1. Introduction
Java Map is a powerful tool that allows us to associate objects and values – each key being distinct from the others. But wait, there’s more! In this article, you’ll discover ways to iterate over Map entries in Java. Get ready for exciting new insights into content association with Java Maps!
2. ForEach on Map Entry
This example presents how you can iterate over map entities:
private static void iterateViaForLoop(Map<String, String> map) {
for (Map.Entry<String, String> e : map.entrySet()) {
String msg = String.format("%s %s", e.getKey(), e.getValue());
System.out.println(msg);
}
}
Each map entry is a single element with a key and value assigned. For loop allows iteration over elements sequentially. Ideal when you are looking for a specific element based on some condition.
3. Java 8 ForEach
Here we are using Java 8 for each approach to achieve precisely the same thing as above:
private static void iterateViaJava8ForEach(Map<String, String> map) {
map.forEach((key, value) ->
System.out.println(String.format("%s %s", key, value)));
}
A more elegant way to achieve iteration over elements is using Java 8 Lambdas. Java 8 functional-style programming reduces boilerplate code.
4. Iterator on Map Entry
private static void iterateUsingIterator(Map<String, String> map) {
Set<Map.Entry<String, String>> entrySet = map.entrySet();
Iterator<Map.Entry<String, String>> mapIterator = entrySet.iterator();
while (mapIterator.hasNext()) {
Map.Entry<String, String> e = mapIterator.next();
String msg = String.format("%s %s", e.getKey(), e.getValue());
System.out.println(msg);
}
}
We are creating an iterator for all the map entries in the above example. hasNext method returns true if the next element exists, so we can get that entry using next().
When using an iterator to iterate over elements, you can use the remove method to remove an element. So far, all the previous approaches would have thrown ConcurrentModificationException.
5. Java 8 Streams
Steams API is an iterator with sequential and parallel operations capabilities on collections that uses internal iteration (Java is in control of iteration implementation):
private static void iterateUsingJava8Streams(Map<String, String> map) {
map
.entrySet()
.stream()
.forEach(e -> {
String msg = String.format("%s %s", e.getKey(), e.getValue());
System.out.println(msg);
});
}
Steams API internally uses an iterator. Using streams is justified when you need to do some extra processing on the collection, like filtering or mapping. Here it would simply be pointless because we can apply for each without invoking stream operation as seen in the previous examples.
6. Summary
This short article analyzed ways to iterate over map entries in Java. When iterating over maps, two methods stand above the rest. Whether you’re on a mission for an item without intending any changes or needing some customizability with removal options – there’s something efficient for searching every entry in your map! Iterator & stream API make snagging those particular elements more effortless than ever.
Daniel Barczak
Daniel Barczak is a software developer with a solid 9-year track record in the industry. Outside the office, Daniel is passionate about home automation. He dedicates his free time to tinkering with the latest smart home technologies and engaging in DIY projects that enhance and automate the functionality of living spaces, reflecting his enthusiasm and passion for smart home solutions.
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