Java - Array

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.

• 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};

• 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);
}

Arrays.asList

Java - Stream Processing

Arrays.asList(array).stream()

for

for (int i = 0; i < anArray.length; i++) {
 
	System.out.println(i+" : "+anArray[i]);
 
}

int size = array.length;

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);

String[] arr = {"1","2","3"};
String[] arrMinOne = new String[arr.length-1];
System.arraycopy(arr,0,arrMinOne,0,arr.length-1);

import java.util.Arrays;
Arrays.equals(firstArray, secondArray));

Class literal

type[].class

Example for a byte:

byte[].class

String[] arr = {"1","2",""};
arr = Arrays
	.stream(arr)
	.map(s -> {
		if (s.equals("")) {
			return null;
		} else {
			return s;
		}
	})
	.toArray(String[]::new);

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());

String[] args = Arrays.copyOfRange(args, 1, args.length);

String.join(" ",args)

• Arrays