爲什麼訪問$ 300（）在我的私人內部類中被調用？

客戶端正在通過Tomcat運行Web應用程序，並在看似無害的區域中發生異常的NullPointerException。正如您所看到的，NullPointerException不能出現在內部類BookingDetail的構造函數中。這是什麼訪問$ 300（）方法，它將如何被稱爲？是的，非常煩人，我沒有線路號碼，但我無法複製這個問題。

下面是代碼從LeaveCalculator類片段：

private class BookingDetail { 
    private Date from; 
    private Date upto; 
    private String wpat; 
    private String pubh; 
    private BookingDetail(Date from, Date upto, String wpat, String pubh) { 
     this.from = from; 
     this.upto = upto; 
     this.wpat = wpat; 
     this.pubh = pubh; 
    } 
} 

private void calculatePayHoursAndLeaveHoursForLSLHours(Date from, Date upto) { 
    String pubhMaster = ((LSLLeave) leave).getPublicHoliday().trim(); 
    List<PositionHistory> histories = findHistories(from, upto); 
    Map<Integer, BookingDetail> table = new HashMap<Integer, BookingDetail>(); 
    for (PositionHistory h : histories) { 
     BookingDetail position = table.get(h.getEmployment()); 
     if (position == null) { 
      table.put(h.getEmployment(), new BookingDetail(h.getFromDate(), h.getUpToDate(), h.getWorkPatternCode(), pubhMaster.isEmpty() ? h.getPublicHolidayCode() : pubhMaster)); 
     } else { 
      if (position.from.after(h.getFromDate())) 
       position.from = h.getFromDate(); 
      if (position.upto.before(h.getUpToDate())) 
       position.upto = h.getUpToDate(); 
     }  
    } 
    double payHoursTotal = 0; 
    double leaveHoursTotal = 0; 
    boolean error = false; 
    Set<Integer> keys = table.keySet(); 
    for (Integer employment : keys) { 
     BookingDetail row = table.get(employment); 
     if (row.from.before(from)) 
      row.from = from; 
     if (row.upto.after(upto)) 
      row.upto = upto; 
     calculatePayHoursAndLeaveHours(row, false); 
     error |= !verifyLeaveHours(); 
     payHoursTotal += payHours; 
     leaveHoursTotal += leaveHours; 
    } 
    leaveHours = error ? WORK_PATTERN_ERROR : leaveHoursTotal; 
    payHours = payHoursTotal; 
    BookingDetail lowestEmployment = table.get(employment); 
    wpat = lowestEmployment.wpat; 
    pubh = lowestEmployment.pubh; 
}

這裏是堆棧跟蹤：

java.lang.NullPointerException 
    at com.empower.ess.logic.leave.LeaveCalculator$BookingDetail.access$300(Unknown Source) 
    at com.empower.ess.logic.leave.LeaveCalculator.calculatePayHoursAndLeaveHoursForLSLHours(Unknown Source) 
    at com.empower.ess.logic.leave.LeaveCalculator.calculatePayHoursAndLeaveHours(Unknown Source) 
    at com.empower.ess.logic.leave.LeaveCalculator.calculateAmountToDisplay(Unknown Source) 
    at com.empower.ess.logic.leave.LeaveCalculator.calculateAmountToDisplay(Unknown Source) 
    at com.empower.ess.logic.leave.dwr.LeaveTypesLookup.calculateAmount(Unknown Source) 
    at sun.reflect.GeneratedMethodAccessor1190.invoke(Unknown Source) 
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) 
    at java.lang.reflect.Method.invoke(Method.java:597) 
    at com.empower.mawson.core.web.dwr.impl.ExecuteQuery.execute(ExecuteQuery.java:236) 
    at com.empower.mawson.core.web.dwr.impl.DefaultExecProcessor.handle(DefaultExecProcessor.java:44) 
    at com.empower.mawson.core.web.dwr.impl.DefaultProcessor.handle(DefaultProcessor.java:79) 
    at com.empower.mawson.core.web.dwr.AbstractDWRServlet.doPost(AbstractDWRServlet.java:151) 
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:647) 
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729) 
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:269) 
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188) 
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213) 
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:172) 
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127) 
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:117) 
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:108) 
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:174) 
    at org.apache.coyote.ajp.AjpAprProcessor.process(AjpAprProcessor.java:444) 
    at org.apache.coyote.ajp.AjpAprProtocol$AjpConnectionHandler.process(AjpAprProtocol.java:472) 
    at org.apache.tomcat.util.net.AprEndpoint$Worker.run(AprEndpoint.java:1286) 
    at java.lang.Thread.run(Thread.java:619)

來源

2012-02-06 mekazu

「訪問$ 300（）」調用是一種合成方法，其使訪問私有成員，這裏可能是「from」，「upto」，「wpat」或「pubh」。循環遍歷for-each循環時，其中一個可能爲null。例如，您需要驗證「row.from」是否爲空，然後再解除引用。

來源

2012-02-06 04:26:57 colbadhombre

謝謝，我認爲NullPointerException只會拋出'at at com.empower.ess.logic.leave.LeaveCalculator.calculatePayHoursAndLeaveHoursForLSLHours（Unknown Source）'，但考慮到在訪問BookingDetail專用時我沒有使用getters和setters成員這個答案是有道理的。 – mekazu 2012-02-06 04:40:28

爲什麼訪問$ 300（）在我的私人內部類中被調用？

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