A Complete Java Array Tutorial

Java Array

An array is a collection of elements of the same data type, stored in a contiguous memory location. Arrays are used to store multiple values in a single variable, instead of declaring separate variables for each value.

Features of Array

1. In Java, all arrays are dynamically allocated.
2. Since arrays are objects in Java, we can find their length using member length. This is different from C/C++ where we find length using sizeof function.
3. A Java array variable can also be declared like other variables with [] after the data type.
4. The variables in the array are ordered and each has an index beginning from 0.
5. Java array can also be used as a static field, a local variable or a method parameter.
6. The size of an array must be specified by an int value and not long or short.
7. The direct superclass of an array type is Object.

Shortcomings of Java

1. Every array type implements the interfaces Cloneable and java.io.Serializable.
2. The size of an Array can not be increased or decreased dynamically.
3. Array Class doesn’t have an add or remove methods in Java
4. Arrays Suffer from the issue of memory wastage.
5. To delete an element in an array we need to traverse throughout the array so this will reduce performance.
6. Arrays in java only support primitive data types.

Types of Array

1. One-Dimensional Array

This is a type of array which is arranged in the form of rows only i.e. all the elements are stored can only be visualized in a linear format/ 1D figure

import java.util.Arrays;  
import static java.lang.System.out;  
public class Csharpcorner {  
 public static void main(String[] args) {  
  int demo[] = {  
   10,  
   20,  
   15,  
   22,  
   35  
  };  
  out.println("Integer Array as List: " +  
   Arrays.asList(demo));  
 }  
}  

In the above code, we are creating a 1D array named  demo.

2. Two-Dimensional Array

This is a type of array which is arranged in the form of rows and columns i.e. all the elements stored can be visualized as a Matrix or in 2D figure

import static java.lang.System.out;  
import java.util.Arrays;  
public class Csharpcorner {  
 public static void main(String[] args) {  
  int demo[][] = {  
   {  
    2,  
    7,  
    9  
   },  
   {  
    3,  
    6,  
    1  
   },  
   {  
    7,  
    4,  
    2  
   }  
  };  
  for (int i = 0; i < 3; i++) {  
   for (int j = 0; j < 3; j++)  
    out.print(demo[i][j] + " ");  
   out.println();  
  }  
 }  
}  

In the above code, we are creating a 2D array named demo.

3. Multi-Dimensional / N-Dimensional Array

This is a type of array which is arranged in the form of  (N-C) rows and C columns, where N is the dimension of array and C is the number of columns i.e all the elements stored can be visualized as (N-C) x C dimensional matrix or in an N-dimensional figure

import java.util.Arrays;  
import static java.lang.System.out;  
public class Csharpcorner {  
 public static void main(String[] args) {  
  int demo[][][] = {  
   {  
    {  
     1,  
     -2,  
     3  
    }, {  
     2,  
     3,  
     4  
    }  
   },  
   {  
    {  
     -4, -5, 6, 9  
    },  
    {  
     1  
    },  
    {  
     2,  
     3  
    }  
   }  
  };  
  for (int[][] array2D: demo) {  
   for (int[] array1D: array2D) {  
    for (int item: array1D) {  
     out.println(item);  
    }  
   }  
  }  
 }  
}  

In the above code, we are creating a 3D array named demo.

java.util.Arrays

array class is part of a java utility library, which comes pre-installed and pre-built as part of JDK (Java Development Environment).

A constructor can be used to create empty java arrays of various dimensions.

import java.util.Arrays;  
public class Csharpcorner {  
 public static void main(String[] args) {  
  int[] arr = new int[5];  
  int[][] arr = new int[5][5];  
  int[][][] arr = new int[5][5][5];  
 }  
}   

The above code demonstrates how we use a constructor to create 1D, 2D, and 3D Arrays

Array Methods

1. Arrays.asList()

Syntax

_static List asList(T… a) _

This method returns a fixed-size list backed by the specified Arrays.

import java.util.Arrays;  
import static java.lang.System.out;  
public class Csharpcorner {  
 public static void main(String[] args) {  
  int demo[] = {  
   10,  
   20,  
   15,  
   22,  
   35  
  };  
  out.println("Integer Array as List: " +  
   Arrays.asList(demo));  
 }  
}   

In the above code, we will be getting a list type of result that is java.util.Arrays will get converted to java.util.List

2. Arrays.binarySearch()

Syntax

1. static int binarySearch(elementToBeSearched)

These methods search for the specified element in the array with the help of the Binary Search algorithm.

2. static int binarySearch(T[] a, int fromIndex, int toIndex, T key, Comparator c)

This method searches a range of the specified array for the specified object using the binary search algorithm.

import java.util.Arrays;  
public class Csharpcorner {  
 public static void main(String[] args) {  
  int demo[] = {  
   10,  
   15,  
   20,  
   22,  
   35  
  };  
  int Key = 22;  
  int loc = Arrays.binarySearch(demo, Key)  
  int loc1 = Arrays.binarySearch(demo, 1, 3, Key)  
 }  
}   

In the above code, we are using the binary search algorithm to search for 22, and the location of the element will be stored in the variable “loc”. To demonstrate the use of the second version of binarySearch() we use variable “loc1”, which will perform the search between on elements of location 1 to location 3. i.e we will get the output of loc=3 and loc1=-4 (loc1=-4 because we have specified the range to be between 1 and 3, had it be 1 to 4 we would have got the answer to be loc1=3)

3. Arrays.compare()

Syntax

compare(array 1, array 2)

This method compares two arrays passed as parameters lexicographically.

import java.util.Arrays;  
public class Csharpcorner {  
 public static void main(String[] args) {  
  int demo[] = {  
   10,  
   20,  
   15,  
   22,  
   35  
  };  
  int demo1[] = {  
   10,  
   15,  
   22  
  };  
  int out = Arrays.compare(demo, demo1);  
 }  
}   

In the above code, we are comparing if some of the elements of Array demo1 exist in the Array _demo. S_ince every element of demo1 exists in demo, hence the output will be 1 i.e true.

