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Installing Collection

Lists

List is an ordered collection with access to elements by indices – integer numbers that reflect their position. Elements can occur more than once in a list. In other words: a list can contain any number of equal objects or occurrences of a single object. Two lists are considered equal if they have the same sizes and structurally equal elements at the same positions.

Lists are completely new implemented for version 4.0. The handling is much more oriented on a functional approach. Further more methods for associative arrays are moved to map.

Getting started

Output

You also create a list from an existing array

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As you may notice, this will reset the array keys

You can also create an empty List:

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Iterate over lists

Output:

or

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List operations

You may add the elements of another list to a list by using plus:

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The same operation is applicable with arrays, with the same result:

You can also subtract the elements of another list or any iterable using minus:

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To get the intersection of two lists (or an iterable), you can use the intersect method:

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To get a list containing distinct elements, use distinct:

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Map all elements of a list

If you need to modify all elements in a list, you can do it easily by using the map method:

There is also a mapNotNull method that eliminates null values from the result:

Filter elements in a list

The filter method returns a list containing only elements matching the given predicate.

Logical operations

With the methods any and all you can check whether all elements (all) or at least one element (any) match a predicate.

forEach method

With the forEach method you can apply a closure or lambda functions on each element.

output:

Sorting a list

Implement the Comparable interface

Create a comparator class

Sort your list

sort your list using a custom order

Maps

A Map stores key-value pairs; keys are unique, but different keys can be paired with equal values. The Map interface provides specific methods, such as access to value by key, searching keys and values, and so on.

Getting started

A Map is a collection of keys that are paired with values. Therefore, to create a Map you need pairs first:

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You can also create an empty Map:

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Access elements

you are also able to get all map entries as a list of pairs

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Manipulate a map

Map elements

The signature of given transform function for mapping must have either a Pair parameter or a key and a value parameter. The map function always returns a list of type ListInterface:

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You get the same result with a key-value signature:

Filter entries of a map

You may filter for elements by this way:

or by this way:

Combining Lists and Maps

There are a lot of opportunities to use lists and maps in real world scenarios with a lot of advantages e.g. less boilerplate code and better code readability.

The following json file represents a customer file that we want to use for processing.

customer.json

We would like to get a map that associates the customer id with respective objects of type Customer and we want to apply a filter so that we get only customers with lastname Doe.

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Another example: Assuming we have a customer service with a getCustomerById method. We have a list of IDs with which we want to request the service.

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Stack

A stack is a collection of elements, with two principal operations:

• push, which adds an element to the collection, and
• pop, which removes the most recently added element that was not yet removed.

An Stack is a LIFO data structure: last in, first out.

Examples

push, pop and peek

search

The search function returns the position where an element is on this stack. If the passed element occurs as an element in this stack, this method returns the distance from the top of the stack of the occurrence nearest the top of the stack; the topmost element on the stack is considered to be at distance 1. If the passed element does not occur in the stack, this method returns 0.

Queue

A queue is a collection in which the elements are kept in order. A queue has two principle operations:

• enqueue
• dequeue

Examples

Contribution

Fork this Repo and feel free to contribute your ideas using pull requests.