Types using arrays java

Arrays in Java

Array in java is a group of like-typed variables referred to by a common name. Arrays in Java work differently than they do in C/C++. Following are some important points about Java arrays.

• In Java, all arrays are dynamically allocated. (discussed below)
• Arrays are stored in contiguous memory [consecutive memory locations].
• Since arrays are objects in Java, we can find their length using the object property length. This is different from C/C++, where we find length using sizeof.
• A Java array variable can also be declared like other variables with [] after the data type.
• The variables in the array are ordered, and each has an index beginning with 0.
• Java array can also be used as a static field, a local variable, or a method parameter.
• The size of an array must be specified by int or short value and not long.
• The direct superclass of an array type is Object.
• Every array type implements the interfaces Cloneable and java.io.Serializable.
• This storage of arrays helps us randomly access the elements of an array [Support Random Access].
• The size of the array cannot be altered(once initialized). However, an array reference can be made to point to another array.

An array can contain primitives (int, char, etc.) and object (or non-primitive) references of a class depending on the definition of the array. In the case of primitive data types, the actual values are stored in contiguous memory locations. In the case of class objects, the actual objects are stored in a heap segment.

Creating, initializing, and accessing an Array

One-Dimensional Arrays:

The general form of a one-dimensional array declaration is

type var-name[]; OR type[] var-name;

An array declaration has two components: the type and the name. type declares the element type of the array. The element type determines the data type of each element that comprises the array. Like an array of integers, we can also create an array of other primitive data types like char, float, double, etc., or user-defined data types (objects of a class). Thus, the element type for the array determines what type of data the array will hold.

// both are valid declarations int intArray[]; or int[] intArray; byte byteArray[]; short shortsArray[]; boolean booleanArray[]; long longArray[]; float floatArray[]; double doubleArray[]; char charArray[]; // an array of references to objects of // the class MyClass (a class created by // user) MyClass myClassArray[]; Object[] ao, // array of Object Collection[] ca; // array of Collection // of unknown type

Although the first declaration establishes that int Array is an array variable, no actual array exists. It merely tells the compiler that this variable (int Array) will hold an array of the integer type. To link int Array with an actual, physical array of integers, you must allocate one using new and assign it to int Array.

Instantiating an Array in Java

When an array is declared, only a reference of an array is created. To create or give memory to the array, you create an array like this: The general form of new as it applies to one-dimensional arrays appears as follows:

Here, type specifies the type of data being allocated, size determines the number of elements in the array, and var-name is the name of the array variable that is linked to the array. To use new to allocate an array, you must specify the type and number of elements to allocate.

int intArray[]; //declaring array intArray = new int[20]; // allocating memory to array

int[] intArray = new int[20]; // combining both statements in one

Note:

The elements in the array allocated by new will automatically be initialized to zero (for numeric types), false (for boolean), or null (for reference types). Do refer to default array values in Java.

Obtaining an array is a two-step process. First, you must declare a variable of the desired array type. Second, you must allocate the memory to hold the array, using new, and assign it to the array variable. Thus, in Java, all arrays are dynamically allocated.

Array Literal

In a situation where the size of the array and variables of the array are already known, array literals can be used.

int[] intArray = new int[]< 1,2,3,4,5,6,7,8,9,10 >; // Declaring array literal

• The length of this array determines the length of the created array.
• There is no need to write the new int[] part in the latest versions of Java.

Accessing Java Array Elements using for Loop

Each element in the array is accessed via its index. The index begins with 0 and ends at (total array size)-1. All the elements of array can be accessed using Java for Loop.

// accessing the elements of the specified array for (int i = 0; i < arr.length; i++) System.out.println("Element at index " + i + " : "+ arr[i]);

Implementation:

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