public void setupLoadReaderTask() { if (task != null) { task.cancel(true); } if (RfApplication.readers == null) { RfApplication.readers = new Readers(this, ENUM_TRANSPORT.ALL); } task = new AsyncTask<Void, String, String>() { @Override protected synchronized String doInBackground(Void... voids) { InvalidUsageException hj = null; if (isCancelled()) { return null; } if (RfApplication.readers == null) { return null; } publishProgress("readers.GetAvailableRFIDReaderList()"); if (isCancelled()) { return null; } List<ReaderDevice> list = null; list = RfApplication.readers.GetAvailableRFIDReaderList(); if (hj != null){ RfApplication.readers.Dispose(); RfApplication.readers = null; if (RfApplication.readers == null) { RfApplication.readers = new Readers(getApplicationContext(), ENUM_TRANSPORT.BLUETOOTH); } } if (list == null || list.isEmpty()) { return null; } publishProgress("device.getRFIDReader()"); if (isCancelled()) { return null; } for (ReaderDevice readerDevice : list) { RfApplication.device = readerDevice; RfApplication.deviceName = readerDevice.getName(); Log.d("deviceName", readerDevice.getName()); RfApplication.reader = RfApplication.device.getRFIDReader(); // Log.d("地址：",readerDevice.getAddress()); if (RfApplication.reader.isConnected()) { return null; } publishProgress("reader.connect()"); if (isCancelled()) { return null; } try { RfApplication.reader.connect(); isStarted = true; configureReader(); } catch (InvalidUsageException | OperationFailureException e) { } if (RfApplication.reader.isConnected()) { break; } } if (!RfApplication.reader.isConnected()) { return null; } if (RfApplication.device.getName().startsWith("RFD8500") || RfApplication.device.getName().startsWith("RFD40")) { try { RfApplication.reader.Config.setBeeperVolume(BEEPER_VOLUME.QUIET_BEEP); RfApplication.reader.Config.setTriggerMode(ENUM_TRIGGER_MODE.BARCODE_MODE,false); RfApplication.reader.Config.setTriggerMode(ENUM_TRIGGER_MODE.RFID_MODE,true); } catch (InvalidUsageException | OperationFailureException e) { } } return String.format(getString(R.string.connect), RfApplication.device.getName().substring(0,RfApplication.device.getName().length()-14)); } @Override protected void onProgressUpdate(String... values) { } @Override protected void onPostExecute(String s) { if (s == null) { if (isStarted == false){ setupRetryDialog(); } } else { CustomToast.showLoad(HomeActivity.this,s,2000); } } @Override protected void onCancelled() { RfApplication.reader = null; RfApplication.readers = null; CustomToast.showToast(HomeActivity.this,getString(R.string.no_reader),2000); } }; task.execute(); }com.zebra.rfid.api3.InvalidUsageExceptionat com.ives.upcrfid_zebra.HomeActivity$12.doInBackground(HomeActivity.java:519)at com.ives.upcrfid_zebra.HomeActivity$12.doInBackground(HomeActivity.java:504)怎么解决

public ListNode addTwoNumbers(ListNode l1, ListNode l2) { ListNode head =null, tail =null; int carry =0; while(l1 != null && l2 != null){ //取出元素 //计算总和 //创建新节点 //把新节点链接在tail后 //更新tail //更新 l1 l2 int num1 = l1!=null?l1.val:0; int num2 = l2!=null?l2.val:0; int sum = num1+num2+carry; if(head == null){ head = tail =new ListNode(sum%10); }else{ tail.next =new ListNode(sum%10); } tail = tail.next; if(l1 != null) l1 = l1.next; if(l2 != null) l2 = l2.next; carry = sum/10; } return head; }请帮我看一下这段代码有问题吗

if (head == null) { head = tail = node; } else { tail.next = node; tail = tail.next; } if (l1 != null) l1 = l1.next; if (l2 != null) l2 = l2.next; } if (carry > 0) { tail.next = new ...

