How could I include new jar file on android?

I am trying to embed the ads of AppBucks into the android app but have no idea how to do it

According to the website, I should place the MobileSDK.jar into the android-build/lib
But the compiler would complaint that “package com.appbucks.sdk does not exist” when
I include the package

appBucksAdv.java

Code:

---

package adv;
 
    import com.appbucks.sdk.AppBucksAPI;
 
    import org.qtproject.qt5.android.bindings.QtApplication;
    import org.qtproject.qt5.android.bindings.QtActivity;
 
    import android.os.Bundle;
 
    public class appBucksAdv extends QtActivity
    {
        private static appBucksAdv m_instance;
 
        public appBucksAdv()
        {
            m_instance = this;
        }
 
        @Override
        public void onCreate(Bundle savedInstanceState)
        {
          super.onCreate(savedInstanceState);
 
          AppBucksAPI.initialize(this, "chartUnitConverter",
          1, "4444", false, null, null);
        }
    }

---

source codes :
https://github.com/stereomatchingkis...er/androidTest

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Added after 6 minutes:

Find out the answer, I should put at the inside of the android folder.
Create a libs library and drop the MobileSDK.jar into it but not the folder after builded.