create java library that don't display code

I want to create a java library that contains the view, adapter, SQLite, libraries and etc...
but I want the user can't access my library's code.
Actually see an interface of method names just for calling.
how can I do it?

There is no simple, robust way to prevent decompilation of Java classes. However, there are many 'obfuscator' tools for Java that come pretty close in practice.

There is no way to fully protect your source code, especially in Java. You can just make it hard for others to get to your source code.

First method: One major technique is code obfuscation using tools like Proguard. You can enable it by adding the attribute minifyEnabled true to your gradle:

buildTypes {
    release {
        minifyEnabled true
        proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
    }
}

Using this technique, you have to exclude the classes to which user needs to interact. In the proguard config file:

-keep class com.example.myapp.ThisParticularClass

Second method: Another technique that you can use is adding a bit of C/C++ code to your library. You can do some specific tasks like building Strings, special characters, storing keys and numbers in a C/C++ class and then in your java, call those classes.

Third method: While it seems stupid, but it really works. A lot of programmers who decompile your code are not serious enough to spend a lot of time understanding your code. So you can add extra boilerplate code to your project/library by using interfaces, intermediate methods, extra calls and a bunch of other innovative methods.