這個問題在這里已有答案：

我試圖寫一個應用程序，如果在給定的URL中有一個文件，將字符串放在textview中，這是代碼和崩潰信息，可能是什么錯誤？

public class MainActivity extends AppCompatActivity {

String url = "https://images.pexels.com/photos/617278/pexels-photo-617278.jpeg?cs=srgb&dl=adorable-animal-blur-617278.jpg&fm=jpg";

TextView textView;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

textView.findViewById(R.id.textView);

try {

HttpURLConnection.setFollowRedirects(false);

HttpURLConnection connection = (HttpURLConnection) new URL(url).openConnection();

connection.setRequestMethod("HEAD");

connection.connect();

if(connection.getResponseCode() == HttpURLConnection.HTTP_OK){

textView.setText("File Exists!!");

}

} catch (IOException e) {

e.printStackTrace();

}

}

}

---------崩潰開始E / AndroidRuntime：FATAL EXCEPTION：main進程：com.example.android.archivoexiste，PID：6160 java.lang.RuntimeException：無法啟動活動ComponentInfo {com.example . android.archivoexiste / com.example.android.archivoexiste.MainActivity}：java.lang.NullPointerException：嘗試在android上的空對象引用上調用虛擬方法'android.view.View android.widget.TextView.findViewById(int)' Android.app.ActivityThread $中android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)的android.app.ActivityThread.-wrap11(未知來源：0)的.app.ActivityThread.performLaunchActivity(ActivityThread.java:2817) H.handleMessage(ActivityThread.java:1593)位于android.app.AooT.Thread.main的android.os.Handler.dispatchMessage(Handler.java:105)android.os.Looper.loop(Looper.java:164)(ActivityThread) .java：6541)在java.lang.reflect.Method.invoke(Native Method)的com.android.internal.os.Zygote $ MethodAndArgsCaller.run(Zygote.java:240)at at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)引起：java.lang.NullPointerException：嘗試調用虛擬方法'android.view.View android.widget.TextView.findViewById(int)'on位于android.app.Instrumentation.callActivityOnCreate(Instrumentation.java)的android.app.Activity.performCreate(Activity.java:6975)的com.example.android.archivoexiste.MainActivity.onCreate(MainActivity.java:23)中的空對象引用：1213)在android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2770)的android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)在android.app.ActivityThread.-wrap11(未知來源：0)在android .app.ActivityThread $ H.handleMessage(ActivityThread.java:1593)位于android.app的android.os.Handler.dispatchMessage(Handler.java:105)android.os.Looper.loop(Looper.java:164) . ActivityThread.main(ActivityThread.java:6541)at java.lang.reflect.Method.invoke(Native Method)at com.android.internal.os.Zygote $ MethodAndArgsCaller.run(Zygot) e.java:240)在com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)應用程序終止 .