Java adding data to a nested array

Question

How can I use the same arraylist row to add values into the nested array tableValues since the clear command removes the data in row.

Thanks

    ArrayList<ArrayList<String>> tableValues = new ArrayList<ArrayList<String>>();
    ArrayList<String> row = new ArrayList<String>();

    row.add("a");
    row.add("b");
    row.add("c");
    tableValues.add(row);
    row.clear();

    row.add("d");
    row.add("e");
    row.add("f");
    tableValues.add(row);
    row.clear();

    row.add("g");
    row.add("h");
    row.add("i");
    tableValues.add(row);
    row.clear();

    System.out.println(tableValues);

Jon Skeet · Accepted Answer · 2011-12-15 07:15:39Z

3

I'm sure you really want to add three different ArrayLists, so change each row.clear() to:

row = new ArrayList<String>();

Why would you want to "use the same arraylist row to add values"? I can't see why you'd want your top-level ArrayList to basically contain the same reference three times. Why would you not want them to be references to independent lists?

answered Dec 15, 2011 at 7:15

Jon Skeet

1.5m893 gold badges9.3k silver badges9.3k bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Ricco Over a year ago

What I meant was I didn't want to have row1, row2 row3 etc since I don't know how many rows there are, so that would cause a problem :)

Jon Skeet Over a year ago

@Ricco: Right - it's worth differentiating between objects and variables. You're now using one variable, but it will have three different values over its lifetime. (I'd be tempted to refactor the "add a row" part into a separate method, but that's a slightly different topic where I'd need more context.)

Alpedar · Accepted Answer · 2011-12-15 08:12:00Z

0

Use something like

ArrayList<String> row;

row = new ArrayList<String>();
// fill row
tableValues.add(row);

row = new ArrayList<String>();
// fill row
tableValues.add(row);

This way you don't need in your code variable for each row. or put it in cycle

while(codnition) { // or for or do {} while(condition);
   List<String> row = new  ArrayList<String>();
   // fill row
   table.add(row);
}

This way there single name for currently added row, but scope of this variable is only inside given iteration of cycle.

answered Dec 15, 2011 at 8:12

Alpedar

1,3541 gold badge8 silver badges14 bronze badges

Collectives™ on Stack Overflow

Java adding data to a nested array

2 Answers 2

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related