Android Studio – Attempt to invoke virtual method 'void android.widget.TextView.setTypeface(android.graphics.Typeface)' on a null object reference in java

I checked the code you provided and found that the java.lang.NullPointerException problem you were experiencing probably did not occur when the GameActivity.java is opened for first time. That problem pops up when the answer given is wrong.

Do I understand exactly?

If so, then the reason is here:

private void doValidate (){
....
    linearLayout.removeAllViews ();
....
}

In above code, you’ve removed all child views and then you have called

for (String key : keys) {
    addView(linearLayout, key, editText);
}

The editText you have referenced here, that has also been removed.

So, as expected, java.lang.NullPointerException is coming up here:

textQuestion = (TextView) findViewById(R.id.textQuestion);
textScreen = (TextView) findViewById(R.id.textScreen);
textTitle = (TextView) findViewById(R.id.textTitle);

textQuestion.setTypeface(typeface);
textScreen.setTypeface(typeface);
textTitle.setTypeface(typeface);
editText.setTypeface(typeface);

As textQuestion, textScreen, textTitle and editText don’t exists anymore.

What should be done then?

In fact, the real problem is elsewhere. And that is you have mistakenly named wrong LinearLayout as R.id.layoutParent. Just add the below line to last LinearLayout instead of root LinearLayout

android:id="@+id/layoutParent"

Just like below:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    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"
    android:orientation="vertical"
    android:background="@drawable/bgapp"
    tools:context=".GameActivity">

    <TextView
        android:id="@+id/textScreen"
        android:layout_marginTop="40dp"
        android:layout_gravity="center"
        android:textColor="#FFF"
        android:textSize="22sp"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="In Fight Battle" />

    <LinearLayout
        android:layout_marginTop="50dp"
        android:layout_gravity="center"
        android:background="@drawable/bgquestion"
        android:orientation="vertical"
        android:gravity="center"
        android:layout_width="290dp"
        android:layout_height="150dp">

        <TextView
            android:textAlignment="center"
            android:id="@+id/textQuestion"
            android:textColor="#332FA2"
            android:textSize="26sp"
            android:layout_width="220dp"
            android:lineSpacingExtra="6dp"
            android:layout_height="wrap_content"
            android:text="Guess Animals in English language" />

    </LinearLayout>

    <EditText
        android:id="@+id/editText"
        android:layout_marginBottom="70dp"
        android:padding="10dp"
        android:clickable="false"
        android:focusable="false"
        android:textColor="#332FA2"
        android:textSize="32sp"
        android:gravity="center"
        android:layout_gravity="center"
        android:layout_marginTop="70dp"
        android:background="@drawable/bgpurple"
        android:layout_width="200dp"
        android:layout_height="80dp" />

    <TextView
        android:id="@+id/textTitle"
        android:text="Ammo"
        android:textSize="24sp"
        android:textColor="#FFF"
        android:layout_marginRight="28dp"
        android:layout_marginLeft="28dp"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginBottom="16dp"
        />


    <LinearLayout
        android:id="@+id/layoutParent"
        android:layout_marginLeft="24dp"
        android:layout_marginRight="24dp"
        android:orientation="horizontal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">


    </LinearLayout>

</LinearLayout>

One more thing that you should take care about.

Every time you call addView, TypeFace will be generated from asset and will be assigned to textviews again and again.

You should create class wise variables that can be used later.

