D/AndroidRuntime： 关闭虚拟机 E/Android运行时：致命异常：main 进程： com.example.hello， PID： 26685 java.lang.RuntimeException： 无法启动活动 ComponentInfo{com.example.hello/com.example.hello.MainActivity}： java.lang.NullPointerException： 尝试在空对象引用上调用虚拟方法 'void androidx.recyclerview.widget.RecyclerView.setLayoutManager(androidx.recyclerview.widget.RecyclerView$LayoutManager(' at android.app.ActivityThread.performLaunchActivity(ActivityThread.java：2913( at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java：3048( at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java：78( at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java：108( at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java：68( at android.app.ActivityThread$H.handleMessage(ActivityThread.java：1808( at android.os.Handler.dispatchMessage(Handler.java：106( at android.os.Looper.loop(Looper.java：193( at android.app.ActivityThread.main(ActivityThread.java：6669( at java.lang.reflect.Method.invoke(Native Method( at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java：493( at com.android.internal.os.ZygoteInit.main(ZygoteInit.java：858( 由：java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法'void androidx.recyclerview.widget.RecyclerView.setLayoutManager(androidx.recyclerview.widget.RecyclerView$LayoutManager(' at com.example.hello.MainActivity.loadRecyclerViewData(MainActivity.java：93( at com.example.hello.MainActivity.onCreate(MainActivity.java：42( at android.app.Activity.performCreate(Activity.java：7136( at android.app.Activity.performCreate(Activity.java：7127( at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java：1271( at android.app.ActivityThread.performLaunchActivity(ActivityThread.java：2893( at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java：3048( at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java：78( at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java：108( at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java：68( at android.app.ActivityThread$H.handleMessage(ActivityThread.java：1808( at android.os.Handler.dispatchMessage(Handler.java：106( at android.os.Looper.loop(Looper.java：193( at android.app.ActivityThread.main(ActivityThread.java：6669( at java.lang.reflect.Method.invoke(Native Method( at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java：493( at com.android.internal.os.ZygoteInit.main(ZygoteInit.java：858( E/Volley： [1025] NetworkDispatcher.processRequest： Unhandle exception java.lang.ClassCastException： sun.net.www.protocol.file.FileURLConnection 不能强制转换为 java.net.HttpURLConnection java.lang.ClassCastException： sun.net.www.protocol.file.FileURLConnection 不能强制转换为 java.net.HttpURLConnection at com.android.volley.toolbox.HurlStack.createConnection(HurlStack.java：189( at com.android.volley.toolbox.HurlStack.openConnection(HurlStack.java：207( at com.android.volley.toolbox.HurlStack.executeRequest(HurlStack.java：88( at com.android.volley.toolbox.BasicNetwork.performRequest(BasicNetwork.java：123( at com.android.volley.NetworkDispatcher.processRequest(NetworkDispatcher.java：131( at com.android.volley.NetworkDispatcher.processRequest(NetworkDispatcher.java：111( at com.android.volley.NetworkDispatcher.run(NetworkDispatcher.java：90( I/进程：发送信号。PID： 26685 SIG： 9
设置布局管理器时，RecyclerView 实例为空：
ava.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.recyclerview.widget.RecyclerView.setLayoutManager(androidx.recyclerview.widget.RecyclerView$LayoutManager)' on a null object reference at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2913)