Android开发startActivityForResult()弃用，推荐使用registerForActivityResult()方法

SecondActivity中

public class SecondActivity extends AppCompatActivity {
    private static final String TAG = "SecondActivity";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second);
        Button btnQuit = findViewById(R.id.btnQuit);
        btnQuit.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Log.d(TAG, "onClick: ");
                Intent intent = new Intent();
                intent.putExtra("data_return", "返回的数据");
                setResult(RESULT_OK, intent);
                finish();
            }
        });
    }
}

MainActivity中

ActivityResultLauncher launcher = registerForActivityResult(new ActivityResultContracts.StartActivityForResult(), new ActivityResultCallback<ActivityResult>() {
            @Override
            public void onActivityResult(ActivityResult result) {
                if (result.getResultCode() == RESULT_OK) {
                    Log.d(TAG, "onActivityResult: data = " + result.getData().getStringExtra("data_return"));
                }
            }
        });

        btnSecond.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(FirstActivity.this, SecondActivity.class);
               startActivityForResult(intent, 1);
                launcher.launch(intent);