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Problem with lambda java8 and foreach expression

I have a list below

List<String> fruits = new ArrayList<>();
fruits.add("apple");
fruits.add("mango");
fruits.add("grapes");
System.out.println(fruits.toString());

I am using a lambda expression to print a list like

fruits.forEach(item->System.out.println(item));

and its working fine, my requirement is: I need to iterate over the list and concatenate the elements into a string

String stringFruits = "";
fruits.forEach(item->stringFruits = stringFruits+item);

this gives a compile-time error that the values ​​of the variables used in the lambda must be definitively final , is there a way to do this in java 8?

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4 answers


You don't need to do it manually. If your source is List

, you can simply use

String stringFruits = String.join(", ", fruits);
System.out.println(stringFruits);


The first argument String.join(…)

is a separator.

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You need join

through delimiter

. In this case, the separator will be ,

; but you can choose any you want.



 String result = fruits.stream().collect(Collectors.joining(","));
 System.out.println(result);
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Java8 introduces StringJoiner , which does what you want (this is another alternative to the default comment)

StringJoiner sj = new StringJoiner("-,-");
fruits.forEach(item -> sj.add(item));

here doc

edit:

for posterity, you can also do:

String result = fruits.stream().collect(Collectors.joining(","));
System.out.println(result);

or

String stringFruits = String.join(", ", fruits);
System.out.println(stringFruits);

credits and thanks to @Holger

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Or a pre-Java8 solution:

String combined = "";
for (String s : fruits) {
   combined += s;
}

... and one with a delimiter:

String combined = "";
for (String s : fruits) {
   combined = combined + ", " + s;
}
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