4. Arrays.compareUnsighned()

Syntax

compareUnsigned(array 1, array 2)

This method compares two arrays lexicographically, numerically treating elements as unsigned.

import java.util.Arrays;  
public class Csharpcorner {  
 public static void main(String[] args) {  
  int demo[] = {  
   10,  
   20,  
   15,  
   22,  
   35  
  };  
  int demo1[] = {  
   -10,  
   -15,  
   22  
  };  
  int out = Arrays.compareUnsigned(demo, demo1);  
 }  
}   

Note: the above method may or may not run on systems, as some JDK versions support this method and some don’t

In the above code, we are comparing if some of the elements of Array demo1 exist in the Array _demo. S_ince every element of demo1 exists in the demo, hence the output will be 1 i.e true

5. Arrays.copyOf()

Syntax

copyOf(originalArray, newLength)

This method copies the specified array, truncating or padding with the default value (if necessary) so the copy has the specified length.

import java.util.Arrays;  
public class Csharpcorner {  
 public static void main(String[] args) {  
  int demo[] = {  
   10,  
   20,  
   15,  
   22,  
   35  
  };  
  int demo1[] = Arrays.copyOf(demo, 10);  
 }  
}   

In the above code, we will be increasing the size of new array to 10, since we are copying the elements of Array demo into Array demo1, and demo has only 5 elements, hence the value of next 5 elements will be zero, i.e _demo1 _ will be {10, 20, 15, 22, 35, 0, 0, 0, 0, 0}

6. Arrays.copyOfRange()

Syntax

copyOfRange(originalArray, fromIndex, endIndex)

This method copies the specified range of the specified array into new Arrays.

import java.util.Arrays;  
public class Csharpcorner {  
 public static void main(String[] args) {  
  int demo[] = {  
   10,  
   20,  
   15,  
   22,  
   35  
  };  
  int demo1[] = Arrays.copyOfRange(demo, 1, 3);  
 }  
}   

In the above code, we are creating a new Array demo1 which contains the array elements of location 1 to 3 from array demo.

7. Arrays.deepEquals()

Syntax

static boolean deepEquals(Object[] a1, Object[] a2)

This method returns true if the two specified arrays are deeply equal.

import java.util.Arrays;  
public class Csharpcorner {  
 public static void main(String[] args) {  
  int demo[] = {  
   10,  
   20,  
   15,  
   22,  
   35  
  };  
  int demo1[] = {  
   10,  
   15,  
   22  
  };  
  boolean ans = Arrays.deepEquals(demo, demo1);  
 }  
}   

In the above code, we are comparing if all the elements of Array demo1 exist in the Array _demo. S_ince every element of demo1 does not exist in the demo, hence the output will be 1 i.e false

8. Arrays.deepHashCode()

Syntax

static int deepHashCode(Object[] a)

This method returns a hash code based on the “deep contents” of the specified Arrays.

import java.util.Arrays;  
public class Csharpcorner {  
 public static void main(String[] args) {  
  int demo[][] = {  
   {  
    10,  
    20,  
    15,  
    22,  
    35  
   }  
  };  
  int ans = Arrays.deepHashCode(demo);  
 }  
}   

Note: the method will not work on a 1D array

In the above code, we will get a Hash Code based on the given array, hence the output will be 38475344

9. Arrays.deepToString()

Syntax

static String deepToString(Object[] a)

This method returns a string representation of the “deep contents” of the specified Arrays.

import java.util.Arrays;  
import static java.lang.System.out;  
public class Csharpcorner {  
 public static void main(String[] args) {  
  int demo[][] = {  
   {  
    10,  
    20,  
    15,  
    22,  
    35  
   }  
  };  
  String ans;  
  ans = Arrays.deepToString(demo);  
  out.print(ans);  
 }  
}   

In the above code, the method will return a String object of array_ demo._

10. Arrays.equals()

Syntax

equals(array1, array2)

This method checks if both the arrays are equal or not.

import java.util.Arrays;  
import static java.lang.System.out;  
public class Csharpcorner {  
 public static void main(String[] args) {  
  int demo[] = {  
   10,  
   20,  
   15,  
   22,  
   35  
  };  
  int demo1[] = {  
   10,  
   15,  
   22  
  };  
  boolean ans;  
  ans = Arrays.equals(demo, demo1);  
  out.print(ans);  
 }  
}   

In the above code, we check whether both size and elements match in both the demo and demo1 array. Hence, the output will be false

11. Arrays.fill()

Syntax

fill(originalArray, fillValue)

This method assigns this fillvalue to each index of these Arrays.

import static java.lang.System.out;  
import java.util.Arrays;  
public class Csharpcorner {  
 public static void main(String[] args) {  
  int demo[] = {  
   10,  
   20,  
   15,  
   22,  
   35  
  };  
  int intKey = 22;  
  Arrays.fill(demo, intKey);  
  out.print(Arrays.toString(demo));  
 }  
}   

In the above code, we will replace each element value with the fillValue i.e. 22

12. Arrays.hashCode()

Syntax

hashCode(originalArray)

This method returns an integer hashCode of this array instance.

import static java.lang.System.out;  
import java.util.Arrays;  
public class Csharpcorner {  
 public static void main(String[] args) {  
  int demo[][] = {  
   {  
    10,  
    20,  
    15,  
    22,  
    35  
   }  
  };  
  int ans = Arrays.hashCode(demo);  
  out.print(ans);  
 }  
}   

In the above code, we will be generating a hash code based on the given array. Here the output will be 366712673.

