MainActivity.java

package br.com.fiap.primeiroaplicativo;

import android.support.annotation.NonNull;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.CheckBox;
import android.widget.CompoundButton;
import android.widget.EditText;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.widget.RatingBar;
import android.widget.SeekBar;
import android.widget.Spinner;
import android.widget.Switch;
import android.widget.Toast;
import android.widget.ToggleButton;

public class MainActivity extends AppCompatActivity {

    private EditText campo1;
    private EditText     campo2;
    private RatingBar    classificador;
    private SeekBar      volume;
    private CheckBox     caixa;
    private Switch       tomada;
    private ToggleButton ligaDesliga;
    private RadioGroup   grupoDeRadios;
    private Spinner      listaDeDados;
    private Button       botao;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        campo1 = findViewById(R.id.editText);
        campo2 = findViewById(R.id.editText2);
        classificador = findViewById(R.id.ratingBar);
        volume = findViewById(R.id.seekBar);
        caixa = findViewById(R.id.checkBox);
        tomada = findViewById(R.id.switch1);
        ligaDesliga = findViewById(R.id.toggleButton);
        grupoDeRadios = findViewById(R.id.radioGroup);
        listaDeDados = findViewById(R.id.spinner);
        botao = findViewById(R.id.button);

        caixa.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
                String texto = getString(isChecked);

                Toast.makeText(MainActivity.this, texto, Toast.LENGTH_SHORT).show();
            }

            @NonNull
            private String getString(boolean isChecked) {
                String texto = "";

                texto = isChecked ? "Marcado" : "Desmarcado";
                return texto;
            }
        });

        botao.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Toast.makeText(MainActivity.this,
                        "Minha primeira msg. Uhu!",
                        Toast.LENGTH_SHORT).show();
            }
        });

        tomada.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
                String texto = "";

                texto = isChecked ? "Ligado" : "Desligado";

                Toast.makeText(MainActivity.this,
                        texto,
                        Toast.LENGTH_SHORT).show();
            }
        });

        grupoDeRadios.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(RadioGroup group, int checkedId) {

                RadioButton radioSelect = findViewById(checkedId);

                Toast.makeText(MainActivity.this,
                        radioSelect.getText(),
                        Toast.LENGTH_SHORT).show();
            }
        });
    }
}