Java static array in class

Инициализация массива статических объектов в Java

В C++ общеизвестной и полезной практикой является использование списка инициализации для задания значений массива. При этом крайне удобно инициализировать при помощи фигурных скобок объекты в которых поля являются открытыми. Это либо структуры(struct) либо классы, у которых все поля открыты(перед ними указан access specifier как public).

Рассмотрим обычную структуру :

struct my_unary_function  string name; string detect_name; double (*handler) (double); >;

Объекты можно создавать и инициализировать на лету(конструктор нам не нужен!) :

my_unary_function sin_func = "Синус", "sin", sin>;

Обратите внимание на синтаксис — во-первых, наличие фигурных скобок. Во-вторых — строгий порядок перечисления значений , соответствующий порядку определения переменных в структуре. У нового объекта — name=”Синус”, detec_name=”sin”, handler=”&sin”.

Теперь, собственно массивы, которые удобно инициализировать также как объекты :

my_unary_function math_functions[] =  "Синус", "sin", sin>, "Косинус", "cos", cos>, "Тангенс", "tan", tan> >;

Добавив всего-лишь одну строчку расширится функционал программы. Если пишется калькулятор с поддержкой простейших математических вычислений — то все функции можно определять по полю detect_name в этом массиве, а обработчик определяется полем handler.

Java — встроенная инициализация статических массивов из объектов. В Java — немного другая история. Чаще всего используются статические массивы, тип элементов которых объявлен рядом с ними.

Пример такого определения :

public class InnerClassTest  static class Employee  private String name; private double salary; public Employee(String n, double s)  name = n; salary = s; > public void print()  System.out.println(name + " " + salary); > > static Employee[] staff = new Employee[]  new Employee("Harry Hacker", 3500), new Employee("Carl Cracker", 7500), new Employee("Tony Tester", 3800), >; public static void main(String[] args)  for (Employee e: staff)  e.print(); > > >

А можно было бы разделить инициализацию и поместить её в специальный static-блок :

public class Main  static Integer[] integerArray; static  integerArray = new Integer[]  new Integer(1), new Integer(2) >; > public static void main(String args[])  for (int i = 0; i  integerArray.length; i++)  System.out.println(integerArray[i]); > > >

Такой static-блок является функциональным блоком и в нём также можно выполнять любые действия :

 static ArrayListString> list = new ArrayListString>(); static  list.add("Bart"); list.add("Lisa"); list.add("Marge"); list.add("Barney"); list.add("Homer"); list.add("Maggie"); System.out.print("Hello!"); >

На самом деле для инициализации ArrayList можно использовать метод java.util.Arrays.asList :

public static final ListString> favorites = Arrays.asList("EJB", "JPA", "Glassfish", "NetBeans");

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Java static array in class

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How to declare a static String array in Java

Following program shows how to declare a static string array.

Example

public class Tester < private static String[] array; static < array = new String[2]; array[0] = "Hello"; array[1] = "World"; >public static void main(String[] args) < System.out.println("Array: "); for(int i = 0; i < array.length; i++)< System.out.print(array[i] + " "); >> >

Output

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Static Array in Java

In Java, array is the most important data structure that contains elements of the same type. It stores elements in contiguous memory allocation. There are two types of array i.e. static array and dynamic array. In this section, we will focus only on static array in Java.

Static Array

An array that is declared with the static keyword is known as static array. It allocates memory at compile-time whose size is fixed. We cannot alter the static array.

If we want an array to be sized based on input from the user, then we cannot use static arrays. In such a case, dynamic arrays allow us to specify the size of an array at run-time.

Static Array Example

For example, int arr[10] creates an array of size 10. It means we can insert only 10 elements; we cannot add a 11th element as the size of Array is fixed.

Advantages of Static Array

• It has efficient execution time.
• The lifetime of static allocation is the entire run time of the program.

Disadvantages of Static Array

• In case more static data space is declared than needed, there is waste of space.
• In case less static space is declared than needed, then it becomes impossible to expand this fixed size during run time.

Declaring a Static Array

The syntax to declare a static array is:

We can also declare and initialize static array as follows:

Static array can also be declared as a List. For example:

Static Array Java Program

StaticArrayExample.java

Let’s see another Java program.

StaticArrayExample.java

Difference Between Static Array and Dynamic Array

The following table describes the key differences between static array and dynamic array.

Static Array	Dynamic Array
Static arrays are allocated memory at compile time.	Dynamic array is located at run-time.
The size of static array is fixed.	The size of dynamic array is fixed.
It is located in stack memory space.	It is located in heap memory space.
int array[10]; //array of size 10	int* array = new int[10];

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