Logics:
1)Tip Calculator
super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        binding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)
 
        binding.button.setOnClickListener() {
            calculateTip()
        }
    }
    fun calculateTip()
    {
        val cost =(binding.cost.text.toString()).toDouble()
        val selected =binding.RG.checkedRadioButtonId
        val tipPercent=when(selected)
        {
            R.id.radioButton ->15
            R.id.radioButton2 ->18
            else -> 20
        }
        var tip=tipPercent*cost
        if(binding.switch2.isChecked)
        {
            tip= ceil(tip)
        }
        binding.textView7.text=tip.toString()
    }
}
2)Toast message
val button:Button=findViewById(R.id.button)
        button.setOnClickListener{
            Toast.makeText(this,"Clicked",Toast.LENGTH_LONG).show()
        }
3)dice roller
val button: Button=findViewById(R.id.button)
        button.setOnClickListener{
            rollDice()
        }
    }
    private fun rollDice(){
        val dice=Dice(6)
        val diceRoll=dice.roll()
        val img :ImageView=findViewById(R.id.imageView)
        val drawableResource = when(diceRoll){
            1->R.drawable.dice1
            2->R.drawable.dice2
            3->R.drawable.dice3
            4->R.drawable.dice4
            5->R.drawable.dice5
            else->R.drawable.dice5
        }
        img.setImageResource(drawableResource)
    }
}
class Dice(private val numsides:Int){
    fun roll():Int{
        return (1..numsides).random()
    }
}
4)explicit intent
//Explicit Intent
        var t: TextView = findViewById(R.id.textView)
        var f: FloatingActionButton = findViewById(R.id.floatingActionButton)
        f.setOnClickListener()
        {
            var i = Intent(this, MainActivity2::class.java)
            startActivity(i)
        }
    }
}
5)activity lifecycle
@SuppressLint("MissingInflatedId")
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        enableEdgeToEdge()
        setContentView(R.layout.activity_main)
        Toast.makeText(applicationContext,"ONCREATE() CALLED",Toast.LENGTH_SHORT).show()
    }
    override fun onStart() {
        super.onStart()
        Toast.makeText(applicationContext,"ONSTART() CALLED",Toast.LENGTH_SHORT).show()
    }
    override fun onRestart() {
        super.onRestart()
        Toast.makeText(applicationContext,"ONRESTART() CALLED",Toast.LENGTH_SHORT).show()
    }
    override fun onResume() {
        super.onResume()
        Toast.makeText(applicationContext,"ONRESUME() CALLED",Toast.LENGTH_SHORT).show()
    }
    override fun onPause() {
        super.onPause()
        Toast.makeText(applicationContext,"ONPAUSE() CALLED",Toast.LENGTH_SHORT).show()
    }
    override fun onStop() {
        super.onStop()
        Toast.makeText(applicationContext,"ONSTOP() CALLED",Toast.LENGTH_SHORT).show()
    }
    override fun onDestroy() {
        super.onDestroy()
        Toast.makeText(applicationContext,"ONDESTROY() CALLED",Toast.LENGTH_SHORT).show()
    }
}
6)copy and paste
setContentView(R.layout.activity_main)
        val button:Button=findViewById(R.id.button)
        val et:EditText=findViewById(R.id.editTextText)
        val tv:TextView=findViewById(R.id.textView)
 
        button.setOnClickListener{
            tv.text=et.text.toString()
            Toast.makeText(this,"Text Copied",Toast.LENGTH_LONG).show()
        }
    }
}
7)hello world
<TextView
        android:id="@+id/textView3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:ems="10"
        android:inputType="textPersonName"
        android:minHeight="48dp"
        android:textAllCaps="true"
        android:textColor="#289428"
        android:text="MAD LAB"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.5" />
8)implicit intent
//implicit
        val url = "https://www.google.com"
        val implicitButton : FloatingActionButton = findViewById(R.id.floatingActionButton)
        implicitButton.setOnClickListener{
            val implicitIntent =Intent(Intent.ACTION_VIEW, Uri.parse(url))
            startActivity(implicitIntent)
        }
    }
}
9)login module
setContentView(R.layout.activity_main)
 
        userET = findViewById(R.id.editTextText3)
        passET = findViewById(R.id.editTextText4)
        loginBtn =findViewById(R.id.button3)
        loginBtn.setOnClickListener {
 
            if(userET.text.toString()=="cvr" && passET.text.toString()=="cvr123")
            {
                val intent= Intent(this,MainActivity2::class.java)
                intent.putExtra("Username",userET.text.toString())
                intent.putExtra("Password",passET.text.toString())
                startActivity(intent)
                Toast.makeText(this,"login success",Toast.LENGTH_LONG).show()
            }
            else
            {
                Toast.makeText(this,"error login ",Toast.LENGTH_LONG).show()
            }
        }
 
 
 
    }
}