Java

The following code is in MainActivity.java

package codebind.example.sqliteoperations;

import android.os.Bundle;
import android.view.View;
import android.widget.EditText;

import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {
    EditText Name, Pass , updateold, updatenew, delete;
    myDbAdapter helper;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Name= (EditText) findViewById(R.id.editName);
        Pass= (EditText) findViewById(R.id.editPass);
        updateold= (EditText) findViewById(R.id.editText3);
        updatenew= (EditText) findViewById(R.id.editText5);
        delete = (EditText) findViewById(R.id.editText6);

        helper = new myDbAdapter(this);
    }
    public void addUser(View view)
    {
        String t1 = Name.getText().toString();
        String t2 = Pass.getText().toString();
        if(t1.isEmpty() || t2.isEmpty())
        {
            Message.message(getApplicationContext(),"Enter Both Name and Password");
        }
        else
        {
            long id = helper.insertData(t1,t2);
            if(id<=0)
            {
                Message.message(getApplicationContext(),"Insertion Unsuccessful");
                Name.setText("");
                Pass.setText("");
            } else
            {
                Message.message(getApplicationContext(),"Insertion Successful");
                Name.setText("");
                Pass.setText("");
            }
        }
    }

    public void viewdata(View view)
    {
        String data = helper.getData();
        Message.message(this,data);
    }

    public void update( View view)
    {
        String u1 = updateold.getText().toString();
        String u2 = updatenew.getText().toString();
        if(u1.isEmpty() || u2.isEmpty())
        {
            Message.message(getApplicationContext(),"Enter Data");
        }
        else
        {
            int a= helper.updateName( u1, u2);
            if(a<=0)
            {
                Message.message(getApplicationContext(),"Unsuccessful");
                updateold.setText("");
                updatenew.setText("");
            } else {
                Message.message(getApplicationContext(),"Updated");
                updateold.setText("");
                updatenew.setText("");
            }
        }

    }
    public void delete( View view)
    {
        String uname = delete.getText().toString();
        if(uname.isEmpty())
        {
            Message.message(getApplicationContext(),"Enter Data");
        }
        else{
            int a= helper.delete(uname);
            if(a<=0)
            {
                Message.message(getApplicationContext(),"Unsuccessful");
                delete.setText("");
            }
            else
            {
                Message.message(this, "DELETED");
                delete.setText("");
            }
        }
    }
}

The following code is in myDbAdapter.java

package codebind.example.sqliteoperations;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;


public class myDbAdapter {
    myDbHelper myhelper;
    public myDbAdapter(Context context)
    {
        myhelper = new myDbHelper(context);
    }

    public long insertData(String name, String pass)
    {
        SQLiteDatabase dbb = myhelper.getWritableDatabase();
        ContentValues contentValues = new ContentValues();
        contentValues.put(myDbHelper.NAME, name);
        contentValues.put(myDbHelper.MyPASSWORD, pass);
        long id = dbb.insert(myDbHelper.TABLE_NAME, null , contentValues);
        return id;
    }

    public String getData()
    {
        SQLiteDatabase db = myhelper.getWritableDatabase();
        String[] columns = {myDbHelper.UID,myDbHelper.NAME,myDbHelper.MyPASSWORD};
        Cursor cursor =db.query(myDbHelper.TABLE_NAME,columns,null,null,null,null,null);
        StringBuffer buffer= new StringBuffer();
        while (cursor.moveToNext())
        {
            int cid =cursor.getInt(cursor.getColumnIndex(myDbHelper.UID));
            String name =cursor.getString(cursor.getColumnIndex(myDbHelper.NAME));
            String  password =cursor.getString(cursor.getColumnIndex(myDbHelper.MyPASSWORD));
            buffer.append(cid+ "   " + name + "   " + password +" \n");
        }
        return buffer.toString();
    }

    public  int delete(String uname)
    {
        SQLiteDatabase db = myhelper.getWritableDatabase();
        String[] whereArgs ={uname};

        int count =db.delete(myDbHelper.TABLE_NAME ,myDbHelper.NAME+" = ?",whereArgs);
        return  count;
    }

    public int updateName(String oldName , String newName)
    {
        SQLiteDatabase db = myhelper.getWritableDatabase();
        ContentValues contentValues = new ContentValues();
        contentValues.put(myDbHelper.NAME,newName);
        String[] whereArgs= {oldName};
        int count =db.update(myDbHelper.TABLE_NAME,contentValues, myDbHelper.NAME+" = ?",whereArgs );
        return count;
    }

