Question

我正在尝试连接两个数组以向数字数组的列添加标签，并在数组的最后一行之后添加总数。我在另一个Stack Overflow线程How can I concatenate two arrays in Java?上找到了一些代码。但是我收到了错误

线程中的异常＆＃34; AWT-EventQueue-0＆＃34; java.lang.ClassCastException： [Ljava.lang.Object;不能转换为[[Ljava.lang.Object;

这是我的代码

public void getpdf(double[][] pricelist, ArrayList<Piece> in) {
    PDDocument doc = new PDDocument();
    PDPage page = new PDPage();
    doc.addPage( page );
    try {
            PDPageContentStream contentStream =
                            new PDPageContentStream(doc, page);
            JTable table=gettable(pricelist,in);

            Object[] headercol={"Type","Asc","Ref","Commandes","Prix unitaire","Prix total"};
            Object[][] content=getTableData(table);
            Object[][] global=(Object[][]) concatenate (headercol,content);
            //drawTable(page, contentStream, 700, 75, headercol); 
            drawTable(page, contentStream, 700, 75, content); 
            contentStream.close();
            doc.save("bill.pdf" );
    }
    catch (IOException ex) {
        ex.printStackTrace();
    }

}   

public <T> T[] concatenate (T[] a, T[][] b) {
    int aLen = a.length;
    int bLen = b.length;

    @SuppressWarnings("unchecked")
    T[] c = (T[]) Array.newInstance(a.getClass().getComponentType(), aLen+bLen);
    System.arraycopy(a, 0, c, 0, aLen);
    System.arraycopy(b, 0, c, aLen, bLen);

    return c;
}

Answer 1

public <T> T[] concatenate (T[] a, T[][] b)

您无法连接两个不同类型的数组。 a是T s的数组，b是T[] s的数组，即它是T s的数组数组。

Answer 2

您似乎想要连接T[] a标头和T[][] b内容，但您的concatenate方法会返回T[]。您必须返回T[][]，即创建一个a.getClass()而不是a.getClass().getComponentType()的数组。此外，在新的T[][] c中，T[] a只占一个位置，因此总长度仅为b.length + 1。试试这个：

public <T> T[][] concatenate (T[] a, T[][] b) {
    T[][] c = (T[][]) Array.newInstance(a.getClass(), b.length + 1);
    c[0] = a;
    System.arraycopy(b, 0, c, 1, b.length);
    return c;
}

由于以上只能将1D阵列连接到2D阵列，而不是相反（因为您需要在表格下方添加＆＃39;总计＆＃39;行，更一般方法是编写一个通用＆＃34;连接2个具有相同维度的数组＆＃34;方法，以及另一个将元素包装到数组中的方法。

public <T> T[] wrap(T x) {
    T[] a = (T[]) Array.newInstance(x.getClass(), 1);
    a[0] = x;
    return a;
}

public <T> T[] concatenate (T[] a, T[] b) {
    T[] c = (T[]) Array.newInstance(a.getClass().getComponentType(), a.length + b.length);
    System.arraycopy(a, 0, c, 0, a.length);
    System.arraycopy(b, 0, c, a.length, b.length);
    return c;
}

示例：

String[] headercol = {"Type","Asc","Ref","Commandes","Prix unitaire","Prix total"};
String[][] content = {{"A","B","C","D","E","F","G","H"}, {"1","2","3","4","5","6","7","8"}};
String[] footer = {"a","b","c","d","e","f","g","h"};

String[][] global = (String[][]) concatenate (wrap(headercol),content);
global = (String[][]) concatenate (global, wrap(footer));

for (String[] row : global) {
    System.out.println(Arrays.toString(row));
}

输出：

[Type, Asc, Ref, Commandes, Prix unitaire, Prix total]
[A, B, C, D, E, F, G, H]
[1, 2, 3, 4, 5, 6, 7, 8]
[a, b, c, d, e, f, g, h]

Java Array连接

2 个答案: