打開activity的方法有以下幾種：

1. 使用顯式Intent打開目標Activity：

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

2. 使用隱式Intent打開目標Activity：

Intent intent = new Intent();
intent.setAction("com.example.ACTION_TARGET_ACTIVITY");
startActivity(intent);

3. 使用Intent傳遞數據到目標Activity：

Intent intent = new Intent(CurrentActivity.this, TargetActivity.class);
intent.putExtra("key", value);
startActivity(intent);

4. 使用startActivityForResult()方法打開目標Activity，并獲取返回結果：

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

5. 使用FLAG_ACTIVITY_NEW_TASK標記打開目標Activity：

Intent intent = new Intent(CurrentActivity.this, TargetActivity.class);
intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(intent);

6. 使用PendingIntent打開目標Activity：

Intent intent = new Intent(CurrentActivity.this, TargetActivity.class);
PendingIntent pendingIntent = PendingIntent.getActivity(CurrentActivity.this, requestCode, intent, PendingIntent.FLAG_UPDATE_CURRENT);
pendingIntent.send();