Uses of Interfaces in android Development.

It is a collection of constants, methods(abstract, static and default) and nested types.

• All the methods of the interface needs to be defined in the class.
• Interface is like a Class.
  Class describes the behaviors of implements.

Difference From Class

• Can not instantiate an interface and can't contain instance fields.
• An interface has no constructors.
• All of the methods in an interface are abstract.
• All the fields that can appear in an interface must be declared both static and final.
• An interface can extend multiple interfaces.

The interface keyword is used to declare an interface.

public interface AdapterCallBackListener {
    void onRowClick(String searchText);
}
public interface OnFragmentInteractionListener {
    void onFragmentInteraction();
}

A class uses the implements keyword to implement an interface.

public class CustomActivity extends AppCompatActivity
       implements CustomAdapter.AdapterCallBackListener,
        CustomFragment.OnFragmentInteractionListener{
    void onRowClick(String searchText {
       System.out.println("Today’s SearchText" + searchText);
    }
    void onFragmentInteraction() {
       System.out.println("On Fragment Interact");
    }
}

Class uses Interface as function.

adapter.setCallBackListner(new CustomAdapter.AdapterCallBackListener() {
    @Override
    public void onRowClick(String searchText) {
        Toast.makeText(CustomActivity.this,
                searchText, Toast.LENGTH_SHORT).show();

    }
});
//setCallBackListner method declared in CustomAdapter.

Insert value in interfaces.

public class CustomAdapter {

    private AdapterCallBackListener callBackListener;
    ................
    ................
  
    public void setCallBackListner(AdapterCallBackListener callBackListener) {
        this.callBackListener = callBackListener;
    }
    searchRow.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                callBackListener.onRowClick(searchText);
            }
        });

    public interface AdapterCallBackListener{
        void onRowClick(String searchText);
    }
}