Using JNIEnv : JNI « Development Class « Java
Using JNIEnv
/**
@version 1.10 1997-07-01
@author Cay Horstmann
*/
#include "Printf3.h"
#include <string.h>
#include <stdlib.h>
#include <float.h>
/**
@param format a string containing a printf format specifier
(such as "%8.2f"). Substrings "%%" are skipped.
@return a pointer to the format specifier (skipping the '%')
or NULL if there wasn't a unique format specifier
*/
char* find_format(const char format[])
{
char* p;
char* q;
p = strchr(format, '%');
while (p != NULL && *(p + 1) == '%') /* skip %% */
p = strchr(p + 2, '%');
if (p == NULL) return NULL;
/* now check that % is unique */
p++;
q = strchr(p, '%');
while (q != NULL && *(q + 1) == '%') /* skip %% */
q = strchr(q + 2, '%');
if (q != NULL) return NULL; /* % not unique */
q = p + strspn(p, " -0+#"); /* skip past flags */
q += strspn(q, "0123456789"); /* skip past field width */
if (*q == '.') { q++; q += strspn(q, "0123456789"); }
/* skip past precision */
if (strchr("eEfFgG", *q) == NULL) return NULL;
/* not a floating-point format */
return p;
}
JNIEXPORT void JNICALL Java_Printf3_fprint(JNIEnv* env, jclass cl,
jobject out, jstring format, jdouble x)
{
const char* cformat;
char* fmt;
jstring str;
jclass class_PrintWriter;
jmethodID id_print;
cformat = (*env)->GetStringUTFChars(env, format, NULL);
fmt = find_format(cformat);
if (fmt == NULL)
str = format;
else
{
char* cstr;
int width = atoi(fmt);
if (width == 0) width = DBL_DIG + 10;
cstr = (char*) malloc(strlen(cformat) + width);
sprintf(cstr, cformat, x);
str = (*env)->NewStringUTF(env, cstr);
free(cstr);
}
(*env)->ReleaseStringUTFChars(env, format, cformat);
/* now call ps.print(str) */
/* get the class */
class_PrintWriter = (*env)->GetObjectClass(env, out);
/* get the method ID */
id_print = (*env)->GetMethodID(env, class_PrintWriter, "print", "(Ljava/lang/String;)V");
/* call the method */
(*env)->CallVoidMethod(env, out, id_print, str);
}
/*
This program is a part of the companion code for Core Java 8th ed.
(http://horstmann.com/corejava)
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
import java.io.*;
/**
* @version 1.10 1997-07-01
* @author Cay Horstmann
*/
class Printf3
{
public static native void fprint(PrintWriter out, String format, double x);
static
{
System.loadLibrary("Printf3");
}
}
/*
This program is a part of the companion code for Core Java 8th ed.
(http://horstmann.com/corejava)
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
import java.io.*;
/**
* @version 1.10 1997-07-01
* @author Cay Horstmann
*/
class Printf3Test
{
public static void main(String[] args)
{
double price = 44.95;
double tax = 7.75;
double amountDue = price * (1 + tax / 100);
PrintWriter out = new PrintWriter(System.out);
Printf3.fprint(out, "Amount due = %8.2f\n", amountDue);
out.flush();
}
}
Printf3Test.zip( 2 k)