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collections

How-to articles, tricks, and solutions about COLLECTIONS

Convert JSON to Map

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

json java parsing collections

Converting 'ArrayList<String> to 'String[]' 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:

java string arrays collections arraylist

Easiest way to convert a List to a Set in Java

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.

java collections

get string value from HashMap depending on key name

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.

java collections hashmap

Getting an element from a Set

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.

java set collections equals

How can I convert List<Integer> to int[] in Java?

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

java arrays collections

How can I initialise a static Map?

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.

java collections initialization dictionary idioms

How can I sort a List alphabetically?

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

java list collections sorting alphabetical

How can I turn a List of Lists into a List in Java 8?

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

java collections java-8

How do I convert a Map to List in Java?

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

java list collections dictionary

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