Getting error in changing co-ordinates of imageview in android studio

I am a beginner to android. I want to slide a slidebar in a horizontal linear layout but when I run the code, the application ends giving error FallingBall keeps stopping

My 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">


<LinearLayout
    android:id="@+id/linearLayout2"
    android:layout_width="0dp"
    android:layout_height="0dp"
    android:orientation="vertical"
    android:weightSum="100"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent">

    <LinearLayout
        android:id="@+id/linearLayout"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_weight="72"
        android:orientation="horizontal" >

        <TextView
            android:id="@+id/textView2"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:text="Hello" />
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="8"
        android:orientation="horizontal">

        <ImageView
            android:id="@+id/slideBar"
            android:layout_width="100dp"
            android:layout_height="match_parent"
            app:srcCompat="@android:drawable/bottom_bar" />
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="20"
        android:orientation="horizontal">

        <androidx.constraintlayout.widget.ConstraintLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent">

            <ImageButton
                android:id="@+id/leftBut"
                android:layout_width="wrap_content"
                android:layout_height="match_parent"
                android:background="@android:color/white"
                app:layout_constraintBottom_toBottomOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toTopOf="parent"
                app:srcCompat="@drawable/left_but"
                android:onClick="hitLeft"/>

            <ImageButton
                android:id="@+id/rightBut"
                android:layout_width="wrap_content"
                android:layout_height="match_parent"
                android:background="@android:color/white"
                app:layout_constraintBottom_toBottomOf="parent"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintTop_toTopOf="parent"
                app:srcCompat="@drawable/right_but"
                android:onClick="hitRight"/>
        </androidx.constraintlayout.widget.ConstraintLayout>

    </LinearLayout>
</LinearLayout>

</androidx.constraintlayout.widget.ConstraintLayout>

My java file is like this:

    package com.example.fallingball;

import androidx.appcompat.app.AppCompatActivity;

import android.content.pm.ActivityInfo;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.ImageButton;
import android.widget.ImageView;

public class MainActivity extends AppCompatActivity {

ImageView s = findViewById(R.id.slideBar);
float x = s.getX();
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE);
}


void hitLeft(View view){
    x--;
    s.setX(30);
}

void hitRight(View view){
    x++;
    s.setX(40);
}
}

Note: leftBut and rightBut are two Image button and I have copied the images to the drawable folder so if you are trying this code on your system, make sure you adjust this else it will show you Image not found or so...