要實現Android中列表項間的分隔線，可以通過自定義ItemDecoration來實現。以下是一個簡單的示例：

1. 首先創建一個自定義的ItemDecoration類，例如DividerItemDecoration：

public class DividerItemDecoration extends RecyclerView.ItemDecoration {
    private Drawable divider;

    public DividerItemDecoration(Context context, int resId) {
        divider = ContextCompat.getDrawable(context, resId);
    }

    @Override
    public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
        int left = parent.getPaddingLeft();
        int right = parent.getWidth() - parent.getPaddingRight();

        for (int i = 0; i < parent.getChildCount() - 1; i++) {
            View child = parent.getChildAt(i);
            RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child.getLayoutParams();
            int top = child.getBottom() + params.bottomMargin;
            int bottom = top + divider.getIntrinsicHeight();
            divider.setBounds(left, top, right, bottom);
            divider.draw(c);
        }
    }
}

2. 在RecyclerView的Adapter中設置DividerItemDecoration：

RecyclerView recyclerView = findViewById(R.id.recyclerView);
recyclerView.addItemDecoration(new DividerItemDecoration(this, R.drawable.divider));

3. 創建分隔線的drawable資源文件divider.xml：

<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle">
    <size android:height="1dp"/>
    <solid android:color="@color/divider_color"/>
</shape>

通過以上步驟，就可以實現在RecyclerView中為列表項添加分隔線了。如果想要自定義分隔線的樣式，可以修改DividerItemDecoration中的onDraw方法和divider.xml中的shape屬性。