activity_main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 android:id="@+id/activity_main"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:orientation="vertical"
 android:padding="16dp">

 <LinearLayout
 android:orientation="horizontal"
 android:layout_width="fill_parent"
 android:layout_height="wrap_content">


 <Button
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:onClick="sendMessage"
 android:id="@+id/button1"
 android:text=" " />

 <Button
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:onClick="sendMessage"
 android:id="@+id/button2"
 android:text=" " />

 <Button
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:onClick="sendMessage"
 android:id="@+id/button3"
 android:text=" " />
 </LinearLayout>
 <LinearLayout
 android:orientation="horizontal"
 android:layout_width="fill_parent"
 android:layout_height="wrap_content">


 <Button
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:onClick="sendMessage"
 android:id="@+id/button4"
 android:text=" " />

 <Button
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:onClick="sendMessage"
 android:id="@+id/button5"
 android:text=" " />

 <Button
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:onClick="sendMessage"
 android:id="@+id/button6"
 android:text=" " />
 </LinearLayout>
 <LinearLayout
 android:orientation="horizontal"
 android:layout_width="fill_parent"
 android:layout_height="wrap_content">


 <Button
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:onClick="sendMessage"
 android:id="@+id/button7"
 android:text=" " />

 <Button
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:onClick="sendMessage"
 android:id="@+id/button8"
 android:text=" " />

 <Button
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:onClick="sendMessage"
 android:id="@+id/button9"
 android:text=" " />
 </LinearLayout>
</LinearLayout>

MainActivity

package com.example.myapplication;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;

import android.view.View;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Button;


public class MainActivity extends AppCompatActivity {
 int click = 0;
 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);
 }


 ///////////////////
 public void sendMessage(View v) {
 Button b1 = (Button) findViewById(R.id.button1);
 Button b2 = (Button) findViewById(R.id.button2);
 Button b3 = (Button) findViewById(R.id.button3);
 Button b4 = (Button) findViewById(R.id.button4);
 Button b5 = (Button) findViewById(R.id.button5);
 Button b6 = (Button) findViewById(R.id.button6);
 Button b7 = (Button) findViewById(R.id.button7);
 Button b8 = (Button) findViewById(R.id.button8);
 Button b9 = (Button) findViewById(R.id.button9);
 String buttonText = "";
 if (click == 0) {
 click = 1;
 }
 else
 {
 click = 0;
 }

 switch (v.getId()) {

 case R.id.button1:

 buttonText = b1.getText().toString();
 if (buttonText.equals(" ") && click == 1) b1.setText("X");
 if (buttonText.equals(" ") && click == 0) b1.setText("O");
 break;
 case R.id.button2:
 buttonText = b2.getText().toString();
 if (buttonText.equals(" ") && click == 1) b2.setText("X");
 if (buttonText.equals(" ") && click == 0) b2.setText("O");
 break;
 case R.id.button3:
 buttonText = b3.getText().toString();
 if (buttonText.equals(" ") && click == 1) b3.setText("X");
 if (buttonText.equals(" ") && click == 0) b3.setText("O");
 break;
 case R.id.button4:
 buttonText = b4.getText().toString();
 if (buttonText.equals(" ") && click == 1) b4.setText("X");
 if (buttonText.equals(" ") && click == 0) b4.setText("O");
 break;
 case R.id.button5:
 buttonText = b5.getText().toString();
 if (buttonText.equals(" ") && click == 1) b5.setText("X");
 if (buttonText.equals(" ") && click == 0) b5.setText("O");
 break;
 case R.id.button6:
 buttonText = b6.getText().toString();
 if (buttonText.equals(" ") && click == 1) b6.setText("X");
 if (buttonText.equals(" ") && click == 0) b6.setText("O");
 break;
 case R.id.button7:
 buttonText = b7.getText().toString();
 if (buttonText.equals(" ") && click == 1) b7.setText("X");
 if (buttonText.equals(" ") && click == 0) b7.setText("O");

 break;
 case R.id.button8:
 buttonText = b8.getText().toString();
 if (buttonText.equals(" ") && click == 1) b8.setText("X");
 if (buttonText.equals(" ") && click == 0) b8.setText("O");
 break;
 case R.id.button9:
 buttonText = b9.getText().toString();
 if (buttonText.equals(" ") && click == 1) b9.setText("X");
 if (buttonText.equals(" ") && click == 0) b9.setText("O");
 break;


 }

 }

 //////////////
}