How-to articles, tricks, and solutions about COLLECTIONS

You can use the Gson library to convert a JSON string to a Map in Java.

You can use the toArray() method of the ArrayList class to convert an ArrayList of strings to a string array. Here's an example:

To convert a List to a Set in Java, you can use the new HashSet<>(list) constructor to create a new HashSet and initialize it with the elements of the List.

To get the string value from a HashMap depending on the key name in Java, you can use the get() method of the Map interface.

A Set is a collection of elements in which each element can only occur once. A Set does not have a specific order and does not provide a way to access its elements by their position.

You can use the toArray() method of the List interface to convert a List<Integer> to an int[] in Java.

To initialize a static Map in Java, you can use the Map interface's of method, which was added in Java 9. The of method creates an immutable Map with a fixed set of key-value pairs.

To sort a List alphabetically in Java, you can use the Collections.sort method and pass in your List as an argument.

You can use the flatMap method from the Stream API to turn a List&lt;List&lt;T&gt;&gt; (a list of lists) into a List&lt;T&gt; in Java 8. Here's an example of how you can do this:

You can use the entrySet() method of the Map interface to get a Set view of the mappings contained in the map, and then create a List from this set using the new

There are several ways to iterate over the entries in a Map in Java. Here are some options:

To remove repeated elements from an ArrayList in Java, you can use the removeAll method and pass it a Collection containing the elements to be removed.

To clone an ArrayList and also clone its contents, you can use the clone method of the ArrayList class, which creates a shallow copy of the list.

In Java, you can convert a Collection (such as Set, Queue, etc.) to a List using the following methods:

To convert an array to a Set in Java, you can use the Arrays.asList() method to create a List from the array, and then use the List.toSet() method to create a Set from the List.

To convert a comma-separated String to a List in Java, you can use the String.split() method to split the string into an array of substrings, and then use the Arrays.asList() method to create a list from that array.

To convert an int[] array into a List<Integer> in Java, you can use the Arrays.stream() method to create a stream of the array, and then use the mapToObj() method to map each element of the stream to an Integer object.

To count the number of occurrences of an element in a List in Java, you can use the Collections.frequency(Collection, Object) method, which returns the number of times the specified element appears in the collection.

To directly initialize a HashMap in Java, you can use the put() method to add elements to the map.

To filter a Java collection based on a predicate, you can use the removeIf method of the Collection interface. This method removes all elements from the collection that match the specified predicate.

To get the first element of a List or Set in Java, you can use the following methods:

You can initialize an ArrayList in one line in Java using the following syntax:

To initialize the values of a HashSet when constructing the set, you can use one of the HashSet constructors that takes a Collection as an argument.

In Java, you can create a new list using the java.util.ArrayList class or the java.util.LinkedList class.

To sort a List or ArrayList in Java, you can use the sort method of the Collections class from the java.util package. The sort method takes a List and sorts it in ascending order according to the natural ordering of its elements.