com.example.android.javapractice E/AndroidRuntime: FATAL EXCEPTION: main
                                                                              Process: com.example.android.javapractice, PID: 13735
                                                                              java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.android.javapractice/com.example.android.javapractice.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference

<TextView
    android:id="@+id/test"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Hello World!"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent"
    app:layout_constraintTop_toTopOf="parent" />

<Button
    android:id="@+id/turn_on"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="button"/>

package com.example.android.javapractice;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import java.util.Random;

public class MainActivity extends AppCompatActivity {

TextView test = findViewById(R.id.test);
Button turn = findViewById(R.id.turn_on);
int count = 1;

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

    turn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            keepRoll();
        }
    });
}

public int rollDice(){
    int num = 0;
    int roll;
    Random randomRoll = new Random();
    roll = randomRoll.nextInt(6)+1;
    System.out.println("Roll is:  "+roll);
    num += roll;
    return num;
}
public void keepRoll() {
    int dice1 = rollDice();
    int dice2 = rollDice();
    int dice3 = rollDice();
    while (!(dice1 == dice2 && dice2 == dice3)){
        dice1 = rollDice();
        dice2 = rollDice();
        dice3 = rollDice();
        count += 1;
    }
    test.setText(count);
}
}