/** * Definition for singly-linked list. * public class ListNode { * int val; * ListNode next; * ListNode() {} * ListNode(int val) { this.val = val; } * ListNode(int val, ListNode next) { this.val = val; this.next = next; } * } */ class Solution { public ListNode addTwoNumbers(ListNode l1, ListNode l2) { ListNode head =null, tail =null; int carry =0; while(l1 != null && l2 != null){ //取出元素 //计算总和 //创建新节点 //把新节点链接在tail后 //更新tail //更新 l1 l2 int num1 = l1!=null?l1.val:0; int num2 = l2!=null?l2.val:0; int sum = num1+num2+carry; if(head == null){ head = tail =new ListNode(sum%10); }else{ tail.next =new ListNode(sum%10); } tail = tail.next; if(l1 != null) l1 = l1.next; if(l2 != null) l2 = l2.next; carry = sum/10; } if (carry>0){ tail.next = new ListNode(carry); } return head;}}请问这段代码问什么报错NULL POINT EXCEPTION

if (head == null) { head = tail = node; } else { tail.next = node; tail = tail.next; } if (l1 != null) l1 = l1.next; if (l2 != null) l2 = l2.next; } if (carry > 0) { tail.next = new ...

请帮我解释下面这段代码 <select id="listByUser" resultType="com.yj.model.vo.EnrollByUserItemVO"> select cc.*, cc.course_start_time AS courseStartTimeMd, ub.id ubid, info.payment_status as payment_status, info.total_money as totalMoney, ccc.category_name, CASE WHEN cc.course_video is not null and cc.course_video != '' THEN 2 WHEN (SELECT count(1) FROM crs_course_class ccc2 WHERE cc.id = ccc2.course_id AND ccc2.data_flag = 1 AND ccc2.class_video IS NOT NULL and ccc2.class_video != '') > 0 THEN 2 ELSE 1 END AS courseType from user_course_enroll ub INNER JOIN crs_course cc ON ub.course_id = cc.id INNER JOIN crs_course_category ccc ON cc.course_category_id = ccc.id LEFT JOIN order_item item ON item.project_relevancy_id = ub.id LEFT JOIN order_info info ON item.info_id = info.id LEFT JOIN user_browse uu ON uu.user_id = ub.user_id and uu.course_id = ub.course_id and uu.data_flag = 1 where 1 = 1 <if test="(publicId != null and publicId != '' ) or ( userIds != null and userIds.size() != 0)"> and ( <if test="publicId != null and publicId != '' "> ub.public_id = #{publicId} </if> <if test="publicId != null and publicId != '' and userIds != null and userIds.size() != 0"> or ub.user_id IN <foreach collection="userIds" item="item" open="(" separator="," close=")" index="index"> #{item} </foreach> </if> <if test="(publicId == null or publicId == '') and userIds != null and userIds.size() != 0"> ub.user_id IN <foreach collection="userIds" item="item" open="(" separator="," close=")" index="index"> #{item} </foreach> </if> ) </if> <choose> <when test="query.paymentStateList != null and query.paymentStateList.size() != 0"> and ccc.data_flag = 1 </when> <otherwise> and ub.apply_type = 1 and ccc.data_flag = 1 and ub.data_flag = 1 and ub.verify_state = 1 and cc.data_flag = 1 </otherwise> </choose> <if test="query.shelfStatus !=null"> and cc.shelf_status = #{query.shelfStatus} </if> <if test="query.categoryId !=null and query.categoryId != ''"> and ccc.id = #{query.categoryId} </if> <if test="query.learnState !=null"> and uu.learn_state = #{query.learnState} and ccc.prelect_way = 1 </if> <if test="query.paymentStateList != null and query.paymentStateList.size() != 0"> AND ( info.payment_status IN <foreach collection="query.paymentStateList" item="item" open="(" separator="," close=")" index="index"> #{item} </foreach> ) </if> </select>

在条件中使用了 if 和 foreach 标签，根据不同的情况生成不同的查询条件。除此之外，查询语句中还使用了 choose 标签，根据不同的条件生成不同的查询条件，相当于 Java 中的 switch 语句。最后，查询语句中还...

优化以下代码，使其合法 public void OnClick() { Debug.Log("stand"); GameObject go = GameObject.Find("Constructor"); if (go != null) { Animation animation = go.GetComponent<Animation>; if (animation["idle"] != null) animation.Play("idle"); } }

public void OnClick() { Debug.Log("stand"); GameObject go = GameObject.Find("Constructor"); if (go != null) { Animation animation = go.GetComponent(); if (animation != null && animation["idle"]...

