MainActivity.java

package io.github.aleksandarharalanov.registrationapp;

import androidx.appcompat.app.AppCompatActivity;
import android.content.Intent;
import android.os.Bundle;
import android.text.Editable;
import android.text.TextWatcher;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

public class MainActivity extends AppCompatActivity {

    private EditText editText;
    private Button button;

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

        editText = findViewById(R.id.editTextText);
        button = findViewById(R.id.button);

        editText.addTextChangedListener(new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {}

            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {
                String name = s.toString().trim();
                boolean isValidName = name.length() >= 3 && name.length() <= 100;
                button.setEnabled(isValidName);
            }

            @Override
            public void afterTextChanged(Editable s) {}
        });

        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String name = editText.getText().toString().trim();
                Intent intent = new Intent(MainActivity.this, RegistrationDetailsActivity.class);
                intent.putExtra("registrantName", name);
                startActivity(intent);
            }
        });
    }
}