How to use putExtra || getIntentExtra in Java

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First Application Code where we use putExtra:

package com.example.todayclasspratice;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

public class MainActivity extends AppCompatActivity {


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

        EditText FirstName1=findViewById(R.id.FirstName);
        EditText LastName2=findViewById(R.id.LastName);
        EditText nickName3=findViewById(R.id.nickName);
        Button btn=findViewById(R.id.btn);

        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String FirstName,LastName,nickName;
                
                FirstName=FirstName1.getText().toString();
                LastName=LastName2.getText().toString();
                nickName=nickName3.getText().toString();
                
                Intent a=new Intent(MainActivity.this,MainActivity2.class);
                
                a.putExtra("FirstName",FirstName);
                a.putExtra("LastName",LastName);
                a.putExtra("nickName",nickName);
                startActivity(a);

            }
        });
    }
}

Second Application Code where we use getIntent || getStringExtra:

package com.example.todayclasspratice;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.widget.TextView;

public class MainActivity2 extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);
        TextView txt1,txt2,txt3;

        txt1=findViewById(R.id.text1);
        txt2=findViewById(R.id.textView2);
        txt3=findViewById(R.id.text3);

        String a,b,c;

        a=getIntent().getStringExtra("FirstName");
        b=getIntent().getStringExtra("LastName");
        c=getIntent().getStringExtra("nickName");

        txt1.setText(a);
        txt2.setText(b);
        txt3.setText(c);

    }
}