13. Arrays.mismatch()

Syntax

mismatch(array1, array2)

This method finds and returns the index of the first unmatched element between the two specified arrays

import java.util.Arrays;  
import static java.lang.System.out;  
public class Csharpcorner {  
 public static void main(String[] args) {  
  int demo[] = {  
   10,  
   20,  
   15,  
   22,  
   35  
  };  
  int demo1[] = {  
   10,  
   15,  
   22  
  };  
  int ans;  
  ans = Arrays.mismatch(demo, demo1);  
  out.print(ans);  
 }  
}   

Note: the above method may or may not run on systems, as some JDK versions support this method and some don’t.

In the above code, the output will be 1 as demo1[1] and demo[0] does not match.

14. Arrays.parallelSort()

Syntax

parallelSort(originalArray)

This method sorts the specified array using a parallel sort.

import java.util.Arrays;  
import static java.lang.System.out;  
public class Csharpcorner {  
 public static void main(String[] args) {  
  int demo[] = {  
   10,  
   20,  
   15,  
   22,  
   35  
  };  
  Arrays.parallelSort(demo);  
  out.print(Arrays.toString(demo));  
 }  
}   

In the above code, we will get an array demo sorted in ascending order_._

15. Arrays.sort()

Syntax

1. sort(original arrayoriginalArray)

This method sorts the complete array in ascending order.

2.  sort(originalArray, fromIndex, endIndex)

This method sorts the specified range of array in ascending order.

3. static void sort(T[] a, int fromIndex, int toIndex, Comparator c)

This method sorts the specified range of the specified array of objects according to the order induced by the specified comparator.

4. static void sort(T[] a, Comparator c)

This method sorts the specified array of objects according to the order induced by the specified comparator.

import java.util.Arrays;  
import static java.lang.System.out;  
public class Csharpcorner {  
 public static void main(String[] args) {  
  int demo[] = {  
   10,  
   20,  
   15,  
   22,  
   35  
  };  
  Arrays.sort(demo);  
  out.print(Arrays.toString(demo));  
  Arrays.sort(demo, 1, 3);  
  out.print(Arrays.toString(demo));  
 }  
}   

Note: thedifference between parallelSort() and sort() is that Parallel Sort uses Fork/Join framework introduced in Java 7 to assign the sorting tasks to multiple threads available in the thread pool.

In the above code, we will get an array demo sorted in ascending orderin both cases as in the second case we are sorting demo[1] to demo[3], which is the only part that is unsorted

16. Arrays.spliterator()

Syntax

1. spliterator(originalArray)

This method returns a Spliterator covering all of the specified Arrays.

2.  spliterator(originalArray, fromIndex, endIndex)

import java.util.Arrays;  
import java.util.Spliterator;  
import static java.lang.System.out;  
public class Csharpcorner {  
 public static void main(String[] args) {  
  int demo[] = {  
   10,  
   20,  
   15,  
   22,  
   35  
  };  
  Spliterator.OfInt demo1 = Arrays.spliterator(demo);  
  out.print(demo1);  
  Spliterator.OfInt demo2 = Arrays.spliterator(demo, 1, 3);  
  out.print(demo2);  
 }  
}   

This method returns a Spliterator of the type of the array covering the specified range of the specified Arrays.

In the above code, we are first converting the whole of the array demo to spliterator and then converting a part of array demo to spliterator.

17. Arrays.stream()

Syntax

stream(originalArray)

This method returns a sequential stream with the specified array as its source.

import java.util.Arrays;  
import static java.lang.System.out;  
public class Csharpcorner {  
 public static void main(String[] args) {  
  int demo[] = {  
   10,  
   20,  
   15,  
   22,  
   35  
  };  
  out.println("Integer Array: " +  
   Arrays.stream(demo));  
 }  
}   

In the above, we are trying to get a sequential stream with the specified array demo as the source i.e. Integer Array: java.util.stream.IntPipeline$Head@6d06d69c as the output

18. Arrays.toString()

Syntax

toString(originalArray)

This method returns a string representation of the contents of these Arrays. The string representation consists of a list of the array’s elements, enclosed in square brackets (“[]”). Adjacent elements are separated by the characters a comma followed by a space. Elements are converted to strings as by String.valueOf() function.

import static java.lang.System.out;  
import java.util.Arrays;  
public class Csharpcorner {  
 public static void main(String[] args) {  
  int demo[] = {  
   10,  
   20,  
   15,  
   22,  
   35  
  };  
  out.println("Integer Array: " +  
   Arrays.toString(demo));  
 }  
}   

In the above, we are converting java.util.Arrays to java.lang.String, i.e. converting to String from Array

Conclusion

In the article, we learned about Array, features of Array, Shortcomings of Array, Types of Arrays, Array Methods and how to use the Array Class and methods using Java.

