Java - Array
Table of Contents
1 - About
Collection - Array in Java.
Arrays implement most of the List operations, but not remove and add. They are “fixed-size” Lists.
An array is a container object that holds :
- a fixed number of values
- of a single type.
The length of an array is established when the array is created. After creation, its length is fixed.
In Java, arrays cannot be resized dynamically. Another approach is to use a list.
2 - Articles Related
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3 - Management
3.1 - Initialization
- Declaration
// declares an array of // - integers int[] anArray; // - string String[] anArray // ...
- Memory Allocation
// allocates memory for 3 integers with the index (0,1,2) anArray = new int[3]; // allocates memory for 3 strings anArray = new String[3];
- Unit Initialization
// initialize first element anArray[0] = "Nic"; // initialize second element anArray[1] = "o"; anArray[2] = "Nic"; anArray[3] = "Nicooooo"; // and so forth
- Array Initialization
int[] anArray= {1,2,3,4,5,6,7,8,9,10}; anArray= newInteger[]{1,2,3,4};
3.1.1 - List
- for arrays of reference types
Foo[] array = new Foo[list.size()]; list.toArray(array); // fill the array
- for arrays of primitive types
int[] array = new int[list.size()]; for(int i = 0; i < list.size(); i++) { array[i] = list.get(i); }
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3.2 - Conversion
3.2.1 - ToList
Arrays.asList
3.2.2 - ToStream
Arrays.asList(array).stream()
3.3 - Loop
3.3.1 - For
3.4 - Size
int size = array.length;
3.5 - Copy
char[] copyTo = java.util.Arrays.copyOfRange(copyFrom, 2, 9); char[] copyTo = java.util.Arrays.copyOf(copyFrom, copyFrom.length) System.arraycopy(copyFrom, 2, copyTo, 0, 7);
3.6 - Remove the last one
String[] arr = {"1","2","3"}; String[] arrMinOne = new String[arr.length-1]; System.arraycopy(arr,0,arrMinOne,0,arr.length-1);
3.7 - Equality
import java.util.Arrays; Arrays.equals(firstArray, secondArray));
3.8 - Class
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3.9 - Functional Programm
3.9.1 - Transformation
String[] arr = {"1","2",""}; arr = Arrays .stream(arr) .map(s -> { if (s.equals("")) { return null; } else { return s; } }) .toArray(String[]::new);
3.9.2 - Select by index
Example: select the even elements
List<String> evenElement = IntStream .range(0, elements.length) .filter(i -> i % 2 == 0) .mapToObj(i -> elements[i]) .collect(Collectors.toList());
3.10 - Slice
3.11 - Join
String.join(" ",args)