    static class myDbHelper extends SQLiteOpenHelper
    {
        private static final String DATABASE_NAME = "myDatabase";    // Database Name
        private static final String TABLE_NAME = "myTable";   // Table Name
        private static final int DATABASE_Version = 1;    // Database Version
        private static final String UID="_id";     // Column I (Primary Key)
        private static final String NAME = "Name";    //Column II
        private static final String MyPASSWORD= "Password";    // Column III
        private static final String CREATE_TABLE = "CREATE TABLE "+TABLE_NAME+
                " ("+UID+" INTEGER PRIMARY KEY AUTOINCREMENT, "+NAME+" VARCHAR(255) ,"+ MyPASSWORD+" VARCHAR(225));";
        private static final String DROP_TABLE ="DROP TABLE IF EXISTS "+TABLE_NAME;
        private Context context;

        public myDbHelper(Context context) {
            super(context, DATABASE_NAME, null, DATABASE_Version);
            this.context=context;
        }

        public void onCreate(SQLiteDatabase db) {

            try {
                db.execSQL(CREATE_TABLE);
            } catch (Exception e) {
                Message.message(context,""+e);
            }
        }

        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
            try {
                Message.message(context,"OnUpgrade");
                db.execSQL(DROP_TABLE);
                onCreate(db);
            }catch (Exception e) {
                Message.message(context,""+e);
            }
        }
    }
}

The following code is in Message.java

package codebind.example.sqliteoperations;

import android.content.Context;
import android.widget.Toast;

public class Message {
    public static void message(Context context, String message) {
        Toast.makeText(context, message, Toast.LENGTH_LONG).show();
    }
}

The following code is in activity_main.xml

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

    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#4B1414">

    <TextView
        android:id="@+id/textView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentStart="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentTop="true"
        android:layout_marginTop="12dp"
        android:gravity="center"
        android:text="Student Name"
        android:textColor="#FFFFFF"
        android:textSize="18sp"
        android:textStyle="bold|italic" />

    <EditText
        android:id="@+id/editName"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@+id/textView"
        android:layout_alignParentEnd="true"
        android:layout_alignParentRight="true"
        android:ems="10"
        android:gravity="center_vertical|center"
        android:hint="Enter Name"
        android:inputType="textPersonName"
        android:textColor="#FFFFFF"
        android:textStyle="bold|italic" />

    <TextView
        android:id="@+id/textView2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@+id/editName"
        android:layout_alignParentEnd="true"
        android:layout_alignParentRight="true"
        android:layout_marginTop="13dp"
        android:gravity="center"
        android:hint="Enter Password"
        android:text="Parent Number"
        android:textColor="#FFFFFF"
        android:textSize="18sp"
        android:textStyle="bold|italic" />

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBaseline="@+id/button"
        android:layout_alignEnd="@+id/button4"
        android:layout_alignRight="@+id/button4"
        android:layout_alignBottom="@+id/button"
        android:onClick="viewdata"
        android:text="View Data"
        android:textSize="18sp"
        android:textStyle="bold|italic" />

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/editPass"
        android:layout_alignParentStart="true"
        android:layout_alignParentLeft="true"
        android:layout_marginStart="28dp"
        android:layout_marginLeft="28dp"
        android:layout_marginTop="23dp"
        android:onClick="addUser"
        android:text="Add User"
        android:textSize="18sp"
        android:textStyle="bold|italic" />

    <Button
        android:id="@+id/button3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/editText3"
        android:layout_alignStart="@+id/button4"
        android:layout_alignLeft="@+id/button4"
        android:layout_marginTop="13dp"
        android:onClick="update"
        android:text="Update"
        android:textStyle="normal|bold" />

    <EditText
        android:id="@+id/editText6"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignTop="@+id/button4"
        android:layout_alignParentStart="true"
        android:layout_alignParentLeft="true"
        android:layout_toStartOf="@+id/button2"
        android:layout_toLeftOf="@+id/button2"
        android:ems="10"
        android:freezesText="false"
        android:hint="Enter Name to Delete Data"
        android:inputType="textPersonName" />

    <Button
        android:id="@+id/button4"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentEnd="true"
        android:layout_alignParentRight="true"
        android:layout_alignParentBottom="true"
        android:layout_marginEnd="21dp"
        android:layout_marginRight="21dp"
        android:layout_marginBottom="41dp"
        android:onClick="delete"
        android:text="Delete"
        android:textStyle="normal|bold"
        tools:ignore="RelativeOverlap" />

    <EditText
        android:id="@+id/editText3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/button"
        android:layout_alignParentStart="true"
        android:layout_alignParentLeft="true"
        android:layout_marginStart="7dp"
        android:layout_marginLeft="7dp"
        android:layout_marginTop="47dp"
        android:ems="10"
        android:hint="Current Name"
        android:inputType="textPersonName"
        android:textColor="#FFFFFF"
        android:textSize="14sp"
        android:textStyle="bold|italic" />