Thank you for reading!

#java #array #tutorial #programming

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Buddha Community

How to Create Arrays in Python

In this tutorial, you'll know the basics of how to create arrays in Python using the array module. Learn how to use Python arrays. You'll see how to define them and the different methods commonly used for performing operations on them.

This tutorialvideo on 'Arrays in Python' will help you establish a strong hold on all the fundamentals in python programming language. Below are the topics covered in this video:  
1:15 What is an array?
2:53 Is python list same as an array?
3:48  How to create arrays in python?
7:19 Accessing array elements
9:59 Basic array operations
        - 10:33  Finding the length of an array
        - 11:44  Adding Elements
        - 15:06  Removing elements
        - 18:32  Array concatenation
       - 20:59  Slicing
       - 23:26  Looping  

---

Python Array Tutorial – Define, Index, Methods

In this article, you'll learn how to use Python arrays. You'll see how to define them and the different methods commonly used for performing operations on them.

The artcile covers arrays that you create by importing the array module. We won't cover NumPy arrays here.

Table of Contents

1. Introduction to Arrays
   1. The differences between Lists and Arrays
   2. When to use arrays
2. How to use arrays
   1. Define arrays
   2. Find the length of arrays
   3. Array indexing
   4. Search through arrays
   5. Loop through arrays
   6. Slice an array
3. Array methods for performing operations
   1. Change an existing value
   2. Add a new value
   3. Remove a value
4. Conclusion

Let's get started!

What are Python Arrays?

Arrays are a fundamental data structure, and an important part of most programming languages. In Python, they are containers which are able to store more than one item at the same time.

Specifically, they are an ordered collection of elements with every value being of the same data type. That is the most important thing to remember about Python arrays - the fact that they can only hold a sequence of multiple items that are of the same type.

What's the Difference between Python Lists and Python Arrays?

Lists are one of the most common data structures in Python, and a core part of the language.

Lists and arrays behave similarly.

Just like arrays, lists are an ordered sequence of elements.

They are also mutable and not fixed in size, which means they can grow and shrink throughout the life of the program. Items can be added and removed, making them very flexible to work with.

However, lists and arrays are not the same thing.

Lists store items that are of various data types. This means that a list can contain integers, floating point numbers, strings, or any other Python data type, at the same time. That is not the case with arrays.

As mentioned in the section above, arrays store only items that are of the same single data type. There are arrays that contain only integers, or only floating point numbers, or only any other Python data type you want to use.

When to Use Python Arrays

Lists are built into the Python programming language, whereas arrays aren't. Arrays are not a built-in data structure, and therefore need to be imported via the array module in order to be used.

Arrays of the array module are a thin wrapper over C arrays, and are useful when you want to work with homogeneous data.

They are also more compact and take up less memory and space which makes them more size efficient compared to lists.

If you want to perform mathematical calculations, then you should use NumPy arrays by importing the NumPy package. Besides that, you should just use Python arrays when you really need to, as lists work in a similar way and are more flexible to work with.

How to Use Arrays in Python

In order to create Python arrays, you'll first have to import the array module which contains all the necassary functions.

There are three ways you can import the array module:

• By using import array at the top of the file. This includes the module array. You would then go on to create an array using array.array().

import array

#how you would create an array
array.array()

• Instead of having to type array.array() all the time, you could use import array as arr at the top of the file, instead of import array alone. You would then create an array by typing arr.array(). The arr acts as an alias name, with the array constructor then immediately following it.

import array as arr

#how you would create an array
arr.array()

• Lastly, you could also use from array import *, with * importing all the functionalities available. You would then create an array by writing the array() constructor alone.

from array import *

#how you would create an array
array()

How to Define Arrays in Python

Once you've imported the array module, you can then go on to define a Python array.

The general syntax for creating an array looks like this:

variable_name = array(typecode,[elements])

Let's break it down:

• variable_name would be the name of the array.
• The typecode specifies what kind of elements would be stored in the array. Whether it would be an array of integers, an array of floats or an array of any other Python data type. Remember that all elements should be of the same data type.
• Inside square brackets you mention the elements that would be stored in the array, with each element being separated by a comma. You can also create an empty array by just writing variable_name = array(typecode) alone, without any elements.

Below is a typecode table, with the different typecodes that can be used with the different data types when defining Python arrays:

TYPECODE	C TYPE	PYTHON TYPE	SIZE
'b'	signed char	int	1
'B'	unsigned char	int	1
'u'	wchar_t	Unicode character	2
'h'	signed short	int	2
'H'	unsigned short	int	2
'i'	signed int	int	2
'I'	unsigned int	int	2
'l'	signed long	int	4
'L'	unsigned long	int	4
'q'	signed long long	int	8
'Q'	unsigned long long	int	8
'f'	float	float	4
'd'	double	float	8

Tying everything together, here is an example of how you would define an array in Python:

import array as arr 

numbers = arr.array('i',[10,20,30])


print(numbers)

#output

#array('i', [10, 20, 30])

Let's break it down:

• First we included the array module, in this case with import array as arr .
• Then, we created a numbers array.
• We used arr.array() because of import array as arr .
• Inside the array() constructor, we first included i, for signed integer. Signed integer means that the array can include positive and negative values. Unsigned integer, with H for example, would mean that no negative values are allowed.
• Lastly, we included the values to be stored in the array in square brackets.

