将对象[]传递给参数object[]在Java中不起作用

Question

我知道这个问题类似于将对象[]传递给params对象[]不工作，但是我在Java中遇到了类似的问题。

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);
}

我有一种感觉，这个问题是由传递一个对象内部的对象引起的，但我不确定如何解决这个问题，因为我对Java还是有点陌生。我试图做对象[]铸造，但它似乎没有工作。

我得到的错误是java.lang.NullPointerException

我已经返回objSingleTableColumns使用Arrays.toString(objSingleTableColumns)，它输出列列表如预期的没有问题…

为了明确db.dbShowColumns()的作用，它根据提供的表名返回一个数据库列名对象。

---

:我尝试像@Mansuro建议的那样初始化数组，但这不起作用。我做了一个测试运行来得到输出，也许可以解决这个问题。

是否有可能，我的代码正在创建一个多维数组，因为我正在传递一个对象[]到另一个对象[]?如果是这样的话有没有办法合并这些对象呢?因为我自己运行了this.buildSingleModel，它工作得很好。

---

此输出未运行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]

上面输出的代码是:

   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);

}
}

下面是运行this.buildSingleModel

时的输出

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可能是空的调用中的一个循环内。Arrays.toString()接受null，所以它可以正常工作。

Answer 2

必须初始化数组

objSingleTableColumns = new Object[ARRAY_SIZE];