    <EditText
        android:id="@+id/editPass"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@+id/textView2"
        android:layout_alignParentStart="true"
        android:layout_alignParentLeft="true"
        android:layout_marginTop="11dp"
        android:ems="10"
        android:gravity="center_vertical|center"
        android:hint="Enter Number"
        android:inputType="textPassword"
        android:textAllCaps="false"
        android:textSize="18sp"
        android:textStyle="normal|bold" />

    <EditText
        android:id="@+id/editText5"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignStart="@+id/editText3"
        android:layout_alignLeft="@+id/editText3"
        android:layout_alignTop="@+id/button3"
        android:layout_marginTop="32dp"
        android:ems="10"
        android:hint="New Name"
        android:inputType="textPersonName"
        android:textSize="14sp"
        android:textStyle="bold|italic" />

</RelativeLayout>

<pre>static long repeatedString1(String u, long n) {
		String[] a = u.split("");
		int s = a.length;
		int t = (int) n;
		int r = (t / s) + 1;
		String d = new String(new char[t]).replace("\0", u);
		String[] m = d.split("");
		long p = 0;
		if (s == 1) {
			p = t;
		} else {
			for (int i = 0; i < t; i++) {

				if (m[i].equals("a")) {
					p++;
				}
			}
		}
		return p;
	}

a java project on us reservation sytem

public class ReaderWriter{

   public static void main(String args[]){
	   
	   ReadWriteLock RW = new ReadWriteLock();
	   ExecutorService executorService = Executors.newCachedThreadPool();
  
	   executorService.execute(new Writer(RW));
		executorService.execute(new Writer(RW));
		executorService.execute(new Writer(RW));
		executorService.execute(new Writer(RW));
		
		executorService.execute(new Reader(RW));
		executorService.execute(new Reader(RW));
		executorService.execute(new Reader(RW));
		executorService.execute(new Reader(RW));

  }
}
//Writer class
class Writer implements Runnable
{
   private ReadWriteLock rwlock;
   private int writerNum;

    public Writer(int w, ReadWriteLock rw) {
      writerNum = w;
      rwlock = rw;
   }

    public void run() {
      while (true){
         SleepUtilities.nap();
      
         System.out.println("writer " + writerNum + " wants to write.");
         rwlock.WriteLock(writerNum);

         SleepUtilities.nap();
      
         rwlock.WriteUnLock(writerNum);
      }
   }
}

//Reader class
class Reader implements Runnable
{

   private ReadWriteLock rwlock;
   private int readerNum;

    public Reader(int readerNum, ReadWriteLock database) {
      this.readerNum = readerNum;
      this.rwlock = database;
   }

    public void run() {
      while (true) {
         SleepUtilities.nap();
         System.out.println("reader " + readerNum + " wants to read.");
         rwlock.ReadLock(readerNum);
      
      // you have access to read from the database
      // let's read for awhile .....
         SleepUtilities.nap();
      
         rwlock.ReadUnLock(readerNum);
      }
   };
}

//Lock class
class ReadWriteLock {
    private int readerCount;
    private Semaphore mutex; 
    private Semaphore rwlock;     
 
     public ReadWriteLock() {
       readerCount = 0;
       mutex = new Semaphore(1);
       rwlock = new Semaphore(1);
    }
 
     public void ReadLock(int readerNum) {
       try{
          mutex.acquire();
       }
           catch (InterruptedException e) {
        	   
           }
       ++readerCount;
    

       if (readerCount == 1){
          try{
        	  rwlock.acquire();
          }
              catch (InterruptedException e) {
            	  
              }
       }
    
       System.out.println("Reader " + readerNum + " is reading. Reader count = " + readerCount);
       mutex.release();
    }
 
     public void ReadUnLock(int readerNum) {
       try{
          mutex.acquire();
       }
           catch (InterruptedException e) {}
    
       --readerCount;

       if (readerCount == 0){
    	   rwlock.release();
       }
    
       System.out.println("Reader " + readerNum + " is done reading. Reader count = " + readerCount);

       mutex.release();
    }
 
     public void WriteLock(int writerNum) {
       try{
    	   rwlock.acquire();
       }
           catch (InterruptedException e) {}
       System.out.println("Writer " + writerNum + " is writing.");
    }
 
     public void WriteUnLock(int writerNum) {
       System.out.println("Writer " + writerNum + " is done writing.");
       rwlock.release();
    }
 }
class SleepUtilities
{
    public static void nap() {
      nap(NAP_TIME);
   }

    public static void nap(int duration) {
      int sleeptime = (int) (NAP_TIME * Math.random() );
      try { RW.sleep(sleeptime*1000); }
          catch (InterruptedException e) {}
   }

   private static final int NAP_TIME = 5;
}