Steps:
1. Convert APK to JAR
2. Convert JAR to source code

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Details:

Source code:

package com.programmerworld.testappforapktosourecodeconversion;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.view.View;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    private TextView textView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        textView = findViewById(R.id.textView);
    }
    
    public void buttonSet(View view){
        textView.setText("This is programmer world App");
    }
    
    public void buttonClear(View view){
        textView.setText("Hello Programmer World!!!");
    }
}

Screenshots:

C:\Work\dex-tools-2.1>d2j-dex2jar -h
d2j-dex2jar -- convert dex to jar
usage: d2j-dex2jar [options] <file0> [file1 ... fileN]
options:
 --skip-exceptions            skip-exceptions
 -d,--debug-info              translate debug info
 -e,--exception-file <file>   detail exception file, default is $current_dir/[fi
                              le-name]-error.zip
 -f,--force                   force overwrite
 -h,--help                    Print this help message
 -n,--not-handle-exception    not handle any exceptions thrown by dex2jar
 -nc,--no-code
 -o,--output <out-jar-file>   output .jar file, default is $current_dir/[file-na
                              me]-dex2jar.jar
 -os,--optmize-synchronized   optimize-synchronized
 -p,--print-ir                print ir to System.out
 -r,--reuse-reg               reuse register while generate java .class file
 -s                           same with --topological-sort/-ts
 -ts,--topological-sort       sort block by topological, that will generate more
                               readable code, default enabled
version: reader-2.1, translator-2.1, ir-2.1

C:\Work\dex-tools-2.1>d2j-dex2jar apk\app-debug.apk
dex2jar apk\app-debug.apk -> .\app-debug-dex2jar.jar

C:\Work\dex-tools-2.1>

Links of Tools: used in this demo:

Dex2Jar:

https://drive.google.com/file/d/1BaFRPTbhDD7BlPnmToq9AJxB0IAWpwmn/view?usp=drive_link

https://github.com/pxb1988/dex2jar/releases
https://sourceforge.net/projects/dex2jar/files/

JD-GUI/ Java decompiler:

https://drive.google.com/file/d/1eZOX6USPyy4Uq6YSXPFZN43OiF5ze75J/view?usp=drive_link

http://java-decompiler.github.io/