Java 如何在Android Studio的WebView小部件中加载URL？

每当我尝试在我的activity_main.xml布局中的WebView小部件中加载URL时，就会出现此错误：

Attempt to invoke virtual method 'void android.webkit.WebView.loadUrl(java.lang.String)' on a null object reference

这是我用来在WebView小部件中加载URL的代码：

package com.example.webviewapp;

import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.webkit.WebView;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity
{

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

        final EditText url_inputedttext = (EditText)findViewById(R.id.url_inputedttext);
        final Button url_navigatebtn = (Button) findViewById(R.id.url_navigatebtn);
        final WebView url_displaywebview = (WebView)findViewById(R.id.url_displaywebview);

        url_navigatebtn.setOnClickListener(new Button.OnClickListener()
        {
            @Override
            public void onClick(View v) {
                url_displaywebview.loadUrl(url_inputedttext.getText().toString());
            }
        });



    }

}

当然，我已经在activity_main.xml文件中附加了WebView小部件，请参见下面的代码：

<?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">


    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:layout_editor_absoluteX="1dp"
        tools:layout_editor_absoluteY="1dp">

        <TextView
            android:id="@+id/url_labeltxtview"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="100dp"
            android:layout_centerHorizontal="true"
            android:text="@string/website_url"
            android:textAlignment="center"
            android:textSize="25dp"
            android:textStyle="bold" />
        <EditText
            android:id="@+id/url_inputedttext"
            android:layout_width="320dp"
            android:layout_height="wrap_content"
            android:layout_below="@+id/url_labeltxtview"
            android:layout_marginTop="50dp"
            android:layout_centerHorizontal="true"
            android:tooltipText="Url goes here!"
            android:hint="Enter Website URL..."
            android:text="https://www.google.com/"
            android:textColorHint="@color/colorPrimaryDark"/>
        <Button
            android:id="@+id/url_navigatebtn"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="30dp"
            android:layout_centerHorizontal="true"
            android:layout_below="@+id/url_inputedttext"
            android:text="Navigate"
            android:textAllCaps="false"
            android:textSize="18dp"/>
        <WebView
            android:id="@+id/url_displaywebview"
            android:layout_width="match_parent"
            android:layout_height="400dp"
            android:layout_marginTop="10dp"
            android:layout_below="@+id/url_navigatebtn"/>

    </RelativeLayout>
</androidx.constraintlayout.widget.ConstraintLayout>

我当时真的很困惑，也许我遗漏了什么，有人能帮我吗