Select only one radio button

Question

I want to select just one radio button at a time, but after selecting one of them when I click on the other button they both are selected, what can I do to solve this problem.

My MainActivity.java code is

public class MainActivity extends AppCompatActivity {

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

}

public void onClick(View view) {
    TextView text=(TextView)findViewById(R.id.txt1);
    text.setText("Wrong Answer");
}

public void onClick1(View view) {
    TextView text=(TextView)findViewById(R.id.txt1);
    text.setText("You are Right");
}
}

Answer 1

RadioButton should be the direct child of RadioGroup, Otherwise grouping does not work.

<RadioGroup
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:id="@+id/radioGroup">
    <RadioButton
        android:layout_width="0dp"
        android:layout_weight="50"
        android:layout_height="wrap_content"
        android:text="Debit"
        android:id="@+id/rDebit"
        android:checked="false"
         />

    <RadioButton
        android:layout_width="0dp"
        android:layout_weight="50"
        android:layout_height="wrap_content"
        android:text="Credit"
        android:id="@+id/rCredit"
        android:checked="false" />

</RadioGroup>

And in java file

RadioGroup radioGroup;

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

do something

 if (radioGroup.getCheckedRadioButtonId() == R.id.rCredit)
{
// do something
}

Answer 2

The accepted answer was deleted and cannot be undeleted. Probably because it was barely more than a link to an external site. So here is a more detailed version:

You need to group the radio buttons within the same RadioGroup in your layout file.

See here: https://developer.android.com/guide/topics/ui/controls/radiobutton.html

Applied to your problem this could look like this:

<RadioGroup 
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content">

    <RadioButton
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="onClick"
        android:text="Dennis Ritchie" />

    <RadioButton
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="onClick1"
        android:text="James Gosling" />
</RadioGroup>