Keep in mind that if you tried to include values that were not of i typecode, meaning they were not integer values, you would get an error:

import array as arr 

numbers = arr.array('i',[10.0,20,30])


print(numbers)

#output

#Traceback (most recent call last):
# File "/Users/dionysialemonaki/python_articles/demo.py", line 14, in <module>
#   numbers = arr.array('i',[10.0,20,30])
#TypeError: 'float' object cannot be interpreted as an integer

In the example above, I tried to include a floating point number in the array. I got an error because this is meant to be an integer array only.

Another way to create an array is the following:

from array import *

#an array of floating point values
numbers = array('d',[10.0,20.0,30.0])

print(numbers)

#output

#array('d', [10.0, 20.0, 30.0])

The example above imported the array module via from array import * and created an array numbers of float data type. This means that it holds only floating point numbers, which is specified with the 'd' typecode.

How to Find the Length of an Array in Python

To find out the exact number of elements contained in an array, use the built-in len() method.

It will return the integer number that is equal to the total number of elements in the array you specify.

import array as arr 

numbers = arr.array('i',[10,20,30])


print(len(numbers))

#output
# 3

In the example above, the array contained three elements – 10, 20, 30 – so the length of numbers is 3.

Array Indexing and How to Access Individual Items in an Array in Python

Each item in an array has a specific address. Individual items are accessed by referencing their index number.

Indexing in Python, and in all programming languages and computing in general, starts at 0. It is important to remember that counting starts at 0 and not at 1.

To access an element, you first write the name of the array followed by square brackets. Inside the square brackets you include the item's index number.

The general syntax would look something like this:

array_name[index_value_of_item]

Here is how you would access each individual element in an array:

import array as arr 

numbers = arr.array('i',[10,20,30])

print(numbers[0]) # gets the 1st element
print(numbers[1]) # gets the 2nd element
print(numbers[2]) # gets the 3rd element

#output

#10
#20
#30

Remember that the index value of the last element of an array is always one less than the length of the array. Where n is the length of the array, n - 1 will be the index value of the last item.

Note that you can also access each individual element using negative indexing.

With negative indexing, the last element would have an index of -1, the second to last element would have an index of -2, and so on.

Here is how you would get each item in an array using that method:

import array as arr 

numbers = arr.array('i',[10,20,30])

print(numbers[-1]) #gets last item
print(numbers[-2]) #gets second to last item
print(numbers[-3]) #gets first item
 
#output

#30
#20
#10

How to Search Through an Array in Python

You can find out an element's index number by using the index() method.

You pass the value of the element being searched as the argument to the method, and the element's index number is returned.

import array as arr 

numbers = arr.array('i',[10,20,30])

#search for the index of the value 10
print(numbers.index(10))

#output

#0

If there is more than one element with the same value, the index of the first instance of the value will be returned:

import array as arr 


numbers = arr.array('i',[10,20,30,10,20,30])

#search for the index of the value 10
#will return the index number of the first instance of the value 10
print(numbers.index(10))

#output

#0

How to Loop through an Array in Python

You've seen how to access each individual element in an array and print it out on its own.

You've also seen how to print the array, using the print() method. That method gives the following result:

import array as arr 

numbers = arr.array('i',[10,20,30])

print(numbers)

#output

#array('i', [10, 20, 30])

What if you want to print each value one by one?

This is where a loop comes in handy. You can loop through the array and print out each value, one-by-one, with each loop iteration.

For this you can use a simple for loop:

import array as arr 

numbers = arr.array('i',[10,20,30])

for number in numbers:
    print(number)
    
#output
#10
#20
#30

You could also use the range() function, and pass the len() method as its parameter. This would give the same result as above:

import array as arr  

values = arr.array('i',[10,20,30])

#prints each individual value in the array
for value in range(len(values)):
    print(values[value])

#output

#10
#20
#30

How to Slice an Array in Python

To access a specific range of values inside the array, use the slicing operator, which is a colon :.

When using the slicing operator and you only include one value, the counting starts from 0 by default. It gets the first item, and goes up to but not including the index number you specify.

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])

#get the values 10 and 20 only
print(numbers[:2])  #first to second position

#output

#array('i', [10, 20])

When you pass two numbers as arguments, you specify a range of numbers. In this case, the counting starts at the position of the first number in the range, and up to but not including the second one:

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])


#get the values 20 and 30 only
print(numbers[1:3]) #second to third position

#output

#rray('i', [20, 30])

Methods For Performing Operations on Arrays in Python

Arrays are mutable, which means they are changeable. You can change the value of the different items, add new ones, or remove any you don't want in your program anymore.

Let's see some of the most commonly used methods which are used for performing operations on arrays.

How to Change the Value of an Item in an Array

You can change the value of a specific element by speficying its position and assigning it a new value:

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])

#change the first element
#change it from having a value of 10 to having a value of 40
numbers[0] = 40

print(numbers)

#output

#array('i', [40, 20, 30])

How to Add a New Value to an Array

To add one single value at the end of an array, use the append() method:

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])

#add the integer 40 to the end of numbers
numbers.append(40)

print(numbers)

#output

#array('i', [10, 20, 30, 40])

Be aware that the new item you add needs to be the same data type as the rest of the items in the array.

