Various Approaches to Traverse the Collection.

We can traverse the List, Queue, Set, and Map interface in various approaches. Like - Loop, Iterator, Lamda Expressions, and Java Streams. Below are the different traverse methods for such interfaces.

Traverse Approaches are - 

1. For Loop
2. Enhanced For Loop
3. Iterator
4. Stream API
5. Lamda Expression (forEach)

List, Queue, and Set use the same syntax. Therefore, just ArrayList is shown below.

        List<String> list = new ArrayList<>();

        list.add("A");

        list.add("B");

        list.add("C");

1. For Loop

for (int i = 0; i < list.size(); i++) {

    System.out.println(list.get(i));

}

2. Enhanced For Loop

for (String item : list) {

    System.out.println(item);

}

3. Iterator

Iterator<String> iterator = list.iterator();

while (iterator.hasNext()) {

    System.out.println(iterator.next());

}

 4. Stream API

list.stream().forEach(System.out::println);

5. Stream using Lamda Expression

list.stream().forEach(item -> {

    String result = item.toLowerCase();

    System.out.println("Processed: " + result);

});

    Executed code

 

Map Interface: 

        Map<String, Integer> map = new HashMap<>();

        map.put("A", 1);

        map.put("B", 2);

        map.put("C", 3);

1. Enhance for loop (entry set)

for (Map.Entry<String, Integer> entry : map.entrySet()) {

    System.out.println(entry.getKey() + " = " + entry.getValue());

}

2. Enhance for loop (key set)

for (String key : map.keySet()) {

    System.out.println(key + " = " + map.get(key));

}

3. Enhance for loop (values)

for (Integer value : map.values()) {

    System.out.println(value);

}

4. Iterator

Iterator<Map.Entry<String, Integer>> iterator = map.entrySet().iterator();

while (iterator.hasNext()) {

    Map.Entry<String, Integer> entry = iterator.next();

    System.out.println(entry.getKey() + " = " + entry.getValue());

}

5. Stream API

map.entrySet().stream().forEach(entry -> 

    System.out.println(entry.getKey() + " = " + entry.getValue()));

6. Using Lamda Expression

map.forEach((key, value) -> System.out.println(key + " = " + value));

Executed code