public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String method = request.getParameter("method"); System.out.println("method----> " + method); if(method != null && method.equals("add")){ //增加操作 this.add(request, response); }else if(method != null && method.equals("query")){ this.query(request, response); }else if(method != null && method.equals("getrolelist")){ this.getRoleList(request, response); }else if(method != null && method.equals("ucexist")){ this.userCodeExist(request, response); }else if(method != null && method.equals("deluser")){ this.delUser(request, response); }else if(method != null && method.equals("view")){ this.getUserById(request, response,"jsp/userview.jsp"); }else if(method != null && method.equals("modify")){ this.getUserById(request, response,"jsp/usermodify.jsp"); }else if(method != null && method.equals("modifyexe")){ this.modify(request, response); }else if(method != null && method.equals("pwdmodify")){ this.getPwdByUserId(request, response); }else if(method != null && method.equals("savepwd")){ this.updatePwd(request, response); } }

- 如果method不为null且等于"add"，则调用add方法进行增加操作。 - 如果method不为null且等于"query"，则调用query方法进行查询操作。 - 如果method不为null且等于"getrolelist"，则调用getRoleList方法获取角色...

public void OnClick() { Debug.Log("jump"); GameObject go = GameObject.Find("Constructor"); if (go != null) { Animation animation = go.GetComponent<Animation>(); if (animation["jump_pose"] != null) animation.Play("jump_pose"); } } 在以上代码中，我想做到名为jump_pose的动画播放完毕后，再执行animation.Play("idle")，该如何修改

public void OnClick() { StartCoroutine(PlayJumpAnimation()); } 在修改后的代码中，我们将播放跳跃动画的逻辑封装到一个协程函数 PlayJumpAnimation() 中。首先播放跳跃动画，然后通过 yield return new...

button1.addActionListener(new ActionListener() { @Override public void actionPerformed(ActionEvent e1) { String srcPath = null; String destPath = null; FileInputStream fis= null; FileOutputStream fos=null; try { //文件 File file=new File(srcPath); File file1=new File(destPath); //流 fis = new FileInputStream(file); fos=new FileOutputStream(file1); //读数据 byte[] buffer=new byte[1024]; int len; while((len=fis.read(buffer))!=-1){ fos.write(buffer,0,len); } } catch (IOException e) { e.printStackTrace(); } finally { //关闭流 try { if(fis!=null) fis.close(); } catch (IOException e) { e.printStackTrace(); } try { if(fos!=null) fos.close(); } catch (IOException e) { e.printStackTrace(); } } } } );点击button1实现已选择文件的拷贝，详细说说代码要怎么改

public void actionPerformed(ActionEvent e1) { // 创建文件选择器 JFileChooser chooser = new JFileChooser(); // 显示文件选择器对话框 int result = chooser.showOpenDialog(null); if (result == ...

@Override public boolean equals(Object that) { if (this == that) { return true; } if (that == null) { return false; } if (getClass() != that.getClass()) { return false; } ApartmentAdmin other = (ApartmentAdmin) that; return (this.getId() == null ? other.getId() == null : this.getId().equals(other.getId())) && (this.getUserName() == null ? other.getUserName() == null : this.getUserName().equals(other.getUserName())) && (this.getPassword() == null ? other.getPassword() == null : this.getPassword().equals(other.getPassword())) && (this.getRoleId() == null ? other.getRoleId() == null : this.getRoleId().equals(other.getRoleId())) && (this.getHeadimg() == null ? other.getHeadimg() == null : this.getHeadimg().equals(other.getHeadimg())) && (this.getPhone() == null ? other.getPhone() == null : this.getPhone().equals(other.getPhone())) && (this.getSex() == null ? other.getSex() == null : this.getSex().equals(other.getSex())) && (this.getBuildingNo() == null ? other.getBuildingNo() == null : this.getBuildingNo().equals(other.getBuildingNo())) && (this.getCreateTime() == null ? other.getCreateTime() == null : this.getCreateTime().equals(other.getCreateTime())) && (this.getIsLock() == null ? other.getIsLock() == null : this.getIsLock().equals(other.getIsLock())); }请详细解释每一行代码

5. 第五行 if (that == null) 判断传入的对象是否为 null，如果是，则直接返回 false，表示两个对象不相等。 6. 第六行 if (getClass() != that.getClass()) 判断传入的对象是否属于当前对象所属的类，如果不是，则...

