Example of calling Java methods through the JNI, in ARM Assembly, on Android

.data
java_method_name:
  .ascii "revealTheSecret\0"
java_method_signature:
  .ascii "(Ljava/lang/String;)V\0"

// Our UTF16-LE encoded secret message
secret:
  .hword 55357, 56892, 85, 110, 32, 99, 104, 97, 116, 10
  .hword 55357, 56377, 12495, 12512, 12473, 12479, 12540, 10
  .hword 55357, 56360, 27193, 29066, 10
  .hword 55357, 56445, 65, 110, 32, 97, 108, 105, 101, 110, 10
secret_len = . - secret 
secret_len = secret_len / 2  // 2 bytes per character

.text
.align 2
.globl Java_adventurers_decyphering_secrets_decyphapp_DecypherActivity_decypherArcaneSecrets
.type Java_adventurers_decyphering_secrets_decyphapp_DecypherActivity_decypherArcaneSecrets, %function
Java_adventurers_decyphering_secrets_decyphapp_DecypherActivity_decypherArcaneSecrets:
  push {r4-r7, lr} // Prologue. We will use r4, r5, r6, r7
  
  // Passed parameters - r0 : *_JNIEnv, r1 : thisObject

  mov r4, r0   // r4 : Backup of *JNIEnv as we'll use it very often
  mov r5, r1   // r5 : Backup of thisObject as we'll invoke methods on it
  ldr r6, [r0] // r6 : Backup of *_JNINativeInterface, located at *_JNIEnv,
               //      since we'll also use it a lot
  
  // Preparing to call NewString(*_JNIEnv : r0, *string_characters : r1, string_length : r2). 
  // *_JNIEnv is already loaded.

  ldr r1, =secret     // r1 : The UTF16-LE characters composing the java.lang.String
  mov r2, #secret_len // r2 : The length of the String
  ldr r3, [r6, #652]  // Get *JNINativeInterface->NewString. +652 is NewString's offset
  blx r3              // secret_string : r0 <- NewString(*_JNIEnv : r0, *string_characters : r1, string_length : r2)
  mov r7, r0          // r7 : secret_string - Keep the returned string for later use
  
  // Calling showText(java.lang.String) through the JNI
  // 
  // First : We need the class of thisObject. We could pass it directly
  // to the procedure but, for learning purposes, we'll use JNI methods
  // to get it.
  
  // Preparing to call GetObjectClass(*_JNIEnv : r0, thisObject : r1)
  mov r0, r4         // r0 : *_JNIEnv
  mov r1, r5         // r1 : thisObject
  ldr r2, [r6, #124] // Get *JNINativeInterface->GetObjectClass (+124)
  blx r2             // jclass : r0 <- GetObjectClass(r0 : *JNIEnv, r1 : thisObject)
  
  // Second : We need the JNI ID of the method we want to call
  // Preparing for GetMethodId(r0 : *JNIEnv, r1 : jclass, r2 : method_name, r3 : method_signature)
  mov r1, r0 // r1 : jclass returned by GetObjectClass
  mov r0, r4 // r0 : *JNIEnv, previously backed up in r4
  ldr r2, =java_method_name      // r2 : The method name
  ldr r3, =java_method_signature // r3 : The method signature
  ldr r8, [r6, #132]             // Get *JNINativeInterface->GetMethodId (+132)
  blx r8     // revealTheSecretID : r0 <- GetMethodId(*_JNIEnv : r0, jclass : r1, method_name : r2, method_signature : r3)
  
