How to hide API URL and parameters in Android APP?

Hide Url in Environmental variables,BuildConfig and Android Studio

One simple way to avoid this bad practice is to store your values
inside an environmental variable, so only your machine knows it, then
read this values in some way and inject them in your code at build
time. Let’s see how to do that using Android Studio, Gradle, and
BuildConfig.

First, we need to create these environmental vars. In Linux and Mac,
create or edit the file ~/.gradle/gradle.properties (pay attention to
the actual Gradle User Home directory position) and add some values:

WEBServiceBaseURL="http://192.168.2.102:2323/"
WEBServiceBaseSMSURL="https://www.example.com/"

Second, in your module’s build.gradle file, add these lines

//Add these lines
def Base_URL = '"' + WEBServiceBaseURL + '"' ?: '"Define BASE URL"';
def SMS_Base_URL = '"' + WEBServiceBaseSMSURL + '"' ?: '"Define SMS BASE URL"';

android.buildTypes.each { type ->
    type.buildConfigField 'String', 'Base_URL', WEBServiceBaseURL
    type.buildConfigField 'String', 'SMS_Base_URL', WEBServiceBaseSMSURL
}

Use in Java File Like

BuildConfig.Base_URL it will return URL String

  public static Retrofit getClient() {
        if (retrofit==null) {
            retrofit =new Retrofit.Builder()
                    .baseUrl(BuildConfig.Base_URL)
                    .addConverterFactory(GsonConverterFactory.create())
                    .build();
        }
        return retrofit;
    }