안드로이드 액티비티 간의 단방향 데이터 전달

package com.minui.data;

import androidx.activity.result.ActivityResult;
import androidx.activity.result.ActivityResultCallback;
import androidx.activity.result.ActivityResultLauncher;
import androidx.activity.result.contract.ActivityResultContract;
import androidx.activity.result.contract.ActivityResultContracts;
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 {

    EditText editEmail;
    EditText editName;
    EditText editAge;
    Button button;

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

        editEmail = findViewById(R.id.editEmail);
        editName = findViewById(R.id.editAge);
        editAge = findViewById(R.id.editAge);
        button = findViewById(R.id.button);

        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                String email = editEmail.getText().toString().trim();
                String name = editName.getText().toString().trim();
                String ageStr = editAge.getText().toString().trim();

                int age = Integer.valueOf(ageStr).intValue();

                double hiddenData = 3.1414;

                // 새로운 액티비티를 띄우고,
                // 데이터를 전달한다.
                Intent intent = new Intent(MainActivity.this, SecondActivity.class);
                intent.putExtra("email",email);
                intent.putExtra("name", name);
                intent.putExtra("age", age);
                intent.putExtra("hidden", hiddenData);

                // 데이터만 전달하는 경우
                startActivity(intent);

            }
        });
    }
}

package com.minui.data;

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;
import android.widget.TextView;

public class SecondActivity extends AppCompatActivity {

    TextView txtEmail;
    TextView txtName;
    EditText editAge;
    Button button;

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

        // 넘어오는 데이터가 있으면 처리해 준다.
        String email = getIntent().getStringExtra("email");
        String name = getIntent().getStringExtra("name");
        int age = getIntent().getIntExtra("age", 0);
        double hiddenData = getIntent().getDoubleExtra("hidden", 0);

        // 화면과 연결
        txtEmail = findViewById(R.id.txtEmail);
        txtName = findViewById(R.id.txtName);
        editAge = findViewById(R.id.editAge);
        button = findViewById(R.id.button);

        // 데이터를 화면에 셋팅!!!!
        txtEmail.setText(email);
        txtName.setText(name);
        editAge.setText(age + "");

    }
}

Intent 객체에 putExtra(키,밸류)로 설정하고 받는 액티비티에서 getIntent().get타입Extra(키)로 받는다.