It seems to be thread preemption because sometimes it works and sometimes it doesn't

Seems to be a thread problem but I don't know how to solve it by taking out the url of all the images from the first url and adding them to the list again But occasionally this program will work and occasionally it won't, and it will have the following error.

 private Handler handler=new Handler(){
        @Override
        public void handleMessage(@NonNull Message msg) {
            super.handleMessage(msg);
            byte[] result= (byte[]) msg.obj;
            Bitmap bitmap= BitmapFactory.decodeByteArray(result,0,result.length);
            list.add(bitmap);
            recyclerView=findViewById(R.id.recyclerview);
            linearLayoutManager=new LinearLayoutManager(MainActivity4.this);
            adaptern1=new adaptern1(MainActivity4.this,list);
            recyclerView.setLayoutManager(linearLayoutManager);
            recyclerView.setAdapter(adaptern1);
        }
    };
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main4);
        downAsynFile();
    }
    private void downAsynFile() {new Thread(new Runnable() {
        @Override
        public void run() {
            try {
                OkHttpClient client = new OkHttpClient();
                Request request = new Request.Builder()
                        .url("http://mrobot.pcauto.com.cn/v2/cms/channels/3?pageNo=1&pageSize=20&v=4.0.0")
                        .build();
                Response response = client.newCall(request).execute();
                String responseData = response.body().string();
              parseJSONWithGSON(responseData);
            } catch (Exception e) {
                e.printStackTrace(); }}
    }).start(); }
    private void parseJSONWithGSON(String jsonData) {
        Gson gson = new Gson();
        Data data=gson.fromJson(jsonData,Data.class);
        showResponse(data); }
    public void showResponse(Data data){runOnUiThread(new Runnable() {
        @Override
        public void run() {
            List<Data.DataBean> dataBeans=data.getData();
            for (Data.DataBean dataBean : dataBeans) {
                String a=dataBean.getImage();
              sendrequest(a);
                } }});}
    public void sendrequest(String a) {new Thread(new Runnable() {
        @Override
        public void run() {
            OkHttpClient okHttpClient=new OkHttpClient();
            Request request=new Request.Builder()
                    .url(a)
                    .build();
            okHttpClient.newCall(request).enqueue(new Callback() {
                @Override
                public void onFailure(@NotNull Call call, @NotNull IOException e) {
                }
                @Override
                public void onResponse(@NotNull Call call, @NotNull Response response) throws IOException {
                    Message message=handler.obtainMessage();
                    message.obj=response.body().bytes();
                    handler.sendMessage(message);
                }
            }); }}).start();}}

The following is an error message

2023-02-20 18:31:31.612 5635-5665/com.example.myapplication E/AndroidRuntime: FATAL EXCEPTION: Thread-3
    Process: com.example.myapplication, PID: 5635
    java.lang.IllegalArgumentException: Expected URL scheme 'http' or 'https' but no colon was found
        at okhttp3.HttpUrl$Builder.parse$okhttp(HttpUrl.kt:1260)
        at okhttp3.HttpUrl$Companion.get(HttpUrl.kt:1633)
        at okhttp3.Request$Builder.url(Request.kt:184)
        at com.example.myapplication.MainActivity4$4.run(MainActivity4.java:89)
        at java.lang.Thread.run(Thread.java:923)
2023-02-20 18:31:31.612 5635-5666/com.example.myapplication E/AndroidRuntime: FATAL EXCEPTION: Thread-4
    Process: com.example.myapplication, PID: 5635
    java.lang.IllegalArgumentException: Expected URL scheme 'http' or 'https' but no colon was found
        at okhttp3.HttpUrl$Builder.parse$okhttp(HttpUrl.kt:1260)
        at okhttp3.HttpUrl$Companion.get(HttpUrl.kt:1633)
        at okhttp3.Request$Builder.url(Request.kt:184)
        at com.example.myapplication.MainActivity4$4.run(MainActivity4.java:89)
        at java.lang.Thread.run(Thread.java:923)