example of what we done in the class

MainActivity.java
=======================
package com.example.zeevm.mysharedpref;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    EditText txtUserName;
    EditText txtUserPass;
    TextView lblMsg;

    private int totalTry=5;
    Button btnLogin;
    Button btnRegister;

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

    private void setPointer()
    {
        txtUserName=(EditText)findViewById(R.id.txtUserName);
        txtUserPass=(EditText)findViewById(R.id.txtUserPassword);
        lblMsg=(TextView)findViewById(R.id.lblMsg);
        btnLogin=(Button)findViewById(R.id.btnLogin);
        btnRegister=(Button)findViewById(R.id.btnRegister);

        //listerners
        btnLogin.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
               login();
            }
        });

        btnRegister.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                register();
            }
        });
    }

    private void login()
    {
        String getUser=txtUserName.getText().toString();
        String getPass=txtUserPass.getText().toString();

        if (totalTry==0) {
            Toast.makeText(MainActivity.this, "You are an idiot!!", Toast.LENGTH_SHORT).show();
            return;
        }
        /*
        if (getUser.equals(MY_USER) && getPass.equals(MY_PASS))
        {
            lblMsg.setText("User loged...");
        }
        else
        {
            totalTry--;
            Toast.makeText(MainActivity.this, "you have "+totalTry+" times", Toast.LENGTH_LONG).show();

        }
        */
    }

    private void register()
    {
        startActivity(new Intent(this,Register.class));
    }

}


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

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="150dp"
        android:orientation="vertical">

        <TextView
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:gravity="center"
            android:text="LOGO"
            android:textSize="100sp">

        </TextView>
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="100dp"
        android:orientation="vertical">

        <EditText
            android:id="@+id/txtUserName"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:hint="Enter your name...."
            android:inputType="text"
            android:textSize="22sp" />

        <EditText
            android:id="@+id/txtUserPassword"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:hint="Enter Password..."
            android:inputType="textPassword"
            android:textSize="22sp" />
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="150dp"
        android:orientation="vertical">

        <Button
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="Login"
            android:background="#00BFFF"
            android:textColor="#ffffff"
            android:textSize="32sp"
            android:id="@+id/btnLogin"
            android:layout_marginBottom="20dp"/>

        <Button
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="Register"
            android:background="#00BFFF"
            android:textColor="#ffffff"
            android:textSize="32sp"
            android:id="@+id/btnRegister"/>
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">
        <TextView
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:textSize="32sp"
            android:text="MY LOGIN SYSTEM V1"
            android:gravity="center"
            android:id="@+id/lblMsg"/>
    </LinearLayout>
</LinearLayout>


utlShared.java
====================
package com.example.zeevm.mysharedpref;

import android.content.Context;
import android.content.SharedPreferences;
import android.util.Log;

/**
 * Created by zeevm on 8/25/2016.
 */
public class utlShared {
    //context to use later
    Context context;
    //declatrtion of shared preferences object
    private SharedPreferences userPref;
    //declaration of shared preferences editor
    private SharedPreferences.Editor editor;

    public utlShared() {}

    public utlShared(Context context)
    {
        //get context to use it
        this.context=context;
        //declaretion of shared preferences with file name and file mode (private,public)
        userPref=context.getSharedPreferences("users",Context.MODE_PRIVATE);
        //declaration of editor
        editor=userPref.edit();
    }

    //get user and password
    public void addUser(String userName, String password)
    {
        //stores in the phone device under data\data\package name
        //put in shared preferences user name and password
        editor.putString(userName,password);
        //commit (save/apply) the changes.
        editor.commit();
    }

    public boolean checkUser(String userName)
    {
        //get name by key->userName
        String checkString = userPref.getString(userName,"na");

        //print to logcat a custom message.....
        Log.e("checkUser", "checkUser: "+checkString );
        //check if userName equals to responded data, if it's na, we don't havce the user...
        return !checkString.equals("na");
    }
}


Register.java
====================
package com.example.zeevm.mysharedpref;

import android.content.Context;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class Register extends AppCompatActivity {

    Button btnCancel;
    Button btnRegister;
    Context context;
    EditText txtUser,txtPass;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_register);
        this.context=this;
        setPointer();
    }

    private void setPointer()
    {
        txtUser=(EditText)findViewById(R.id.txtUserName);
        txtPass=(EditText)findViewById(R.id.txtPassword);
        btnCancel=(Button)findViewById(R.id.btnCancel);
        btnCancel.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                finish();
            }
        });

        btnRegister=(Button)findViewById(R.id.btnRegisterUser);
        btnRegister.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                //calling the utl shared class
                utlShared myShared = new utlShared(context);
                //check if user exists
                if (myShared.checkUser(txtUser.getText().toString()))
                {
                    Toast.makeText(context, "User Exists....", Toast.LENGTH_SHORT).show();
                    return;
                }
                //running the method of add user
                myShared.addUser(txtUser.getText().toString(),txtPass.getText().toString());
                finish();
            }
        });
    }

}


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

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="20dp"
        android:gravity="center"
        android:text="USER REGISTERTION"
        android:textSize="32sp" />

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <EditText
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:hint="Enter User Name...."
            android:id="@+id/txtUserName"/>
        <EditText
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:hint="Enter password...."
            android:id="@+id/txtPassword"
            android:layout_below="@id/txtUserName"/>

        <EditText
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:hint="Enter password again..."
            android:id="@+id/txtPassword2"
            android:layout_below="@id/txtPassword"/>
        <Button
            android:layout_width="150dp"
            android:layout_height="wrap_content"
            android:id="@+id/btnRegisterUser"
            android:layout_below="@id/txtPassword2"
            android:text="Register"/>
        <Button
            android:layout_width="150dp"
            android:layout_height="wrap_content"
            android:text="Cancel"
            android:id="@+id/btnCancel"
           android:layout_toEndOf="@id/btnRegisterUser"
            android:layout_below="@id/txtPassword2"/>
    </RelativeLayout>

</LinearLayout>