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);
Leave a Reply
Clear and simple examples.
Keep it up!
Hi:
I keep learning a lot from your examples.. they are simple and to the point..thank you and 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));
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!