如何添加在WebView无法返回时隐藏的后退按钮

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <WebView
        android:id="@+id/webView"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

    <Button
        android:id="@+id/backButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="后退"
        android:visibility="gone" />

</RelativeLayout>

WebView webView = findViewById(R.id.webView);
Button backButton = findViewById(R.id.backButton);

webView.setWebChromeClient(new WebChromeClient());
webView.setWebViewClient(new WebViewClient());

webView.setWebViewClient(new WebViewClient() {
    @Override
    public boolean shouldOverrideUrlLoading(WebView view, String url) {
        if (view.canGoBack()) {
            backButton.setVisibility(View.VISIBLE);
        } else {
            backButton.setVisibility(View.GONE);
        }
        return false;
    }
});

backButton.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        webView.goBack();
    }
});