How to add info from different locations in arrayList to a single string

Question

I am trying to create a method which returns a single String (not String array) containing information for all objects in my array list. I know that strings are immutable so I am really struggling with how to add information from each object.

This is my method where I am trying to return a single string:

public String infoForEachItem ()
{
    String info;
    for (int y =0; y < items.size(); y++)
    {
        info = "ID: " + items.get(y).getId() + "\n" +
                "Name : " + items.get(y).getName() + "\n" +
                "Cost: " + items.get(y).getCost() + "\n";
        return info;
    }
}

As you can see, I want to create a string containing the Id, name, and cost of EACH item as a single string. It won't let me return within a for loop. Is there anyway to append something to the end of String?

Use a `StringBuilder` instead, use its `append` method to add to it and then *after* the loop return its content using its `toString` method. — Federico klez Culloca, Apr 26 '22 at 18:44
We can use string concatenation, e.g `info += ...` (but `info` must be initialized beforehand, e.g. with `String info = "";`). We can also use a [`StringBuilder`](https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/StringBuilder.html). --- A remark: we most probably do not want the `return` where it is right now. — Turing85, Apr 26 '22 at 18:44
Thank you so much for the help! I totally forgot about StringBuilder — MKK, Apr 26 '22 at 18:58
See [my Answer](https://stackoverflow.com/a/31169001/642706) to a similar question, to see a diagram I made as an overview of the various textual data types in Java: `String`, `StringBuilder`, `StringBuffer`, `CharSequence`, and more. — Basil Bourque, Apr 26 '22 at 20:10

score 2 · Answer 1 · edited Apr 26 '22 at 20:08

`StringBuilder`

Use StringBuilder to build up text by appending multiple times.

Here is some code expanding on comment by Federico klez Culloca:

public String infoForEachItem ()
{
    StringBuilder result = new StringBuilder();
    for (Item item : items) {
        result.append("ID: ").append(item.getId()).append('\n');
        result.append("Name: ").append(item.getName()).append('\n');
        result.append("Cost: ").append(item.getCost()).append("\n\n");
    }
    return result.toString();
}

You can chain the calls to .append as you think it is suitable, and there are overloads of the method for many parameter types.

How to add info from different locations in arrayList to a single string

1 Answers1

StringBuilder

`StringBuilder`