Look what happens when I try to add a float to an array of integers:

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])

#add the integer 40 to the end of numbers
numbers.append(40.0)

print(numbers)

#output

#Traceback (most recent call last):
#  File "/Users/dionysialemonaki/python_articles/demo.py", line 19, in <module>
#   numbers.append(40.0)
#TypeError: 'float' object cannot be interpreted as an integer

But what if you want to add more than one value to the end an array?

Use the extend() method, which takes an iterable (such as a list of items) as an argument. Again, make sure that the new items are all the same data type.

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])

#add the integers 40,50,60 to the end of numbers
#The numbers need to be enclosed in square brackets

numbers.extend([40,50,60])

print(numbers)

#output

#array('i', [10, 20, 30, 40, 50, 60])

And what if you don't want to add an item to the end of an array? Use the insert() method, to add an item at a specific position.

The insert() function takes two arguments: the index number of the position the new element will be inserted, and the value of the new element.

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])

#add the integer 40 in the first position
#remember indexing starts at 0

numbers.insert(0,40)

print(numbers)

#output

#array('i', [40, 10, 20, 30])

How to Remove a Value from an Array

To remove an element from an array, use the remove() method and include the value as an argument to the method.

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])

numbers.remove(10)

print(numbers)

#output

#array('i', [20, 30])

With remove(), only the first instance of the value you pass as an argument will be removed.

See what happens when there are more than one identical values:

import array as arr 

#original array
numbers = arr.array('i',[10,20,30,10,20])

numbers.remove(10)

print(numbers)

#output

#array('i', [20, 30, 10, 20])

Only the first occurence of 10 is removed.

You can also use the pop() method, and specify the position of the element to be removed:

import array as arr 

#original array
numbers = arr.array('i',[10,20,30,10,20])

#remove the first instance of 10
numbers.pop(0)

print(numbers)

#output

#array('i', [20, 30, 10, 20])

Conclusion

And there you have it - you now know the basics of how to create arrays in Python using the array module. Hopefully you found this guide helpful.

Thanks for reading and happy coding!

#python #programming 

Understanding Arrays in Python

Learn how to use Python arrays. Create arrays in Python using the array module. You'll see how to define them and the different methods commonly used for performing operations on them.
 

The artcile covers arrays that you create by importing the array module. We won't cover NumPy arrays here.

Table of Contents

1. Introduction to Arrays
   1. The differences between Lists and Arrays
   2. When to use arrays
2. How to use arrays
   1. Define arrays
   2. Find the length of arrays
   3. Array indexing
   4. Search through arrays
   5. Loop through arrays
   6. Slice an array
3. Array methods for performing operations
   1. Change an existing value
   2. Add a new value
   3. Remove a value
4. Conclusion

Let's get started!

---

What are Python Arrays?

Arrays are a fundamental data structure, and an important part of most programming languages. In Python, they are containers which are able to store more than one item at the same time.

Specifically, they are an ordered collection of elements with every value being of the same data type. That is the most important thing to remember about Python arrays - the fact that they can only hold a sequence of multiple items that are of the same type.

What's the Difference between Python Lists and Python Arrays?

Lists are one of the most common data structures in Python, and a core part of the language.

Lists and arrays behave similarly.

Just like arrays, lists are an ordered sequence of elements.

They are also mutable and not fixed in size, which means they can grow and shrink throughout the life of the program. Items can be added and removed, making them very flexible to work with.

However, lists and arrays are not the same thing.

Lists store items that are of various data types. This means that a list can contain integers, floating point numbers, strings, or any other Python data type, at the same time. That is not the case with arrays.

As mentioned in the section above, arrays store only items that are of the same single data type. There are arrays that contain only integers, or only floating point numbers, or only any other Python data type you want to use.

When to Use Python Arrays

Lists are built into the Python programming language, whereas arrays aren't. Arrays are not a built-in data structure, and therefore need to be imported via the array module in order to be used.

Arrays of the array module are a thin wrapper over C arrays, and are useful when you want to work with homogeneous data.

They are also more compact and take up less memory and space which makes them more size efficient compared to lists.

If you want to perform mathematical calculations, then you should use NumPy arrays by importing the NumPy package. Besides that, you should just use Python arrays when you really need to, as lists work in a similar way and are more flexible to work with.

How to Use Arrays in Python

In order to create Python arrays, you'll first have to import the array module which contains all the necassary functions.

There are three ways you can import the array module:

1. By using import array at the top of the file. This includes the module array. You would then go on to create an array using array.array().

import array

#how you would create an array
array.array()

1. Instead of having to type array.array() all the time, you could use import array as arr at the top of the file, instead of import array alone. You would then create an array by typing arr.array(). The arr acts as an alias name, with the array constructor then immediately following it.

import array as arr

#how you would create an array
arr.array()

1. Lastly, you could also use from array import *, with * importing all the functionalities available. You would then create an array by writing the array() constructor alone.

from array import *

#how you would create an array
array()

How to Define Arrays in Python

Once you've imported the array module, you can then go on to define a Python array.

The general syntax for creating an array looks like this:

variable_name = array(typecode,[elements])

Let's break it down:

• variable_name would be the name of the array.
• The typecode specifies what kind of elements would be stored in the array. Whether it would be an array of integers, an array of floats or an array of any other Python data type. Remember that all elements should be of the same data type.
• Inside square brackets you mention the elements that would be stored in the array, with each element being separated by a comma. You can also create an empty array by just writing variable_name = array(typecode) alone, without any elements.

