Unfortunately “app_name” has stopped

Question

Hello I am new in android developping, I made a small test but it's giving me that error : 'Unfortunately android test has stopped'

I sought some similar topics here, but no one resolved my problem, here is my code :

main activity :

public class MainActivity extends ActionBarActivity {

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

        if (savedInstanceState == null) {
            getSupportFragmentManager().beginTransaction()
                    .add(R.id.container, new PlaceholderFragment()).commit();
        }

        final EditText username = (EditText) findViewById(R.id.username);
        final EditText password = (EditText) findViewById(R.id.password);
        Button button = (Button) findViewById(R.id.button1);

        button.setOnClickListener(new View.OnClickListener() {

            public void onClick(View v) {
                if(checkLogin(username.getText().toString(),password.getText().toString())){
                    Intent i = new Intent(MainActivity.this, HelloActivity.class);
                    startActivity(i);
                }
                else{
                    username.setText("");
                    password.setText("");
                }

            }
        });
    }

    private boolean checkLogin(String u,String p){
        if (u == "hello" && p == "world")
            return true;
        else return false;

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {

        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.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();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    /**
     * A placeholder fragment containing a simple view.
     */
    public static class PlaceholderFragment extends Fragment {

        public PlaceholderFragment() {
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_main, container,
                    false);
            return rootView;
        }
    }

}

the main layout :

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/login"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.androidtest.MainActivity$PlaceholderFragment" >

    <EditText
        android:id="@+id/username"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentTop="true"
        android:layout_marginLeft="16dp"
        android:ems="10"
        android:hint="username" >

        <requestFocus />
    </EditText>

    <EditText
        android:id="@+id/password"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignRight="@+id/username"
        android:layout_below="@+id/username"
        android:ems="10"
        android:hint="password"
        android:inputType="textPassword" />

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/username"
        android:layout_below="@+id/password"
        android:text="Button" />

</RelativeLayout>

the second acivity

package com.androidtest;

import android.app.Activity;
import android.os.Bundle;

public class HelloActivity extends Activity {

    public void onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);
        this.setContentView(R.layout.hello_layout);

    }

}

its layout

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="193dp"
        android:text="Afin akhay lpchiiwr"
        android:textAppearance="?android:attr/textAppearanceLarge" />

</RelativeLayout>

and finally the Manifest file :

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.androidtest"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="19" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.androidtest.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity android:name="com.androidtest.HelloActivity"></activity>
    </application>

</manifest>

Thanx

Answer 1

The first xml block you've posted looks like it's from the fragment_main.xml file. If so, then your problem is that findViewById() is looking for Views in the Activity that have been inflated into the Fragment. If you don't need the Fragment, then move that xml to activity_main.xml and remove the code for the Fragment. Otherwise, move the View initializations and methods to your Fragment.

And, as Kedarnath points out, you should use the String.equals() method to compare Strings.

Answer 2

First of all let me tell you that you are comparing String in wrong way,

private boolean checkLogin(String u,String p)
{
        if (u == "hello" && p == "world")     // Wrong way
            return true;
        else return false;
}

You need to compare string in following way,

private boolean checkLogin(String u,String p)
{
        if (u.equals("hello") && p.equals("world") )     // Right way
            return true;
        else return false;
}