem.

The code to create the new jstring appears as follows, assuming that the C string reverse has already been populated with the reversed-order version of the input string:. jstring jreverse = jenv->NewStringUTF (reverse); return jreverse;. Like GetStringUT PDF-417 2d barcode for Java FChars(), NewStringUTF() must allocate memory, so it is written to return NULL and throw an OutOfMemoryError if memory for the new jstring cannot be allocated. In general, the returned value should be checked and appropriate action should be taken if it is NULL. Here, however, since we immediately return the value obtained from NewStringUTF() anyway, there is no explicit need to check for a NULL return.

. The Java Native Interface (JNI). There are a few PDF 417 for Java other JNI string handling functions, particularly GetStringChars() and ReleaseStringChars(). These are useful for getting string characters in Unicode format instead of UTF-8 characters. Doing so is not relevant to this book and is not discussed further.

. 22.6 Java primitive arrays Arrays in Java c PDF 417 for Java an be arrays of Java primitives (e.g. float[]) or arrays of Java objects.

Arrays of Java primitive types are treated similarly to Java strings in JNI. Both are objects on the Java side, both are passed to native methods as object references, and both have special types de ned in jni.h on the C side for convenience.

Object arrays are a bit more complicated than primitive arrays, and we discuss them in the next section. A Java primitive array of Java floats is passed to a JNI method as a jfloatArray. There are also jintArray, jbyteArray, jdoubleArray, etc.

types for the other Java primitives. Just like a jstring is not a C string, neither is a jfloatArray an array of C/C++ floats. And, just like with strings, JNI provides special functions for converting the various jxxxArray types into corresponding C/C++ arrays.

One of the special functions for converting jfloatArray types is getFloatArrayElements(), which returns a pointer to an array of C floats. Given a jfloatArray called the-jfloatarray, we obtain a C array as follows:. float* c-array = jenv->GetFloatArrayElements ( the-jfloatarray, NULL); if (c-array == NULL) { return 0.;. } // Use c-array servlet PDF-417 2d barcode in some way, and then ReleaseFloatArrayElements (the-jfloatarray, c-array, 0); ...

. Here we have con verted the-jfloatarray into an array of C floats. The JNI function GetFloatArrayElements() allocates the space for the C array, performs the conversion, and returns a pointer to the new C array. Since the function must allocate enough memory for the C array we must be sure to check the return value for NULL and respond accordingly, just like we did with GetStringUTFChars() above.

After c-array has been used, we must be certain to clean up by calling ReleaseFloatArrayElements(). Similar code applies for all the other primitive array types. During garbage collection on the Java side, Java arrays may be moved in memory without warning.

The JVM ensures that a garbage collection event does not impact behavior on the Java side. For native code, the JVM also guarantees that the C side array does not move in memory unexpectedly. It does so by either making a copy of the Java array elements for use on the C side, where the copy is not subject.

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