Below is a typecode table, with the different typecodes that can be used with the different data types when defining Python arrays:

TYPECODE	C TYPE	PYTHON TYPE	SIZE
'b'	signed char	int	1
'B'	unsigned char	int	1
'u'	wchar_t	Unicode character	2
'h'	signed short	int	2
'H'	unsigned short	int	2
'i'	signed int	int	2
'I'	unsigned int	int	2
'l'	signed long	int	4
'L'	unsigned long	int	4
'q'	signed long long	int	8
'Q'	unsigned long long	int	8
'f'	float	float	4
'd'	double	float	8

Tying everything together, here is an example of how you would define an array in Python:

import array as arr 

numbers = arr.array('i',[10,20,30])


print(numbers)

#output

#array('i', [10, 20, 30])

Let's break it down:

• First we included the array module, in this case with import array as arr .
• Then, we created a numbers array.
• We used arr.array() because of import array as arr .
• Inside the array() constructor, we first included i, for signed integer. Signed integer means that the array can include positive and negative values. Unsigned integer, with H for example, would mean that no negative values are allowed.
• Lastly, we included the values to be stored in the array in square brackets.

Keep in mind that if you tried to include values that were not of i typecode, meaning they were not integer values, you would get an error:

import array as arr 

numbers = arr.array('i',[10.0,20,30])


print(numbers)

#output

#Traceback (most recent call last):
# File "/Users/dionysialemonaki/python_articles/demo.py", line 14, in <module>
#   numbers = arr.array('i',[10.0,20,30])
#TypeError: 'float' object cannot be interpreted as an integer

In the example above, I tried to include a floating point number in the array. I got an error because this is meant to be an integer array only.

Another way to create an array is the following:

from array import *

#an array of floating point values
numbers = array('d',[10.0,20.0,30.0])

print(numbers)

#output

#array('d', [10.0, 20.0, 30.0])

The example above imported the array module via from array import * and created an array numbers of float data type. This means that it holds only floating point numbers, which is specified with the 'd' typecode.

How to Find the Length of an Array in Python

To find out the exact number of elements contained in an array, use the built-in len() method.

It will return the integer number that is equal to the total number of elements in the array you specify.

import array as arr 

numbers = arr.array('i',[10,20,30])


print(len(numbers))

#output
# 3

In the example above, the array contained three elements – 10, 20, 30 – so the length of numbers is 3.

Array Indexing and How to Access Individual Items in an Array in Python

Each item in an array has a specific address. Individual items are accessed by referencing their index number.

Indexing in Python, and in all programming languages and computing in general, starts at 0. It is important to remember that counting starts at 0 and not at 1.

To access an element, you first write the name of the array followed by square brackets. Inside the square brackets you include the item's index number.

The general syntax would look something like this:

array_name[index_value_of_item]

Here is how you would access each individual element in an array:

import array as arr 

numbers = arr.array('i',[10,20,30])

print(numbers[0]) # gets the 1st element
print(numbers[1]) # gets the 2nd element
print(numbers[2]) # gets the 3rd element

#output

#10
#20
#30

Remember that the index value of the last element of an array is always one less than the length of the array. Where n is the length of the array, n - 1 will be the index value of the last item.

Note that you can also access each individual element using negative indexing.

With negative indexing, the last element would have an index of -1, the second to last element would have an index of -2, and so on.

Here is how you would get each item in an array using that method:

import array as arr 

numbers = arr.array('i',[10,20,30])

print(numbers[-1]) #gets last item
print(numbers[-2]) #gets second to last item
print(numbers[-3]) #gets first item
 
#output

#30
#20
#10

How to Search Through an Array in Python

You can find out an element's index number by using the index() method.

You pass the value of the element being searched as the argument to the method, and the element's index number is returned.

import array as arr 

numbers = arr.array('i',[10,20,30])

#search for the index of the value 10
print(numbers.index(10))

#output

#0

If there is more than one element with the same value, the index of the first instance of the value will be returned:

import array as arr 


numbers = arr.array('i',[10,20,30,10,20,30])

#search for the index of the value 10
#will return the index number of the first instance of the value 10
print(numbers.index(10))

#output

#0

How to Loop through an Array in Python

You've seen how to access each individual element in an array and print it out on its own.

You've also seen how to print the array, using the print() method. That method gives the following result:

import array as arr 

numbers = arr.array('i',[10,20,30])

print(numbers)

#output

#array('i', [10, 20, 30])

What if you want to print each value one by one?

This is where a loop comes in handy. You can loop through the array and print out each value, one-by-one, with each loop iteration.

For this you can use a simple for loop:

import array as arr 

numbers = arr.array('i',[10,20,30])

for number in numbers:
    print(number)
    
#output
#10
#20
#30

You could also use the range() function, and pass the len() method as its parameter. This would give the same result as above:

import array as arr  

values = arr.array('i',[10,20,30])

#prints each individual value in the array
for value in range(len(values)):
    print(values[value])

#output

#10
#20
#30

How to Slice an Array in Python

To access a specific range of values inside the array, use the slicing operator, which is a colon :.

When using the slicing operator and you only include one value, the counting starts from 0 by default. It gets the first item, and goes up to but not including the index number you specify.

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])

#get the values 10 and 20 only
print(numbers[:2])  #first to second position

#output

#array('i', [10, 20])

When you pass two numbers as arguments, you specify a range of numbers. In this case, the counting starts at the position of the first number in the range, and up to but not including the second one:

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])


#get the values 20 and 30 only
print(numbers[1:3]) #second to third position

#output

#rray('i', [20, 30])

Methods For Performing Operations on Arrays in Python

Arrays are mutable, which means they are changeable. You can change the value of the different items, add new ones, or remove any you don't want in your program anymore.