Your GameActivity.java should be like below:

import android.annotation.SuppressLint;
import android.content.Intent;
import android.graphics.Typeface;
import android.os.Bundle;
import android.view.Gravity;
import android.view.View;
import android.view.animation.Animation;
import android.view.animation.AnimationUtils;
import android.widget.EditText;
import android.widget.LinearLayout;
import android.widget.TextView;
import android.widget.Toast;

import androidx.appcompat.app.AppCompatActivity;

import java.util.Random;

public class GameActivity extends AppCompatActivity {
    private int presCounter = 0;
    private int maxPresCounter = 4;
    private String[] keys = {"R", "I", "B", "D", "X"};
    private String textAnswer = "BIRD";
    private TextView textScreen, textQuestion, textTitle;
    private Animation smallbigforth;
        
    // Create variables here

    private Typeface typeface;
    private EditText editText;
    private LinearLayout linearLayout;
    private LinearLayout.LayoutParams linearLayoutParams;

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

        //--------------------------------------------------------------------------------------------
        // Get typeface from asset
        // then assign it to desired views

        typeface = Typeface.createFromAsset(getAssets(), "fonts/FredokaOneRegular.ttf");

        // find views and save it for later references

        textQuestion = findViewById(R.id.textQuestion);
        textScreen = findViewById(R.id.textScreen);
        textTitle = findViewById(R.id.textTitle);
        editText = findViewById(R.id.editText);
        linearLayout = findViewById(R.id.layoutParent);

        
        // set typeface of another views

        textQuestion.setTypeface(typeface);
        textScreen.setTypeface(typeface);
        textTitle.setTypeface(typeface);
        editText.setTypeface(typeface);
        
        // You should initiate linearLayoutParams here
        // it will be used later

        linearLayoutParams = new LinearLayout.LayoutParams(
                LinearLayout.LayoutParams.WRAP_CONTENT,
                LinearLayout.LayoutParams.WRAP_CONTENT,
                );

        linearLayoutParams.rightMargin = 30;
        //--------------------------------------------------------------------------------------------

        smallbigforth = AnimationUtils.loadAnimation(this, R.anim.smallbigforth);

        keys = shuffleArray(keys);

        for (String key : keys) {
            addView(linearLayout, key);
        }

        maxPresCounter = 4;
    }


    private String[] shuffleArray(String[] ar) {
        Random rnd = new Random();
        for (int i = ar.length - 1; i > 0; i--) {
            int index = rnd.nextInt(i + 1);
            String a = ar[index];
            ar[index] = ar[i];
            ar[i] = a;
        }
        return ar;
    }


    private void addView(LinearLayout viewParent, final String text) {


        final TextView textView = new TextView(this);

        // set LayoutParams of newly created textView

        textView.setLayoutParams(linearLayoutParams);
        textView.setBackground(this.getResources().getDrawable(R.drawable.bgpink));
        textView.setTextColor(this.getResources().getColor(R.color.colorPurple));
        textView.setGravity(Gravity.CENTER);
        textView.setText(text);
        textView.setClickable(true);
        textView.setFocusable(true);
        textView.setTextSize(32);

        // set typeface of newly created textView
        
        textView.setTypeface(typeface);

        textView.setOnClickListener(new View.OnClickListener() {

            @SuppressLint("SetTextI18n")
            @Override
            public void onClick(View v) {
                if (presCounter < maxPresCounter) {
                    if (presCounter == 0)
                        editText.setText("");

                    editText.setText(editText.getText().toString() + text);
                    textView.startAnimation(smallbigforth);
                    textView.animate().alpha(0).setDuration(300);
                    presCounter++;

                    if (presCounter == maxPresCounter)
                        doValidate();
                }
            }
        });


        viewParent.addView(textView);


    }


    private void doValidate() {
        presCounter = 0;

        if (editText.getText().toString().equals(textAnswer)) {
            //Toast.makeText(MainActivity.this, "Correct", Toast.LENGTH_SHORT).show();

            Intent a = new Intent(GameActivity.this, BossAct.class);
            startActivity(a);

            editText.setText("");
        } else {
            Toast.makeText(GameActivity.this, "Wrong", Toast.LENGTH_SHORT).show();
            editText.setText("");
        }

        keys = shuffleArray(keys);
        linearLayout.removeAllViews();
        for (String key : keys) {
            addView(linearLayout, key);
        }

    }

}

And that’ all I know. Hope this will help.