Java 8 forEach examples
In this article, we will show you how to loop a List and a Map with the new Java 8 forEach statement.
1. forEach and Map
1.1 Normal way to loop a Map.
Map<String, Integer> items = new HashMap<>();
items.put("A", 10);
items.put("B", 20);
items.put("C", 30);
items.put("D", 40);
items.put("E", 50);
items.put("F", 60);
for (Map.Entry<String, Integer> entry : items.entrySet()) {
System.out.println("Item : " + entry.getKey() + " Count : " + entry.getValue());
}
1.2 In Java 8, you can loop a Map with forEach + lambda expression.
Map<String, Integer> items = new HashMap<>();
items.put("A", 10);
items.put("B", 20);
items.put("C", 30);
items.put("D", 40);
items.put("E", 50);
items.put("F", 60);
items.forEach((k,v)->System.out.println("Item : " + k + " Count : " + v));
items.forEach((k,v)->{
System.out.println("Item : " + k + " Count : " + v);
if("E".equals(k)){
System.out.println("Hello E");
}
});
2. forEach and List
2.1 Normal for-loop to loop a List.
List<String> items = new ArrayList<>();
items.add("A");
items.add("B");
items.add("C");
items.add("D");
items.add("E");
for(String item : items){
System.out.println(item);
}
2.2 In Java 8, you can loop a List with forEach + lambda expression or method reference.
List<String> items = new ArrayList<>();
items.add("A");
items.add("B");
items.add("C");
items.add("D");
items.add("E");
//lambda
//Output : A,B,C,D,E
items.forEach(item->System.out.println(item));
//Output : C
items.forEach(item->{
if("C".equals(item)){
System.out.println(item);
}
});
//method reference
//Output : A,B,C,D,E
items.forEach(System.out::println);
//Stream and filter
//Output : B
items.stream()
.filter(s->s.contains("B"))
.forEach(System.out::println);
References
About the Author
Hi:
I keep learning a lot from your examples.. they are simple and to the point..thank you and keep it up.
Hi Mkyong,
I really inspired by your way of explanation, very simple to understand.
very good explanation of java 8
Great examples. Thanks.
look like js :V
It really helped me.. thank you so much
The only think I don’t like using forEach is when you want to call inside it a service that throws exceptions, because you must catch them inside forEach loop. It doesn’t happen with “for” sentence, as you can have the try outside it.
lambda expressions are so unreadable and finally bullshit
final lamda = bullshit;
depends, it can save you a lot of for loops or even nested for loops, and that makes the sourcecode a lot more readable, taking out boiler plate code
Thanks, I was iterating a forEeah loop and instead of sysout. I want to perform few operations but I was getting an error. Your post help me identify what should I do.
Thank you for the simple snippets, to the explanations. Really helpful !!!
Very correct
Clear and simple examples.
Keep it up!
When I do this, I am getting a null pointer exception when the value in the map is null (v is null). How can I avoid that?
items.forEach((k,v)->System.out.println(“Item : ” + k + ” Count : ” + v));
if (items != null) items.forEach((k,v)->System.out.println(“Item : ” + k + ” Count : ” + v));
Optional.ofNullable(items).orElse(Collections.emptyMap())
.forEach((k, v) -> System.out.println(“Item : ” + k + ” Count : ” + v));
thanks for clear examples.
In section 2.2, last part – “//Steam and filter” line must be “stream” :) you can remove this comment after fix.
Fixed, thanks.
Good page. Clear and simple examples. Thanks!
hello, thanks for this tutorial. In Java 8 possible to use ‘::’ ?
items.forEach(System.out::println);
I checked it. It is equals the– items.forEach(item->System.out.println(item)); –?
Because the parameter and the return type is the same?
Sorry for dump question .
can we insert the records in bulk. I don’t want to run the loop again and again. Though of having a batch.
Please suggest.
//I am looking for loop using streams as follows:
int inputArray[] = {4, 6, 5, -10, 8, 1, 2};
for (int i : inputArray)
{
for (int j = i+1; j {
IntStream.range(i+1,… ).forEach(j -> {// stuck here
});
});
thank you for this nice and post
Hi mkyong.??
Can i have your email??
You ara wonderfull . You are lord .
Helal olsun krals?n
Thank you
Allah raz? olsun ????