Let's see some of the most commonly used methods which are used for performing operations on arrays.

How to Change the Value of an Item in an Array

You can change the value of a specific element by speficying its position and assigning it a new value:

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])

#change the first element
#change it from having a value of 10 to having a value of 40
numbers[0] = 40

print(numbers)

#output

#array('i', [40, 20, 30])

How to Add a New Value to an Array

To add one single value at the end of an array, use the append() method:

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])

#add the integer 40 to the end of numbers
numbers.append(40)

print(numbers)

#output

#array('i', [10, 20, 30, 40])

Be aware that the new item you add needs to be the same data type as the rest of the items in the array.

Look what happens when I try to add a float to an array of integers:

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])

#add the integer 40 to the end of numbers
numbers.append(40.0)

print(numbers)

#output

#Traceback (most recent call last):
#  File "/Users/dionysialemonaki/python_articles/demo.py", line 19, in <module>
#   numbers.append(40.0)
#TypeError: 'float' object cannot be interpreted as an integer

But what if you want to add more than one value to the end an array?

Use the extend() method, which takes an iterable (such as a list of items) as an argument. Again, make sure that the new items are all the same data type.

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])

#add the integers 40,50,60 to the end of numbers
#The numbers need to be enclosed in square brackets

numbers.extend([40,50,60])

print(numbers)

#output

#array('i', [10, 20, 30, 40, 50, 60])

And what if you don't want to add an item to the end of an array? Use the insert() method, to add an item at a specific position.

The insert() function takes two arguments: the index number of the position the new element will be inserted, and the value of the new element.

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])

#add the integer 40 in the first position
#remember indexing starts at 0

numbers.insert(0,40)

print(numbers)

#output

#array('i', [40, 10, 20, 30])

How to Remove a Value from an Array

To remove an element from an array, use the remove() method and include the value as an argument to the method.

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])

numbers.remove(10)

print(numbers)

#output

#array('i', [20, 30])

With remove(), only the first instance of the value you pass as an argument will be removed.

See what happens when there are more than one identical values:

import array as arr 

#original array
numbers = arr.array('i',[10,20,30,10,20])

numbers.remove(10)

print(numbers)

#output

#array('i', [20, 30, 10, 20])

Only the first occurence of 10 is removed.

You can also use the pop() method, and specify the position of the element to be removed:

import array as arr 

#original array
numbers = arr.array('i',[10,20,30,10,20])

#remove the first instance of 10
numbers.pop(0)

print(numbers)

#output

#array('i', [20, 30, 10, 20])

Conclusion

And there you have it - you now know the basics of how to create arrays in Python using the array module. Hopefully you found this guide helpful.

You'll start from the basics and learn in an interacitve and beginner-friendly way. You'll also build five projects at the end to put into practice and help reinforce what you learned.

Thanks for reading and happy coding!

Original article source at https://www.freecodecamp.org

#python 

How to Install OpenJDK 11 on CentOS 8

What is OpenJDK?

OpenJDk or Open Java Development Kit is a free, open-source framework of the Java Platform, Standard Edition (or Java SE). It contains the virtual machine, the Java Class Library, and the Java compiler. The difference between the Oracle OpenJDK and Oracle JDK is that OpenJDK is a source code reference point for the open-source model. Simultaneously, the Oracle JDK is a continuation or advanced model of the OpenJDK, which is not open source and requires a license to use.

In this article, we will be installing OpenJDK on Centos 8.

#tutorials #alternatives #centos #centos 8 #configuration #dnf #frameworks #java #java development kit #java ee #java environment variables #java framework #java jdk #java jre #java platform #java sdk #java se #jdk #jre #open java development kit #open source #openjdk #openjdk 11 #openjdk 8 #openjdk runtime environment

How to Print an Array in Java

Introduction

Printing an array is a quick way to give us visibility on the values of the contents inside. Sometimes the array values are the desired output of the program.

In this article, we’ll take a look at how to print an array in Java using four different ways.

While the “best way” depends on what your program needs to do, we begin with the simplest method for printing and then show more verbose ways to do it.

• Print an Array Using Arrays.toString() and Arrays.deepToString()
• Print an Array Using Java 8 Streams
• Print an Array by Converting to List
• Print an Array Using For Loops
• Converting To List and Using an Iterator

#java #array #how to print an array in java #array in java #print an array in java #print

Going Beyond Java 8: Local Variable Type Inference (var) - DZone Java

According to some surveys, such as JetBrains’s great survey, Java 8 is currently the most used version of Java, despite being a 2014 release.

What you are reading is one in a series of articles titled ‘Going beyond Java 8,’ inspired by the contents of my book, Java for Aliens. These articles will guide you step-by-step through the most important features introduced to the language, starting from version 9. The aim is to make you aware of how important it is to move forward from Java 8, explaining the enormous advantages that the latest versions of the language offer.

In this article, we will talk about the most important new feature introduced with Java 10. Officially called local variable type inference, this feature is better known as the **introduction of the word **var. Despite the complicated name, it is actually quite a simple feature to use. However, some observations need to be made before we can see the impact that the introduction of the word var has on other pre-existing characteristics.

#java #java 11 #java 10 #java 12 #var #java 14 #java 13 #java 15 #verbosity