My new app crashing in phone but there is no error in codes

Question

I am new to android developing. My new app is crashing in my phone (i am using my phone instead if a virtual machine) but the codes are right please help

05-16 17:36:52.717 28823-28823/ebin.namez I/art: Late-enabling -Xcheck:jni
05-16 17:36:52.728 27804-27886/? I/PBSessionCacheImpl: Deleted sessionId[122284780131059156] from persistence.
05-16 17:36:52.778 28823-28823/ebin.namez W/System: ClassLoader referenced unknown path: /data/app/ebin.namez-2/lib/arm64
05-16 17:36:52.800 28823-28823/ebin.namez D/AndroidRuntime: Shutting down VM
05-16 17:36:52.801 28823-28823/ebin.namez E/AndroidRuntime: FATAL EXCEPTION: main
 Process: ebin.namez, PID: 28823
    java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{ebin.namez/ebin.namez.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2583)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2742)
        at android.app.ActivityThread.-wrap12(ActivityThread.java)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1489)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:154)
        at android.app.ActivityThread.main(ActivityThread.java:6178)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:891)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:781)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
        at android.support.v7.app.AppCompatDelegateImplBase.<init>(AppCompatDelegateImplBase.java:116)
        at android.support.v7.app.AppCompatDelegateImplV9.<init>(AppCompatDelegateImplV9.java:147)
        at android.support.v7.app.AppCompatDelegateImplV11.<init>(AppCompatDelegateImplV11.java:27)
        at android.support.v7.app.AppCompatDelegateImplV14.<init>(AppCompatDelegateImplV14.java:53)
        at android.support.v7.app.AppCompatDelegateImplV23.<init>(AppCompatDelegateImplV23.java:29)
        at android.support.v7.app.AppCompatDelegateImplN.<init>(AppCompatDelegateImplN.java:29)
        at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:201)
        at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:185)
        at android.support.v7.app.AppCompatActivity.getDelegate(AppCompatActivity.java:525)
        at android.support.v7.app.AppCompatActivity.findViewById(AppCompatActivity.java:193)
        at ebin.namez.MainActivity.<init>(MainActivity.java:36)
        at java.lang.Class.newInstance(Native Method)
        at android.app.Instrumentation.newActivity(Instrumentation.java:1079)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2573)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2742) 
        at android.app.ActivityThread.-wrap12(ActivityThread.java) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1489) 
        at android.os.Handler.dispatchMessage(Handler.java:102) 
        at android.os.Looper.loop(Looper.java:154) 
        at android.app.ActivityThread.main(ActivityThread.java:6178) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:891) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:781) `

Here is the code to MainActivity

package ebin.namez;

import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;


public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

       FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "nothing", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();

            }
        });
    }
    TextView op;
    {
        op=(TextView)findViewById(R.id.op);
    }
    Button button;

    {
        button = (Button) findViewById(R.id.button);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                op.setText("hey");
            }
        });
    }



    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}

this is a simple program that displays "hey" when the button is pressed

Possible duplicate of [What is a NullPointerException, and how do I fix it?](http://stackoverflow.com/questions/218384/what-is-a-nullpointerexception-and-how-do-i-fix-it) — Phantômaxx, May 16 '17 at 12:21
`... but the codes are right ...` No, **it's not**. Because it causes an NPE. — Phantômaxx, May 16 '17 at 12:22
@Rotwang it is not a duplicate of the canonical NPE question, because the NPE is not directly in the OP's code, and the methods described in that other question are not sufficient to fix the issue at hand. — njzk2, May 16 '17 at 15:04
It is actually an **NPE**. And it is solved as you would solve an NPE. — Phantômaxx, May 16 '17 at 19:12

makadev · Accepted Answer · 2017-05-16T14:57:05.987

The error says you got a NullPointerExeception at ebin.namez.MainActivity.<init>(MainActivity.java:36). That is the line op=(TextView)findViewById(R.id.op) which is in an initializer block - if you posted that code 1:1.

This block is executed on instance creation before the Activity is setup correctly. Activity is a Component and its Lifecycle starts with onCreate, so accessing Component properties and methods like findViewById on instance Creation is a pretty bad idea.

public class MainActivity extends AppCompatActivity {

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

  // Member op
  TextView op;

  // initializer block: executed on instance creation
  {
      op=(TextView)findViewById(R.id.op); // Line 36
  }
...
}

You probably wanted that code for op and button in the onCreate method like so:

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

    // local variable op, declared final for use in anonymous class method
    final TextView op = (TextView)findViewById(R.id.op);

    // local variable button
    Button button;
    button = (Button) findViewById(R.id.button);
    button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            op.setText("hey");
        }
    });
}

My new app crashing in phone but there is no error in codes

1 Answers1