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for a larg-DB based dynamically-multiple-area-menu, I created a class MenuPoint:

class MenuPoint{
public int areaId;

public int preID;

public String name;
public String desc;

public String stepInImg = "bsp.img";
public String stepOutImg = "bsp.img";

public String detailedForm = "bsp.fxml";
public String detailedImg = "bsp.img";

public String [] additionalOptionForm = new String[0];
public String [] additionalOptionName = new String[0];
public String [] additionalOptionImg = new String[0];}

and initialised it as an 0-length array in my main class: MenuController
public MenuPoint [] menuItem = new MenuPoint[0];

I use a API call to get my DB stored information by initialisation of MenuController. I store the results by using the following code:

int dataStructlength = 12;
    String[] exampleApiResultKeys = new String[dataStructlength];
    exampleApiResultKeys[0] = "SITE_NUMBER";
    exampleApiResultKeys[1] = "SITE_DESC";
    exampleApiResultKeys[2] = "SITE_NUMBER_EXT";
    exampleApiResultKeys[3] = "CELL_NUMBER";
    exampleApiResultKeys[4] = "CELL_DESC";
    exampleApiResultKeys[5] = "CELL_TYPE";
    exampleApiResultKeys[6] = "MACHINE_GROUP_NUMBER";
    exampleApiResultKeys[7] = "MACHINE_GROUP_DESC";
    exampleApiResultKeys[8] = "MACHINE_GROUP_TYPE";
    exampleApiResultKeys[9] = "STATION_NUMBER";
    exampleApiResultKeys[10] = "STATION_DESC";
    exampleApiResultKeys[11] = "STATION_TYPE";

    exampleApiController.test_mdataGetMachineAssetStructure(exampleApiFilter, exampleApiResultKeys);

    for(int i = 0; exampleApiController.resultValues.value != null && i < exampleApiController.resultValues.value.length/12; i++)
    {
        boolean isUseless = false;
        for(int a = 0; a < dataStructlength; a ++)
            if(true == exampleApiController.resultValues.value[i*dataStructlength+a].trim().isEmpty())
                isUseless = true;

        if(!isUseless)
        {
        int preId= -1;
        if("M".equals(exampleApiController.resultValues.value[i*12+5]))
        {
            if(giveItemId(0, preId, exampleApiController.resultValues.value[i*12]) >= 0)
                preId = giveItemId(0, preId, exampleApiController.resultValues.value[i*12]);
            else
                preId = addMenuItem(0, preId, exampleApiController.resultValues.value[i*12], exampleApiController.resultValues.value[i*12+1], "bsp.form");
        }
        if("M".equals(exampleApiController.resultValues.value[i*12+5]))
        {
            if(giveItemId(1, preId, exampleApiController.resultValues.value[i*12+3]) >= 0)
                preId = giveItemId(0, preId, exampleApiController.resultValues.value[i*12+3]);
            else
                preId = addMenuItem(1, preId, exampleApiController.resultValues.value[i*12+3], exampleApiController.resultValues.value[i*12+4], "bsp.form");
        }
        if("M".equals(exampleApiController.resultValues.value[i*12+8]))
        {
            if(giveItemId(2, preId, exampleApiController.resultValues.value[i*12+6]) >= 0)
                preId = giveItemId(0, preId, exampleApiController.resultValues.value[i*12+6]);
            else
                preId = addMenuItem(2, preId, exampleApiController.resultValues.value[i*12+6], exampleApiController.resultValues.value[i*12+7], "bsp.form");
        }
        if("M".equals(exampleApiController.resultValues.value[i*12+11]))
        {
            if(giveItemId(3, preId, exampleApiController.resultValues.value[i*12+9]) >= 0)
                preId = giveItemId(0, preId, exampleApiController.resultValues.value[i*12+9]);
            else
                preId = addMenuItem(3, preId, exampleApiController.resultValues.value[i*12+9], exampleApiController.resultValues.value[i*12+10], "bsp.form");
        }
        }

