EditText & Button 하는 법

MainActivity
package com.shb.mycalculator;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

public class MainActivity extends AppCompatActivity {

EditText et_test;
Button btn_test;

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

    et_test = findViewById(R.id.et_test);
    btn_test = findViewById(R.id.btn_test);

    btn_test.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            et_test.setText("홍길동");
        }
    });


}

}

Main_xml

<EditText
    android:id="@+id/et_test"
    android:layout_width="300dp"
    android:layout_height="wrap_content"
    android:hint="아이디를 입력하시오" />

<Button
    android:id="@+id/btn_test"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="버튼"/>