Converting an array list to a single string

Question

I am working on a section of code for an assignment I am doing atm, and I am completely stuck with 1 little bit.

I need to convert the contents of an array list into a string, or the form of a string, which will be able to be imput into toString() in order for it to be printed to the screen.

public String toString(){
    String full;
    full = (this.name + this.address + "\n" + "Student Number = " + this.studentId);
    for (int i = 0; i < cs.size(); i++) {
        full.append(cs[i]);
    return full;

The piece of above code is where i attempt to combine 3 varaibles and the contents of an array list into a single string with formatting.

Unfortunatly it creates an error "The type of the expression must be an array type but it resolved to ArrayList"

Thanks for any help.

Jake

You need to use StringBuilder rather than String to build a String. — Peter Lawrey
– Peter Lawrey, Commented Sep 11, 2012 at 14:21
I recommend to use a StringBuilder instead of + for a String. — user647772
– user647772, Commented Sep 11, 2012 at 14:22

kosa · Accepted Answer · 2012-09-11 14:30:25Z

5

cs is array list, so you have to do get operation, not [] (which is for array access)

It should be like:

full.append(cs.get(i));

Not

full.append(cs[i]);

EDIT: As assylis said, full should be StringBuilder not just String, because String doesn't support append() method.

StringBuilder full = new StringBuilder();

edited Sep 11, 2012 at 14:30

answered Sep 11, 2012 at 14:21

kosa

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2 Comments

kosa Over a year ago

@assylias: Yes, edited my answer. I was concentrating more on error than other parts.

Jake Thomas Over a year ago

It worked with only a slight bit of modification, thanks alot for your help.

Brian Agnew · Accepted Answer · 2012-09-11 14:26:12Z

2

Apache Commons StringUtils has different varieties of join() methods that mean you don't have to write this yourself. You can specify the separator and even the prefix/suffix.

I would recommend you look at Apache Commons, not just for this but for lots of other useful stuff.

answered Sep 11, 2012 at 14:26

Brian Agnew

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Comments

asteri · Accepted Answer · 2012-09-11 14:28:24Z

2

You are attempting to access an ArrayList as though it is a primitive array (using the square brackets around the index). Try using the get(int index) method instead.

i.e.,

cs.get(i);

edited Sep 11, 2012 at 14:28

answered Sep 11, 2012 at 14:22

asteri

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Comments

Tudor · Accepted Answer · 2012-09-11 14:23:52Z

0

You cannot index an ArrayList like an array, you need the get(index) method. Even better, use the enhanced for loop, since it's not recommended to index over a list, as the implementation may change to LinkedList.

I also suggest using a StringBuilder for efficiency:

public String toString() {
    StringBuilder full = new StringBuilder();
    full.append(this.name);
    full.append(this.address);
    full.append("\n");
    full.append("Student Number = ");
    full.append(this.studentId);
    for (String s: cs)
        full.append(s);
    return full.toString();
}

answered Sep 11, 2012 at 14:23

Tudor

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Comments

Vijay · Accepted Answer · 2012-09-11 14:32:32Z

0

Just use "cs.get(i)" in place of "cs[i]". as cs is an ArrayList not an Array.

and also use full = full + cs.get(i); and not full.append(cs.get(i));

as String type dont have a append method.

answered Sep 11, 2012 at 14:32

Vijay

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Comments

John B · Accepted Answer · 2012-09-11 14:49:38Z

0

Just a note, since you don't put any spacers between each element of the ArrayList it might be unreadable. Consider using Guava's Joiner class.

So instead of

 for (...)
   s.append(y);

if would be

   a.append(Joiner.on(" ").join(yourList));

The Joiner is also more efficient than the for loop since it uses a StringBuilder internally.

answered Sep 11, 2012 at 14:49

John B

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