Memory Letter Game

letterFipGame.java

package com.example.letterflipgame;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.view.View;
import android.widget.Button;

import java.util.Random;

public class MainActivity extends AppCompatActivity {
    String[]letters = new String[]{"A","A","B","B","C","C","D","D"};
    Button buttonA,buttonA1,buttonB,buttonB1,buttonC,buttonC1,buttonD,buttonD1,reset1;
    boolean bandera1 = false, bandera2 = false;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        init();
    }
    public void init(){
        buttonA = (Button)findViewById(R.id.button4);
        buttonB = (Button)findViewById(R.id.button);
        buttonC = (Button)findViewById(R.id.button2);
        buttonD = (Button)findViewById(R.id.button3);
        buttonA1 = (Button)findViewById(R.id.button9);
        buttonB1 = (Button)findViewById(R.id.button11);
        buttonC1 = (Button)findViewById(R.id.button12);
        buttonD1 = (Button)findViewById(R.id.button13);
        reset1 = (Button)findViewById(R.id.reset1);
        buttonA.setVisibility(View.VISIBLE);
        buttonA1.setVisibility(View.VISIBLE);
        buttonB.setVisibility(View.VISIBLE);
        buttonB1.setVisibility(View.VISIBLE);
        buttonC.setVisibility(View.VISIBLE);
        buttonC1.setVisibility(View.VISIBLE);
        buttonD.setVisibility(View.VISIBLE);
        buttonD1.setVisibility(View.VISIBLE);
        letters = shuffleArray(letters);
        buttonA.setText(letters[0]);
        buttonB.setText(letters[1]);
        buttonC.setText(letters[2]);
        buttonD.setText(letters[3]);
        buttonA1.setText(letters[4]);
        buttonB1.setText(letters[5]);
        buttonC1.setText(letters[6]);
        buttonD1.setText(letters[7]);
    }


    public void b1(View view){
        buttonA.setVisibility(View.INVISIBLE);
    }
    public void b2(View view){
        buttonB.setVisibility(View.INVISIBLE);
    }
    public void b3(View view){
        buttonC.setVisibility(View.INVISIBLE);
    }
    public void b4(View view){
        buttonD.setVisibility(View.INVISIBLE);
    }
    public void b5(View view){
        buttonA1.setVisibility(View.INVISIBLE);
    }
    public void b6(View view){
        buttonB1.setVisibility(View.INVISIBLE);
    }
    public void b7(View view){
        buttonC1.setVisibility(View.INVISIBLE);
    }
    public void b8(View view){
        buttonD1.setVisibility(View.INVISIBLE);
    }



    public void reset(View view){
        init();
    }
    private static String[] shuffleArray(String[]array){
        int index;
        String temp;
        Random random = new Random();
        for (int i = array.length -1; i > 0 ; i--) {
            index = random.nextInt(i + 1);
            temp = array[index];
            array[index] = array[i];
            array[i] = temp;
        }
        return array;
    }
}

LetterFlipGame.xml

<?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:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">


    <Button
        android:id="@+id/button4"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="76dp"
        android:onClick="b1"
        android:text="@string/button1"
        android:visibility="visible"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.445" />

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="196dp"
        android:onClick="b2"
        android:text="@string/button2"
        android:visibility="visible"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.445" />

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="76dp"
        android:text="@string/button3"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.56"
        android:onClick="b3"/>

    <Button
        android:id="@+id/button3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="196dp"
        android:onClick="b4"
        android:text="@string/button4"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.56" />

    <Button
        android:id="@+id/button9"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="76dp"
        android:text="@string/button5"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.669"
        android:onClick="b5"/>

    <Button
        android:id="@+id/button11"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="196dp"
        android:text="@string/button6"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.669"
        android:onClick="b6"/>

    <Button
        android:id="@+id/button12"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="76dp"
        android:text="@string/button7"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.765"
        android:onClick="b7"/>

    <Button
        android:id="@+id/button13"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="196dp"
        android:text="@string/button8"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.765"
        android:onClick="b8"/>

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="80dp"
        android:text="@string/resetButton"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.82"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        android:onClick="reset"
        android:id="@+id/reset1"/>

</androidx.constraintlayout.widget.ConstraintLayout>