小编Liv*_*ivy的帖子

首先,我已经知道FragmentManager经常会破坏然后使用默认构造函数重新创建Fragment.编码器必须在工厂方法中将重要事物保存在一组参数中,然后每次在onCreate(Bundle)中重新创建片段时将它们取出.

public class MyFragment extends Fragment {
    private static final String MY_STRING_CONSTANT = "param";
    private int mIntegerMember;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mIntegerMember= getArguments().getInt(MY_STRING_CONSTANT);
    }
}

我的问题是,这有什么区别:

// Inside MyFragment.java
public MyFragment() {
    // No-argument constructor required by the FragmentManager.
}
public static MyFragment newInstance(int param) {
    // Factory method
    MyFragment fragment = new MyFragment();
    Bundle args = new Bundle();
    args.putInt(MY_STRING_CONSTANT, param);
    fragment.setArguments(args);
    return fragment;
}

// Somewhere else
FragmentTransaction transaction = getFragmentManager().beginTransaction();
transaction.add(R.id.frame_layout, MyFragment.newInstance(123)).commit();

还有这个: …

下面是我写过的第一个Java泛型:

public class MyClass {

    public static <T> T castToAnotherType(Object param) {
        T ret = null;
        try {
            ret = (T) param;
        } catch (ClassCastException e) {
            System.out.print("Exception inside castToAnotherType()");
        }
        return ret;
    }

    public static void main(String[] args) {
        try {
            String obj = MyClass.castToAnotherType(new Object());
        } catch (ClassCastException e) {
            System.out.print("Exception outside castToAnotherType()");
        }
    }

}

结果是"castToAnotherType()之外的异常".为什么在泛型方法中不会发生异常？

我注意到使用 VSCode 终端时缺少很多命令。ls -l /所以我在我的发行版和 VSCode 的终端上都尝试了。

Linux Mint Xfce 终端：

livy@linux-mint:~$ ls -l /
total 2097252
drwxr-xr-x   2 root root       4096 Aug 13 15:13 bin
drwxr-xr-x   4 root root       4096 Aug 13 15:15 boot
drwxr-xr-x   2 root root       4096 Aug 13 15:06 cdrom
drwxr-xr-x  20 root root       4260 Aug 15 08:40 dev
drwxr-xr-x 147 root root      12288 Aug 13 16:46 etc
drwxr-xr-x   4 root root       4096 Aug 13 15:06 home
lrwxrwxrwx   1 root root         33 Aug 13 …