giveItemId:

public int giveItemId(int areaId_temp, int preId_temp, String name_temp)
{
    for(int i = 0; i < menuItem.length; i++)
    {
        if(menuItem[i].areaId == areaId_temp && menuItem[i].name.equals(name_temp) &&  menuItem[i].preID == preId_temp)
            return i;
    }
    return -1;
}

addMenuItem:

public int addMenuItem(int areaId_temp, int preId_temp, String name_temp, String desc_temp, String form_temp)
{
    Object newArray1 = Array.newInstance(menuItem.getClass().getComponentType(), Array.getLength(menuItem)+1);  // +1 Arrayfeld
    System.arraycopy(menuItem, 0, newArray1, 0, Array.getLength(menuItem));
    menuItem = (MenuPoint[]) newArray1; // expend but missing attributes

    menuItem[menuItem.length-1].areaId = areaId_temp;
    menuItem[menuItem.length-1].preID = preId_temp;
    menuItem[menuItem.length-1].name = name_temp;
    menuItem[menuItem.length-1].desc = desc_temp;
    menuItem[menuItem.length-1].detailedForm = form_temp;
    return menuItem.length-1;
}

I found out that menuItem dons´t carry any attributes after expending it.

Do I have to create "new" Instances of MenuPoint to make it work? Is it even possible to expend a class-array without loosing attributes or their values? It shoud, because in the end menuItem is just a pointer-array, pointing on multiple workstorage-addresses, aren't it?

Thank you guys for any tips or better concept you can give me. (I know this class-concept is silly but I have no idea for a better one) And please excuse my bad grammar.

4

2 回答 2

1

您在方法 addMenuItem 中创建一个新数组，然后使用现有 menuItem 中的成员填充该数组，但索引（新）长度 - 1 处的元素未初始化：

menuItem[menuItem.length-1] = new MenuPoint();

尝试设置字段时，您应该得到 NullPointerException。

java.lang.reflect.Array 的所有这些用法都是相当做作的。有更简单的方法可以实现这一点。这是 addMenuItem 的简化版本

public int addMenuItem(int areaId, String name){
    MenuPoint[] newMenuItem = new MenuPoint[menuItem.length + 1];
    System.arraycopy(menuItem, 0, newMenuITem, 0, menuItem.length);
    menuItem = newMenuItem;
    menuItem[menuItem.length-1] = new MenuPoint();
    menuItem[menuItem.length-1].areaId = areaId;
    menuItem[menuItem.length-1].name = name;
    return menuItem.length; // Why -1 ? 
}

但是，最重要的是，一定要使用List<MenuPoint>.

于 2015-02-09T08:54:03.883 回答
1

对于你的问题的答案Do I have to create "new" Instances of MenuPoint to make it work?

Yes

从您的代码片段中，您需要初始化MenuPoint类对象以将其值存储到数组menuItem中。
用下面的行初始化你的数组元素 

menuItem[menuItem.length-1] = new MenuPoint();

复制数组后放在上面的行menuItem = (MenuPoint[]) newArray1;

如果没有初始化NullPointerException，将值设置为 null 对象会出现异常。

有一些更好的方法可以使用ArrayList类来维护对象列表。

要使用 ArrayList，您需要进行以下代码更改 

public List<MenuPoint> menuItem = new ArrayList<MenuPoint>; //Initialize list

你的功能将是 

public int addMenuItem(int areaId_temp, int preId_temp, String name_temp, String desc_temp, String form_temp)
    {
        MenuPoint menuPoint = new MenuPoint();

        menuPoint.areaId = areaId_temp;
        menuPoint.preID = preId_temp;
        menuPoint.name = name_temp;
        menuPoint.desc = desc_temp;
        menuPoint.detailedForm = form_temp;
        menuItem.add(menuPoint);

        return menuItem.size()-1;
    }

我认为这比在数组中使用反射要容易。

于 2015-02-09T08:56:52.863 回答