主活动启动后，如何转到具体活动？

Intent intent = new Intent(MainActivity.this, TargetActivity.class);
startActivity(intent);

Intent intent = new Intent("com.example.ACTION_TARGET");
intent.addCategory("android.intent.category.DEFAULT");
startActivity(intent);

Intent intent = new Intent(MainActivity.this, TargetActivity.class);
startActivityForResult(intent, REQUEST_CODE);

Intent resultIntent = new Intent();
resultIntent.putExtra("result", "Hello from TargetActivity");
setResult(RESULT_OK, resultIntent);
finish();

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    if (requestCode == REQUEST_CODE && resultCode == RESULT_OK) {
        String result = data.getStringExtra("result");
        // 处理返回结果
    }
}