  // Finally : Call the method. Since it's a method returning void, we'll use CallVoidMethod.
  // Preparing to call CallVoidMethod(*_JNIEnv : r0, thisObject : r1, revealTheSecretID : r2, secret_string : r3)
  mov r2, r0         // r2 : revealTheSecretID : Backup the ID for later
  mov r1, r5         // r1 : thisObject
  mov r0, r4         // r0 : *_JNIEnv
  mov r3, r7         // r3 : secret_string
  ldr r8, [r6, #244] // Get *_JNINativeInterface->CallVoidMethod (+244). 
  blx r8 // CallVoidMethod(*_JNIEnv : r0, thisObject : r1, revealTheSecretID : r2, the_string : r3)
         // -> revealTheSecret(the_string)
  
  pop {r4-r7, pc} // Restoring the scratch-registers and returning by loading the link-register into the program-counter

package adventurers.decyphering.secrets.decyphapp;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.TextView;

public class DecypherActivity extends AppCompatActivity {

  static { System.loadLibrary("arcane"); }
  native void decypherArcaneSecrets();

  TextView mContentView;

  public void revealTheSecret(String text) {
    mContentView.setText(text);
  }

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.activity_decypher);

    mContentView = (TextView) findViewById(R.id.fullscreen_content);
    decypherArcaneSecrets();
  }
}

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
   xmlns:tools="http://schemas.android.com/tools"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   android:background="#0099cc"
   tools:context="adventurers.decyphering.secrets.decyphapp.DecypherActivity"
  >

  <!-- The primary full-screen view. This can be replaced with whatever view
  is needed to present your content, e.g. VideoView, SurfaceView,
  TextureView, etc. -->
  <TextView
   android:id="@+id/fullscreen_content"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   android:gravity="center"
   android:keepScreenOn="true"
   android:textColor="#33b5e5"
   android:textSize="50sp"
   android:textStyle='bold'
   />

</FrameLayout>

void a(int a, long b, String c, HashMap[] d, boolean e)

package your.package.name;

import java.lang.reflect.Method;
import java.util.HashMap;

import android.util.Log;

public class MethodsHelpers {

  static public HashMap<Class, String> primitive_types_codes;
  static public String LOG_TAG = "MY_APP";

  static {
    primitive_types_codes = new HashMap<Class,String>();
    primitive_types_codes.put(void.class,    "V");
    primitive_types_codes.put(boolean.class, "Z");
    primitive_types_codes.put(byte.class,    "B");
    primitive_types_codes.put(short.class,   "S");
    primitive_types_codes.put(char.class,    "C");
    primitive_types_codes.put(int.class,     "I");
    primitive_types_codes.put(long.class,    "J");
    primitive_types_codes.put(float.class,   "F");
    primitive_types_codes.put(double.class,  "D");
  }

  public static String code_of(final Class class_object) {
    final StringBuilder class_name_builder = new StringBuilder(20);
    Class component_class = class_object;
    while (component_class.isArray()) {
      class_name_builder.append("[");
      component_class = component_class.getComponentType();
    }
    if (component_class.isPrimitive())
      class_name_builder.append(primitive_types_codes.get(component_class));
    else {
      class_name_builder.append("L");
      class_name_builder.append(
        component_class.getCanonicalName().replace(".", "/")
      );
      class_name_builder.append(";");
    }
    return class_name_builder.toString();
  }

  public static void print_methods_descriptors_of(Class analysed_class) {
    StringBuilder descriptor_builder = new StringBuilder(32);
    Method[] methods = analysed_class.getDeclaredMethods();
    for (Method meth : methods) {
      descriptor_builder.append("(");

      for (Class param_class : meth.getParameterTypes())
        descriptor_builder.append(code_of(param_class));

      descriptor_builder.append(")");

      descriptor_builder.append(code_of(meth.getReturnType()));

      Log.d(LOG_TAG,
            String.format("%s\n"+
                          "Name       : %s\n"+
                          "Descriptor : %s\n\n",
                          meth.toString(),
                          meth.getName(),
                          descriptor_builder.toString())
      );

      descriptor_builder.delete(0, descriptor_builder.length());
    }
  }

}

import static your_package_name.MethodHelpers.print_methods_descriptors_of;

...

print_methods_descriptors_of(AnalysedClass.class);