==============================================================
===============MAIN ACTIVITY CLASS============================
==============================================================
package com.example.app0811.login;

import android.app.Activity;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.EditText;
import android.widget.Toast;

public class MainActivity extends Activity {

    EditText txtUser;
    EditText txtPass;
    String userNameLogged;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        txtUser = (EditText)findViewById(R.id.username);
        txtPass = (EditText)findViewById(R.id.pass);
        if (userLogged())
        {
            Intent iLogged = new Intent(this,Hello.class);
            iLogged.putExtra("userName",userNameLogged);
            this.startActivity(iLogged);
        }
    }
    private boolean userLogged()
    {
        SharedPreferences myPref = getApplicationContext().getSharedPreferences("myPref", MODE_PRIVATE);
        userNameLogged = myPref.getString("logged", "error");
        if (userNameLogged.equals("error"))
        {
            //we not logged in
            return  false;
        }
        else
        {
            //we are logged in
            return true;
        }
    }

    public void onClick (View v)
    {
        if (chkUser())
        {
            Intent helloIntent = new Intent(this , Hello.class);
            this.startActivity(helloIntent);
        }
        else
        {
            Toast.makeText(this,"Wrong user name or password!!",Toast.LENGTH_LONG).show();
        }

    }

    private boolean chkUser()
    {
        SharedPreferences myPref = getApplicationContext().getSharedPreferences("myPref",MODE_PRIVATE);
        String userName = myPref.getString("userName", "error");
        String userPass = myPref.getString("password","error");
        if (userName.equals(txtUser.getText().toString()) && userPass.equals(txtPass.getText().toString()))
        {
            return true;
        }
        else
        {
            return false;
        }
    }

    public void btnReg (View v)
    {
        Intent intentReg = new Intent(this, Register.class);
        this.startActivity(intentReg);
    }

}


==============================================================
===============HELLO CLASS============================
==============================================================

package com.example.app0811.login;

import android.app.Activity;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;

/**
 * Created by app0811 on 06/03/2016.
 */
public class Hello extends Activity
{
    SharedPreferences myPrefs; //calling SharedPrefrences Class
    SharedPreferences.Editor editor;//calling the editor for SharedPrefrences

    TextView myTxt;
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.hello);
        setPoints();
        myTxt.setText("Hello "+ getUser());
    }

    private void setPoints()
    {
        myTxt = (TextView)findViewById(R.id.hellotxt);
        myPrefs = getApplicationContext().getSharedPreferences("myPref",MODE_PRIVATE);
        editor = myPrefs.edit();
    }

    private String getUser()
    {
        String user = myPrefs.getString("userName","error");
        return user;
    }

    public void btnExit(View v)
    {
        editor.remove("logged");
        editor.commit();

        Intent exit = new Intent(this,MainActivity.class);
        this.startActivity(exit);
    }


}

==============================================================
===============REGISTER CLASS=================================
==============================================================

package com.example.app0811.login;

import android.app.Activity;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.Toast;

/**
 * Created by app0811 on 06/03/2016.
 */
public class Register extends Activity

    {
        private SharedPreferences myPrefs;//calling SharedPrefrences Class
        private  SharedPreferences.Editor editor;//calling the editor for SharedPrefrences

        private EditText crUser;//create user
        private EditText crPass;//password
        private EditText confPass;//confirm password


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

            setPoint();
        }

        private void setPoint()
        {
            crUser = (EditText)findViewById(R.id.crUser);
            crPass = (EditText)findViewById(R.id.crPass);
            confPass = (EditText)findViewById(R.id.confPass);
            //creating the sharedprefrences xml file
            myPrefs = getApplicationContext().getSharedPreferences("myPref",MODE_PRIVATE);
            editor = myPrefs.edit();
        }

        public void creatUser(View v)
        {
          String userName = crUser.getText().toString();
          String userPass = crPass.getText().toString();
          String confirmPass = confPass.getText().toString();
          String chkUser = "";

            if (userName.trim().length()<=0 || userPass.trim().length()<=0 || confirmPass.trim().length()<=0)
            {
                Toast.makeText(this,"Please fill all the fields above",Toast.LENGTH_LONG).show();
            }
            else if (!userPass.equals(confirmPass))
            {
                Toast.makeText(this, "The password not confirm" ,Toast.LENGTH_LONG).show();
            }
            else if(userName.equals(myPrefs.getString("username",chkUser)))
            {
                Toast.makeText(this, "This username is taken" , Toast.LENGTH_LONG).show();
            }
            else
            {
                editor.putString("userName" ,userName );
                editor.putString("password", userPass);
                editor.commit();
                Toast.makeText(this , "The username creating" ,Toast.LENGTH_LONG).show();
                Intent intentMain = new Intent(this,MainActivity.class);
                this.startActivity(intentMain);
            }

        }

        public void btncancel (View v)
        {
            Intent mainIntent = new Intent(this , MainActivity.class);
            this.startActivity(mainIntent);
        }
    }

==================activity main xml=================

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical"
        xmlns:android="http://schemas.android.com/apk/res/android" >

        <EditText
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:hint="Username"
            android:id="@+id/username"/>
        <EditText
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:hint="Password"
            android:id="@+id/pass"/>

        <Button
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="Login"
            android:id="@+id/btnLogin"
            android:onClick="onClick"/>

        <Button
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="Register"
            android:id="@+id/btnRegister"
            android:onClick="btnReg"
            />


    </LinearLayout>



    =======================hello xml===================

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

        <TextView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="Hello"
            android:textSize="54sp"
            android:id="@+id/hellotxt"/>
        <Button
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="Logout"
            android:id="@+id/btnlogout"
            android:onClick="btnExit"/>
    </LinearLayout>

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

        <EditText
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:hint="Enter Username"
            android:id="@+id/crUser"
            />
        <EditText
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:hint="Password"
            android:id="@+id/crPass"/>
        <EditText
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:hint="Password2"
            android:id="@+id/confPass"/>
        <Button
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="Register"
            android:onClick="creatUser"
            />
        <Button
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="Cancel"
            android:onClick="btncancel"/>

    </LinearLayout>