activity_main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent" 
    android:orientation="vertical">

    <TextView
        android:id="@+id/xz"
 

        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/sex" />
    <!--單選按鈕RadioButton 必須放到RadioGroup中-->
    <RadioGroup
        android:id="@+id/sex"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
 
 
        android:orientation="horizontal">

        <RadioButton
            android:id="@+id/male"
            android:layout_width="match_parent"
            android:layout_height="match_parent" 
            android:text="@string/male"/>
         <RadioButton
            android:id="@+id/female"
 

            android:layout_width="match_parent"
            android:layout_height="match_parent" 
            android:text="@string/female"/>
    </RadioGroup>
</LinearLayout>

MainActivity.java

import android.app.Activity;
import android.os.Bundle;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.widget.RadioGroup.OnCheckedChangeListener;
import android.widget.TextView;

public class MainActivity extends Activity implements OnCheckedChangeListener{

    private  TextView xz;
    private RadioGroup sex;
    private RadioButton male;
    private RadioButton female;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        xz=(TextView) findViewById(R.id.xz);
        sex=(RadioGroup) findViewById(R.id.sex);
        male=(RadioButton) findViewById(R.id.male);
        female=(RadioButton) findViewById(R.id.female);
        sex.setOnCheckedChangeListener(MainActivity.this);
    }
    @Override
    public void onCheckedChanged(RadioGroup group, int checkedId) {
        String result = null;
        if (male.getId()==checkedId) {
            result=male.getText().toString();
        }else if(female.getId()==checkedId){
            result=female.getText().toString();
        }
        xz.setText("您選擇的性別是："+result);  
    }

}