public class FloorSetter : MonoBehaviour { public GameObject floorOnRunning; public GameObject floorForward; public static FloorSetter instance; // Use this for initialization void Start () { instance = this; } void RemoveItem(GameObject floor) { var item = floor.transform.Find("Item"); { foreach (var child in item) { Transform childTransform = child as Transform; if (childTransform != null) { Destroy(childTransform.gameObject); } } } } void AddItem(GameObject floor) { var item = floor.transform.Find("Item"); if (item != null) { var patternManager = PatternManager.instance; if (patternManager != null && patternManager.Patterns != null && patternManager.Patterns.Count > 0) { var pattern = patternManager.Patterns[Random.Range(0, patternManager.Patterns.Count)];

这段代码是一个名为 FloorSetter 的类，它是用 C# 语言编写的，主要用于设置地板的一些属性和特效。该类中包含了一些公共变量，如 floorOnRunning 和 floorForward，它们分别代表地板上正在运行的物体和前方的...

public Object poll() { if(front!=null) { CarNode p=front; front=front.next; if(p==rear) rear=null; return p.car; } else return null; } public void display() { CarNode p=front; while(p!=null) { System.out.println(p.car+","); p=p.next; } } }详细解释这段代码

public void display() { CarNode p=front; // 从队头开始遍历 while(p!=null) { // 遍历直到队列末尾 System.out.println(p.car+","); // 打印当前节点的car属性 p=p.next; // 移动到下一个节点 } } 需要...

public List<AuthorityListVo> authorityList(List<AuthorityListVo> search, Date parameterEndTime, Date parameterBeginTime) { List<AuthorityListVo> authorityListVoList = new ArrayList<>(); for (AuthorityListVo authorityListVo : search) { Date beginTime = authorityListVo.getBeginTime(); Date endTime = authorityListVo.getEndTime(); if (parameterEndTime == null) { if (beginTime.compareTo(parameterBeginTime) >= 0 || endTime.compareTo(parameterBeginTime) >= 0) { authorityListVoList.add(authorityListVo); } } else if (parameterBeginTime == null && beginTime.compareTo(parameterEndTime) <= 0 || parameterBeginTime == null && endTime.compareTo(parameterEndTime) <= 0) { authorityListVoList.add(authorityListVo); } if (parameterEndTime != null && parameterBeginTime != null && beginTime.compareTo(parameterBeginTime) >= 0 && beginTime.compareTo(parameterEndTime) <= 0) { authorityListVoList.add(authorityListVo); } if (parameterEndTime != null && parameterBeginTime != null && endTime.compareTo(parameterBeginTime) >= 0 && endTime.compareTo(parameterEndTime) <= 0) { authorityListVoList.add(authorityListVo); } } return authorityListVoList; } 如何优化

public static void main(String[] args) { // 示例调用 List<AuthorityListVo> search = new ArrayList(); LocalDate parameterBeginTime = LocalDate.of(2021, 1, 1); LocalDate parameterEndTime = ...

改写为连接SQl server数据库：package lemon.util; import com.mysql.cj.jdbc.MysqlDataSource; import lemon.exception.SystemException; import javax.sql.DataSource; import java.sql.Connection; import java.sql.ResultSet; import java.sql.SQLException; import java.sql.Statement; public class DBUtil { private static final String URL = "jdbc:sqlserver://localhost:1433;DatabaseName=book"; private static final String USERNAME = "sa"; private static final String PASSWORD = "123456"; private static volatile DataSource DATA_SOURCE; private DBUtil(){} private static DataSource getDataSource(){ if(DATA_SOURCE == null){ synchronized (DBUtil.class){ if(DATA_SOURCE == null){ DATA_SOURCE = new MysqlDataSource(); ((MysqlDataSource) DATA_SOURCE).setURL(URL); ((MysqlDataSource) DATA_SOURCE).setUser(USERNAME); ((MysqlDataSource) DATA_SOURCE).setPassword(PASSWORD); } } } return DATA_SOURCE; } public static Connection getConnection(){ try { return getDataSource().getConnection(); } catch (SQLException e) { throw new SystemException("000001", "获取数据库连接失败", e); } } public static void close(Connection c, Statement s){ close(c, s, null); } public static void close(Connection c, Statement s, ResultSet r){ try { if(r != null) r.close(); if(s != null) s.close(); if(c != null) c.close(); } catch (SQLException e) { throw new SystemException("000002", "释放数据库资源出错", e); } } }

public static void close(Connection c, Statement s, ResultSet r){ try { if(r != null) r.close(); if(s != null) s.close(); if(c != null) c.close(); } catch (SQLException e) { throw new ...

