added solution for exercise 7_2_1

modified makefile

.cproject

@@ -77,6 +77,14 @@
 				<useDefaultCommand>true</useDefaultCommand>
 				<runAllBuilders>true</runAllBuilders>
 			</target>
+			<target name="java_exercises7_2_1_HelloJNI.h" path="jni" targetID="org.eclipse.cdt.build.MakeTargetBuilder">
+				<buildCommand>make</buildCommand>
+				<buildArguments/>
+				<buildTarget>java_exercises7_2_1_HelloJNI.h</buildTarget>
+				<stopOnError>true</stopOnError>
+				<useDefaultCommand>true</useDefaultCommand>
+				<runAllBuilders>true</runAllBuilders>
+			</target>
 		</buildTargets>
 	</storageModule>
 </cproject>

jni/java_exercises7_2_1_HelloJNI.c

+#include <jni.h>
+#include <stdio.h>
+#include "java_exercises7_2_1_HelloJNI.h"
+
+// Implementation of native method sayHello() of HelloJNI class
+JNIEXPORT void JNICALL Java_java_1exercises7_11_11_HelloJNI_sayHello(JNIEnv *env, jobject thisObj) {
+   printf("Hello World!\n");
+   return;
+}
+
+/*
+ * Class:     java_exercises7_2_1_HelloJNI
+ * Method:    intMethod
+ * Signature: (I)I
+ */
+JNIEXPORT jint JNICALL Java_java_1exercises7_12_11_HelloJNI_intMethod
+  (JNIEnv *env, jobject thisObj, jint n) {
+	return n*n;
+}
+
+/*
+ * Class:     java_exercises7_2_1_HelloJNI
+ * Method:    booleanMethod
+ * Signature: (Z)Z
+ */
+JNIEXPORT jboolean JNICALL Java_java_1exercises7_12_11_HelloJNI_booleanMethod
+  (JNIEnv *env, jobject thisObj, jboolean bool) {
+	return !bool;
+}
+
+/*
+ * Class:     java_exercises7_2_1_HelloJNI
+ * Method:    stringMethod
+ * Signature: (Ljava/lang/String;)Ljava/lang/String;
+ */
+JNIEXPORT jstring JNICALL Java_java_1exercises7_12_11_HelloJNI_stringMethod
+  (JNIEnv *env, jobject thisObj, jstring text) {
+	// Step 1: Convert the JNI String (jstring) into C-String (char*)
+	char *inCStr = (char*)(*env)->GetStringUTFChars(env, text, NULL);
+	if (NULL == inCStr) return NULL;
+
+	// Step 2: Perform its intended operations
+	printf("In C, the received string is: %s\n", inCStr);
+	inCStr[0]++;
+	jstring returnToken=(*env)->NewStringUTF(env, inCStr);
+	(*env)->ReleaseStringUTFChars(env, text, inCStr);  // release resources
+	return returnToken;
+}
+

jni/makefile

@@ -5,8 +5,9 @@ JAVA_HOME=C:\Program Files (x86)\Java\jdk1.8.0_131
 # Define a virtual path for .class in the bin directory
 vpath %.class $(CLASS_PATH)
 
-all : hello.dll
+all : hello.dll java_exercises7_2_1_HelloJNI.dll
 
+# Targets for java_exercises_7_1_1
 # $@ matches the target, $< matches the first dependancy
 hello.dll : HelloJNI.o
 	gcc -Wl,--add-stdcall-alias -shared -o $@ $<
@@ -18,6 +19,18 @@ HelloJNI.o : HelloJNI.c HelloJNI.h
 # $* matches the target filename without the extension
 HelloJNI.h : java_exercises7_1_1/HelloJNI.class
 	javah -o HelloJNI.h -classpath $(CLASS_PATH) java_exercises7_1_1.$*
+	
+# Targets for java_exercises_7_2_1	
+# $@ matches the target, $< matches the first dependancy
+java_exercises7_2_1_HelloJNI.dll : java_exercises7_2_1_HelloJNI.o
+	gcc -Wl,--add-stdcall-alias -shared -o $@ $<
+
+# $@ matches the target, $< matches the first dependancy
+java_exercises7_2_1_HelloJNI.o : java_exercises7_2_1_HelloJNI.c java_exercises7_2_1_HelloJNI.h
+	gcc -I"$(JAVA_HOME)\include" -I"$(JAVA_HOME)\include\win32" -c $< -o $@
+	
+java_exercises7_2_1_HelloJNI.h : java_exercises7_2_1/HelloJNI.class
+	javah -classpath $(CLASS_PATH) java_exercises7_2_1.HelloJNI
 
 clean :
-	rm HelloJNI.h HelloJNI.o hello.dll
\ No newline at end of file
+	rm HelloJNI.h HelloJNI.o hello.dll java_exercises7_2_1_HelloJNI.dll java_exercises7_2_1_HelloJNI.h java_exercises7_2_1_HelloJNI.o
\ No newline at end of file

src/java_exercises7_2_1/HelloJNI.java

+package java_exercises7_2_1;
+
+public class HelloJNI {
+	static {
+		System.loadLibrary("java_exercises7_2_1_HelloJNI"); // Load native library at runtime
+	}
+
+	// Declare a native method sayHello() that receives nothing and returns void
+	private native void sayHello();
+	public native int intMethod(int n);
+	public native boolean booleanMethod(boolean bool);
+	public native String stringMethod(String text);
+	
+	// Test Driver
+	public static void main(String[] args) {
+		HelloJNI helloJNI=new HelloJNI();
+		System.out.println("returned native nr: "+helloJNI.intMethod(2));
+		System.out.println("Returned boolean value: "+helloJNI.booleanMethod(true));
+		System.out.println("Returned string value: "+helloJNI.stringMethod("Test String"));
+	}
+}