在Java中無法將object []傳遞給參數object []

Question

我知道這個問題類似於將object []傳遞給params object []不起作用，但是我在Java中也遇到了類似的問題。

try {
  Object[] objSingleTableColumns = null;
  DatabaseActions db = new DatabaseActions();
  db.dbConnect(sDatabase);
  for (int i=0 ; i < objTableList.length; i++) {
    objSingleTableColumns = db.dbShowColumns(objTableList[i].toString());
    this.buildSingleModel(objTableList[i].toString(), sDatabase, objSingleTableColumns, false);
  }
  db.dbClose();
} catch (Exception e) {
  System.out.println("Error with Multiple Columns" + e);
}

我感覺到問題是由於傳遞對象內部的對象引起的，但是由於我對Java還是有點陌生​​，所以我不確定如何解決此問題。我嘗試進行Object [] Casting，但確實做到了似乎不起作用。

我得到的錯誤是java.lang.NullPointerException

我已經使用Arrays.toString(objSingleTableColumns)返回了objSingleTableColumns ，它按預期輸出了列列表，沒有問題...

為了闡明db.dbShowColumns()作用，它根據提供的表名返回數據庫列名的對象。

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更新 ：我嘗試按照@Mansuro的建議初始化數組，但這沒有用。 我進行了一次測試，以獲得可能解決此問題的輸出。

因為將Object []傳遞到另一個Object []中，我的代碼是否可能創建多維數組？ 如果是這樣，是否有合並對象的方法？ 因為我自己運行了this.buildSingleModel ，所以效果很好。

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此輸出未運行this.buildSingleModel

objTableList = [glossary, messages, prodfeatures, renters, source, test_table]
objTableList.length = 6
objSingleTableColumns = [gid, gname, gmeaning]
objSingleTableColumns = [mid, msubject, mtype, mread, mcid, mmessage, mtimedate, mproduct, mstar]
objSingleTableColumns = [fid, fpid, ftext, ftype, fsort, fonline]
objSingleTableColumns = [rid, fname, lname, phone, email]
objSingleTableColumns = [sid, sw]
objSingleTableColumns = [tid, tname, tdesc]

以上輸出的代碼是：

   public void  buildMultipleModels(String sDatabase, Object[] objTableList)  {


try {

      Object[] objSingleTableColumns = new Object[100];

      DatabaseActions db = new DatabaseActions();
      db.dbConnect(sDatabase);


       System.out.println("objTableList = " + Arrays.toString(objTableList));
       System.out.println("objTableList.length = " + objTableList.length);

      for (int i=0 ; i < objTableList.length; i++) {
            objSingleTableColumns = db.dbShowColumns(objTableList[i].toString());

            System.out.println("objSingleTableColumns = " + Arrays.deepToString(objSingleTableColumns));

           // this.buildSingleModel(objTableList[i].toString(), sDatabase, objSingleTableColumns, false);
      }
      db.dbClose();


} catch (Exception e) {

   System.out.println("Error with Multiple Columns --> Exception =" + e);

    StringWriter sw = new StringWriter();
    new Throwable("").printStackTrace(new PrintWriter(sw));
    String stackTrace = sw.toString();


   System.out.println("Stack trace = " + stackTrace);


}
}

這是運行this.buildSingleModel的輸出

objTableList = [glossary, messages, prodfeatures, renters, source, test_table]
objTableList.length = 6
objSingleTableColumns = [gid, gname, gmeaning]
Error with Multiple Columns --> Exception =java.lang.NullPointerException
Stack trace = java.lang.Throwable: 
        at genModel.buildMultipleModels(genModel.java:170)
        at genModel.doBuildMultipleModels(genModel.java:67)
        at frmMain.btnGenerateMultipleModelsActionPerformed(frmMain.java:530)
        at frmMain.access$600(frmMain.java:44)
        at frmMain$7.actionPerformed(frmMain.java:322)
        at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
        at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
        at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
        at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
        at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
        at java.awt.Component.processMouseEvent(Component.java:6267)
        at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
        at java.awt.Component.processEvent(Component.java:6032)
        at java.awt.Container.processEvent(Container.java:2041)
        at java.awt.Component.dispatchEventImpl(Component.java:4630)
        at java.awt.Container.dispatchEventImpl(Container.java:2099)
        at java.awt.Component.dispatchEvent(Component.java:4460)
        at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4577)
        at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4238)
        at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4168)
        at java.awt.Container.dispatchEventImpl(Container.java:2085)
        at java.awt.Window.dispatchEventImpl(Window.java:2478)
        at java.awt.Component.dispatchEvent(Component.java:4460)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

Answer 1

似乎objSingleTableColumns對於for循環內的調用之一可能為null。 Arrays.toString（）接受null，因此可以正常工作。 這只是猜測，因為未提供堆棧跟蹤。

Answer 2

您必須初始化數組

objSingleTableColumns = new Object[ARRAY_SIZE];