public void deleteNode(ListNode head, int i) { if (i == 0 || head == null) { return; } if (i == 1) { head = head.next; return; } ListNode prev = head; for (int j = 1; j < i - 1 && prev != null && prev.next != null; j++) { prev = prev.next; } if (prev == null || prev.next == null) { return; } prev.next = prev.next.next;}

1. 如果i为0或者head为null，则直接返回。 2. 如果i为1，则将head指向下一个节点即可，然后返回。 3. 如果i大于1，则需要遍历链表找到要删除节点的前一个节点prev。遍历过程中需要判断prev和prev.next是否为空，...

public boolean equals(Object obj) { if (this == obj) return true; if (obj == null) return false; if (getClass() != obj.getClass()) return false; Product other = (Product) obj; if (id == null) { if (other.id != null) return false; } else if (!id.equals(other.id)) return false; return true; }、

if (obj == null) return false; if (getClass() != obj.getClass()) return false; Product other = (Product) obj; if (id == null) { if (other.id != null) return false; } else if (!id.equals(other...

private void updateShowSeconds() { if (mShowSeconds) { // Wait until we have a display to start trying to show seconds. if (mSecondsHandler == null && getDisplay() != null) { mSecondsHandler = new Handler(); if (getDisplay().getState() == Display.STATE_ON) { mSecondsHandler.postAtTime(mSecondTick, SystemClock.uptimeMillis() / 1000 * 1000 + 1000); } IntentFilter filter = new IntentFilter(Intent.ACTION_SCREEN_OFF); filter.addAction(Intent.ACTION_SCREEN_ON); mContext.registerReceiver(mScreenReceiver, filter); } } else { if (mSecondsHandler != null) { mContext.unregisterReceiver(mScreenReceiver); mSecondsHandler.removeCallbacks(mSecondTick); mSecondsHandler = null; updateClock(); } } } private final BroadcastReceiver mScreenReceiver = new BroadcastReceiver() { @Override public void onReceive(Context context, Intent intent) { String action = intent.getAction(); if (Intent.ACTION_SCREEN_OFF.equals(action)) { if (mSecondsHandler != null) { mSecondsHandler.removeCallbacks(mSecondTick); } } else if (Intent.ACTION_SCREEN_ON.equals(action)) { if (mSecondsHandler != null) { mSecondsHandler.postAtTime(mSecondTick, SystemClock.uptimeMillis() / 1000 * 1000 + 1000); } } } }; private final Runnable mSecondTick = new Runnable() { @Override public void run() { if (mCalendar != null) { updateClock(); } mSecondsHandler.postAtTime(this, SystemClock.uptimeMillis() / 1000 * 1000 + 1000); } }; } Android4.4编译报错getDisplay().getState(

if (mSecondsHandler == null && getSystemService(Context.WINDOW_SERVICE).getDefaultDisplay() != null) { mSecondsHandler = new Handler(); if (getSystemService(Context.WINDOW_SERVICE)....

class Solution { public boolean isSameTree(TreeNode root, TreeNode subRoot) { if (p == null && q != null || p != null && q == null) { return false; } if (p == null && q == null) { return true; } if (p.val != q.val) { return false; } return isSameTree(p.left, q.left) && isSameTree(p.right, q.right); } }Char 11: error: expected ':' public boolean isSameTree(TreeNode root, TreeNode subRoot) 报了这个错误哪里有问题

if (root == null && subRoot == null) { return true; } if (root.val != subRoot.val) { return false; } return isSameTree(root.left, subRoot.left) && isSameTree(root.right, subRoot.right); } } ...

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优化以下代码，使其合法 public void OnClick() { Debug.Log("stand"); GameObject go = GameObject.Find("Constructor"); if (go != null) { Animation animation = go.GetComponent<Animation>; if (animation["idle"] != null) animation.Play("idle"); } }

public Object poll() { if(front!=null) { CarNode p=front; front=front.next; if(p==rear) rear=null; return p.car; } else return null; } public void display() { CarNode p=front; while(p!=null) { System.out.println(p.car+","); p=p.next; } } }详细解释这段代码

public boolean equals(Object obj) { if (this == obj) return true; if (obj == null) return false; if (getClass() != obj.getClass()) return false; Product other = (Product) obj; if (id == null) { if (other.id != null) return false; } else if (!id.equals(other.id)) return false; return true; }、

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