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.
Great examples. Thanks.
look like js :V
Clear and simple examples.
Keep it up!
Good page. Clear and simple examples. Thanks!
simple examples
Is it possible to describe a forEach without using println??
Making a more explainful example.
Your examples are clean and simple, easy to understand the core point. Thanks alot, Keep it up.
Hi Mkyong,
I really inspired by your way of explanation, very simple to understand.
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.
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.
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 .
Thank you for the simple snippets, to the explanations. Really helpful !!!
Very correct
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.
very good explanation of java 8
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
Hi mkyong.??
Can i have your email??
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
You ara wonderfull . You are lord .
Helal olsun krals?n
Thank you
Allah raz? olsun ????