数据库课设(一)

public List getDeptInfo(){
	String sql = "select * from department";
	PreparedStatement psmt=null;
	List list = new ArrayList();
	try {
		psmt = conn.prepareStatement(sql);
		ResultSet rs = psmt.executeQuery();
		Department dept = null;
		while(rs.next()){
			dept.setDeptId(rs.getInt("DeptId"));
			dept.setDeptName(rs.getString("DeptName"));
			list.add(dept);
		}
	} catch (SQLException e) {
		// TODO Auto-generated catch block
		e.printStackTrace();
	}
	return list;
}

因为每一次循环都要把dept放到list里面，也就是list.add(dept);
所以每次循环开始都要新实例化一个dept,dept = new Department();这样就不会报空指针错误了。

public List getDeptInfo(){
	String sql = "select * from department";
	PreparedStatement psmt=null;
	List list = new ArrayList();
	try {
		psmt = conn.prepareStatement(sql);
		ResultSet rs = psmt.executeQuery();
		Department dept;
		while(rs.next()){
			dept = new Department();
			dept.setDeptId(rs.getInt("DeptId"));
			dept.setDeptName(rs.getString("DeptName"));
			list.add(dept);
		}
	} catch (SQLException e) {
		// TODO Auto-generated catch block
		e.printStackTrace();
	}
	return list;
}