[Android] 버튼눌렀을때 Text 변하게 하기

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <!-- note
    orientation : LinearLayout에서 세로로 텍스트나열
    -->


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

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

</LinearLayout>

 

 

MainActivity.java

package com.example.study_1;

import androidx.appcompat.app.AppCompatActivity;

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

public class MainActivity extends AppCompatActivity {

    EditText et_id;
    Button btn_test;

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



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

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

    }
}