Printing an arraylist with an enhanced foor loop - error: cannot find symbol and variable already defined in method

Question

I am new to java and am trying to write a method that will print out an ArrayList using an enhanced for loop. Whenever I compile, the fore loop gives me the following errors:

error: cannot find symbol

error: variable list2 is already defined in method printLists(ArrayList,ArrayList) for(String list2: list)

public static void printLists(ArrayList <String> list1, ArrayList <String> list2 )
{
    System.out.println("list1.txt contains:");
    for(String list1: list)
        System.out.println(list1+ " ");

    System.out.println("list2.txt contains:");
    for(String list2: list)
        System.out.println(list2+ " ");
}

Can someone please explain to me what these errors mean?

Gilad Green · Accepted Answer · 2017-06-04T05:26:45.680

4

The use of the for-each loop is incorrect:

for(String list1: list)

Two problems with this line:

As error says you are trying to define a new variable names list1 of type String but you already have such a variable name in the scope.
There is nothing defined as list. Basically the syntax is that: for(#item : #collection)

You are looking for something like

for(String item : list1)

Read more on How does the Java 'for each' loop work?

A nicer way to print list will be to use String.join as seen here

System.out.println(String.join(" ", list1));

edited Jun 04 '17 at 05:26

answered Jun 04 '17 at 05:14

Gilad Green

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Thanks for the answer and clarification! I'll check out the link and accept it once the time lock is gone :). – starlight Jun 04 '17 at 05:17
@starlight - you are welcome :) Let me know how it goes :) – Gilad Green Jun 04 '17 at 05:18

Elliott Frisch · Answer 2 · 2017-06-04T05:25:05.577

You've swapped list and list1 (and list2) in your for-each loops. However, I would first suggest you program to the List interface. And assuming you are using Java 8+, I would prefer to stream() the contents and join them with a Collector. Like,

public static void printLists(List<String> list1, List<String> list2) {
    System.out.printf("list1.txt contains: %s%n", list1.stream()
            .collect(Collectors.joining(" ")));
    System.out.printf("list2.txt contains: %s%n", list2.stream()
            .collect(Collectors.joining(" ")));
}

or possibly make the arguments variadic and generic (so it can take any number of Lists of any type) like

@SafeVarargs
public static <T> void printLists(List<T>... lists) {
    for (int i = 0; i < lists.length; i++) {
        System.out.printf("list%d.txt contains: %s%n", i + 1,
                lists[i].stream().map(Object::toString).collect(
                        Collectors.joining(" ")));
    }
}

Printing an arraylist with an enhanced foor loop - error: cannot find symbol and variable already defined in method

2 Answers2