RadioGroup

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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:id="@+id/main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".RadioGroupActivity">

    <RadioGroup
        android:layout_marginTop="30dp"
        android:id="@+id/rg"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintTop_toTopOf="parent">

        <RadioButton
            android:id="@+id/rb_bd"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:checked="true"
            android:text="百度" />

        <RadioButton
            android:id="@+id/rb_gg"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="google" />

        <RadioButton
            android:id="@+id/rb_360"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="360" />

        <RadioButton
            android:id="@+id/rb_sg"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="搜狗" />
    </RadioGroup>

    <Button
        android:id="@+id/btn_settings"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="设置默认搜索引擎"
        app:layout_constraintTop_toBottomOf="@+id/rg"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        />
</androidx.constraintlayout.widget.ConstraintLayout>

package com.example.testjava1;

import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.RadioGroup;
import android.widget.Toast;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;

public class RadioGroupActivity extends AppCompatActivity {

    private static final String TAG = "RadioGroupActivity";

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

        RadioGroup rg = findViewById(R.id.rg);

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

                Toast toast = Toast.makeText(RadioGroupActivity.this, getUrl(checkedId), Toast.LENGTH_SHORT);

                toast.show();

                Log.e(TAG, "onCheckedChanged: " + group.toString());
            }
        });

        Button btn = findViewById(R.id.btn_settings);

        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                int id = rg.getCheckedRadioButtonId();

                Toast toast = Toast.makeText(RadioGroupActivity.this, "已将搜索引擎设置为：" + getUrl(id), Toast.LENGTH_SHORT);

                toast.show();

                Log.e(TAG, "onCheckedChanged: " + v.toString());
            }
        });
    }

    static private String getUrl(int id) {
        String url = "http://baidu.com";
        if (id == R.id.rb_bd) {
            url = "http://baidu.com";
        } else if (id == R.id.rb_gg) {
            url = "http://google.com";
        } else if (id == R.id.rb_360) {
            url = "http://360.com";
        } else {
            url = "http://sogou.com";
        }
        return url;
    }
}