Databases
StackOverflow2013
Postsdbo
POHow does one access an ArrayList of ArrayLists? (Generics?)
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POHow does one access an ArrayList of ArrayLists? (Generics?)
    primarykey
    data
    text
    <p>I'm trying to create a table class, who's rows and columns may expand or shrink, to store ints and strings as a first Java project. The data structure I'm trying to use to represent the table is an ArrayList of ArrayLists, where the initial array's elements all point to a new array list - so the initial array kind of serves as an entrance into rows. This would be a picture of how I have it in my mind, for reference: </p> <p><a href="https://i.stack.imgur.com/wiXUa.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/wiXUa.png" alt="enter image description here"></a></p> <p>The problem I'm having is accessing the inner ArrayLists. I've been reading a bit of documentation, and I can't seem to understand the big issue with why I'm not able to access the inner lists. Some code here: </p> <pre><code>import java.util.ArrayList; public class Table { private int length, width; private ArrayList newTable; public Table() { this.length = this.width = 0; } /** * Testing a few functions */ public static void main(String[] args) { // Just testing a few functions. Table list1 = new Table(); list1.createTable(4, 4); list1.displayRow(1); list1.displayColumn(1); System.out.println("displayColumn done!"); list1.displayEntireTable(); } public void createTable(int tableLength, int tableWidth) { length = tableLength; width = tableWidth; this.newTable = new ArrayList(); for (int i = 0; i &lt; tableWidth; i++) { this.newTable.add(new ArrayList(tableLength)); } } public void displayRow(int row) { System.out.println(this.newTable.get(row)); } /** * This function displays the column of the table. Still work which * needs to be done here. * @param column */ public void displayColumn(int column) { if (this.newTable.size() &gt;= column) { for (int i = 0; i &lt; this.newTable.size(); i++) { // This doesn't work. System.out.println(this.newTable.get(i).get(column)); } } } public void displayEntireTable() { for (int i = 0; i &lt; this.newTable.size(); i++) { System.out.println(this.newTable.get(i)); } } } </code></pre> <p>I'm suspicious that the problem may rely the lack of use in generics, which I'm not quite as familiar with yet as I would like to be. So my question to you, stackoverflow, is whether this data structure - an ArrayList of ArrayLists - is even possible, and if so, where lays my problem?</p>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USfalsarella
    1. USMiles Stevenson
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    3. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POHow does one access an ArrayList of ArrayLists? (Generics?)
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. POHow does one access an ArrayList of ArrayLists? (Generics?)
      1. This table or related slice is empty.
      1. VTApproveEditSuggestion
    1. COOf course, it is possible. Just use Generics: `List<List<String>>`
      singulars
      1. POHow does one access an ArrayList of ArrayLists? (Generics?)
      1. UShome
    2. CO@Home Generics is a compile time help for type safety. A List in List is certainly possible without generics.
      singulars
      1. POHow does one access an ArrayList of ArrayLists? (Generics?)
      1. USFarmor
    3. COThe compilation error in "the line that doesn't work" is due to the fact that your calling `List.get(index)` on an `Object` retrieved from `newTable`.
      singulars
      1. POHow does one access an ArrayList of ArrayLists? (Generics?)
      1. USblackcompe
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload