How to use Intent.ACTION.ANSWER?

Question

I'm new to android development and trying to make an app with 2 buttons, one calls a specific number and the other just answers the phone when being called. Except I don't really know what to define in the ACTION_ANSWER area.. Thanks in advance!

My MainActivity.java

import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;


public class MainActivity extends ActionBarActivity {

    private Button button1;
    private Button button2;

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

        button1 = (Button) findViewById(R.id.buttonCall);

        button1.setOnClickListener(new OnClickListener() {
            public void onClick(View arg0) {
                Intent callIntent = new Intent(Intent.ACTION_CALL);
                callIntent.setData(Uri.parse("tel:0634834906"));
                startActivity(callIntent);
            }
        });

        button2 = (Button) findViewById(R.id.buttonAnswer);
        button2.setOnClickListener(new OnClickListener() {
            public void onClick(View arg0) {
                Intent answerIntent = new Intent(Intent.ACTION_ANSWER);

            }
        });
    }
}